04.01 - Clinical Neuroendoscopy.pdf

CLINICAL NEUROENDOSCOPY

CONTENTS

Preface Rick Abbott

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History of Neuroendoscopy Rick Abbott

1

Since the beginnings of medicine, physicians have sought minimally invasive ways to peer into body body cavities. cavities. It is only in the last several several decades decades that the promises promises of endoscopy have begun to be answered. answered. What follows follows is a brief brief outline of the development development of  endoscopic technology and its application to the nervous system both for diagnostic and therapeutic procedures.

The Endoscopic Management of Arachnoidal Cysts Rick Abbott

9

There is little doubt that most arachnoidal cysts will be managed endoscopically in the future given the advances we have seen over the last decade in our instrumentation. Excitement to employ this new technology should be governed by the reality that we are still learning and that our current success rate is not quite as good as what can be expected when using microneurosurgery.

Basic Principles and Equipment in Neuroendoscopy Vit Siomin and Shlomi Constantini

19

Understanding some of the basic principles of endoscopy and awareness of available resources can potentially be of considerable help to experienced neurosurgeons as well as  beginners in selection of the most appropriate tools for different procedures and making cost-effective choices when browsing through multiple commercial advertisements and purchasing new equipment. Although numerous advantages in science and industry have made it possible to offer a wide variety of neuroendoscopes and tools, we believe the major achievements in this field are yet to occur. This particularly refers to the development of smaller fiberoptic scopes with better image quality and three-dimensional endoscopes and to the invention of more efficient tools for endoscopic tumor removal with the same degree of safety as in open surgery.

The Anatomy of the Ventricular System David G. McLone

33

The embryology of the ventricular development of the brain assists in understanding the final relations between structures forming these cavities. An accurate concept of this anatomy allows the endoscopist to maneuver within the ventricular system. VOLUME 15  NUMBER 1  JANUARY 2004

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Selecting Patients for Endoscopic Third Ventriculostomy Harold L. Rekate

39

Endoscopic third ventriculostomy has been used for about 70 years in the treatment of  hydrocephalus but was generally abandoned with the development of valve-regulated shunts. shunts. With improvem improvements ents in the understand understanding ing of the pathophys pathophysiolo iology gy of hydrohydrocephalus and technical equipment improvements for endoscopy, there has been a resurgence of interest in the procedure. Late-onset aqueductal stenosis is the ideal pathologic condition responding to this treatment, but there are multiple other conditions that are potentially responsive to internal bypass. All patients in whom the ventricles expand at the time of shunt failure should be considered as candidates.

Techniques of Endoscopic Third Ventriculostomy Douglas Brockmeyer

51

Modern techniques of endoscopic third ventriculostomy (ETV) are based on the concept of establishing a natural conduit for cerebral spinal fluid (CSF) flow through the floor of  the third ventricle. Through the years, a wide variety of techniques have been used as a means to this end and have included both open and closed approaches. However, the relatively recent application of endoscopic technology to intraventricular surgery has allowed allowed neurosurg neurosurgeons eons to perform perform third ventriculost ventriculostomie omiess in a minimally minimally invasive fashion. Advances in third ventriculostomy technique have been based on a detailed understanding of third ventricular anatomy, surgical trajectories, and improved instrumentation. The goal of this article is to discuss these issues in detail and to point out the relevant risks and known complications associated with them.

Complications of Third Ventriculostomy Marion L. Walker

61

As experience with ETV grows, the procedure will be performed by an increasing num ber of neurosurgeons. neurosurgeons. Although the technique has been greatly refined since its advent almost a century ago, today’s neurosurgeon must never forget that this seemingly simple procedure holds the potential for a number of devastating complications. Appropriate training training and experience experience are important important to the success success of ETV and for avoiding complicacomplications. It is imperative that surgeons continue to report their experience with the complications of ETV so that the procedure can continue to be made as safe as possible.

Results of Endoscopic Third Ventriculostomy Mark R. Iantosca, Walter J. Hader, and James M. Drake

67

Endoscopic third ventriculostomy is emerging as the treatment of choice for aqueductal stenosis caused by anatomic, inflammatory, and selected neoplastic etiologies. The technique has also proven useful in the pathologic diagnosis and treatment of these conditions. tions. Long-t Long-term erm result resultss of this this proced procedur uree and compar compariso ison n to standa standard rd shunti shunting ng procedures are necessary to define indications for patients with pathologic findings in the intermediate response groups. Development of new studies for preoperative assessment of cerebrospinal fluid absorptive capacity and quantitative postoperative measures of ventriculostomy function would be invaluable additions to our ability to assess candidates for this procedure and their eventual outcome. Further study and technical refinements will, no doubt, lead to many more potential uses for these procedures in the treatment of hydrocephalus and its associated etiologies. The challenge for neurosurgeons will be to define the operative indications and outcomes, while refining techniques for safely performing these useful procedures.

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CONTENTS

Selecting Patients for Endoscopic Third Ventriculostomy Harold L. Rekate

39

Endoscopic third ventriculostomy has been used for about 70 years in the treatment of  hydrocephalus but was generally abandoned with the development of valve-regulated shunts. shunts. With improvem improvements ents in the understand understanding ing of the pathophys pathophysiolo iology gy of hydrohydrocephalus and technical equipment improvements for endoscopy, there has been a resurgence of interest in the procedure. Late-onset aqueductal stenosis is the ideal pathologic condition responding to this treatment, but there are multiple other conditions that are potentially responsive to internal bypass. All patients in whom the ventricles expand at the time of shunt failure should be considered as candidates.

Techniques of Endoscopic Third Ventriculostomy Douglas Brockmeyer

51

Modern techniques of endoscopic third ventriculostomy (ETV) are based on the concept of establishing a natural conduit for cerebral spinal fluid (CSF) flow through the floor of  the third ventricle. Through the years, a wide variety of techniques have been used as a means to this end and have included both open and closed approaches. However, the relatively recent application of endoscopic technology to intraventricular surgery has allowed allowed neurosurg neurosurgeons eons to perform perform third ventriculost ventriculostomie omiess in a minimally minimally invasive fashion. Advances in third ventriculostomy technique have been based on a detailed understanding of third ventricular anatomy, surgical trajectories, and improved instrumentation. The goal of this article is to discuss these issues in detail and to point out the relevant risks and known complications associated with them.

Complications of Third Ventriculostomy Marion L. Walker

61

As experience with ETV grows, the procedure will be performed by an increasing num ber of neurosurgeons. neurosurgeons. Although the technique has been greatly refined since its advent almost a century ago, today’s neurosurgeon must never forget that this seemingly simple procedure holds the potential for a number of devastating complications. Appropriate training training and experience experience are important important to the success success of ETV and for avoiding complicacomplications. It is imperative that surgeons continue to report their experience with the complications of ETV so that the procedure can continue to be made as safe as possible.

Results of Endoscopic Third Ventriculostomy Mark R. Iantosca, Walter J. Hader, and James M. Drake

67

Endoscopic third ventriculostomy is emerging as the treatment of choice for aqueductal stenosis caused by anatomic, inflammatory, and selected neoplastic etiologies. The technique has also proven useful in the pathologic diagnosis and treatment of these conditions. tions. Long-t Long-term erm result resultss of this this proced procedur uree and compar compariso ison n to standa standard rd shunti shunting ng procedures are necessary to define indications for patients with pathologic findings in the intermediate response groups. Development of new studies for preoperative assessment of cerebrospinal fluid absorptive capacity and quantitative postoperative measures of ventriculostomy function would be invaluable additions to our ability to assess candidates for this procedure and their eventual outcome. Further study and technical refinements will, no doubt, lead to many more potential uses for these procedures in the treatment of hydrocephalus and its associated etiologies. The challenge for neurosurgeons will be to define the operative indications and outcomes, while refining techniques for safely performing these useful procedures.

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CONTENTS

Loculated Ventricles and Isolated Compartments in Hydrocephalus: Their  Pathophysiology and the Efficacy of Neuroendoscopic Surgery Shizuo Oi and Rick Abbott

77

Trapped cerebrospinal fluid spaces can, on occasion, complicate the management of  hydrocephalus and present the surgeon with a treatment dilemma. This condition can  be categorized into one of two types: those arising as a complication of shunting and those that arise as a complication of an inflammatory process within the ventricles. Whatever the cause, the result is a significant escalation in the complexity of the management of the patient. Neuroendoscopy is typically viewed as an attractive treatment alternative in such a setting because of its minimalistic and thus seemingly simplistic nature. We have learned that nothing could be further from the truth. This article reviews the various entities that can arise in the hydrocephalic patient, how they can be managed endoscopically, and what sort of result can be expected.

Neuro-oncologic Applications of Endoscopy Charles Teo and Peter Nakaji

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Neuro-oncology, in all its aspects, provides an ideal venue for the application of endoscopy. The main obstacle to its use has been neurosurgeons’ lack of familiarity with the techniques and their advantages. As the neuro-oncologic surgeon uses the endoscope more, endoscopy will take its rightful place in the surgeon’s armamentarium. The advantages of improved visualization of intraventricular pathology, better management of tumor-related hydrocephalus, less morbid biopsies, and minimally invasive removal of intraventricular tumors are invaluable adjuncts to traditional tumor management. Furthermore, endoscopy is the logical next step for surpassing the limitations of traditional microsurgery. Endoscopy is still in its infancy. Rigorous application of the technology is increasingly allowing us to provide our patients the most maximally effective and minimally invasive surgery possible.

Index

CONTENTS

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FORTHCOMING ISSUES April 2004 Traumatic Neurovascular Surgery  J. Paul Elliot, MD,  Guest Editor  July 2004 Pain Treatment Gary Heit, MD,  Guest Editor October 2004 Metastatic Spine Tumors Meic Schmidt, MD,  Guest Editor

RECENT ISSUES October 2003 Intraventricular Tumors Andrew T. Parsa, MD, PhD, and Mitchel S. Berger, MD,  Guest Editors  July 2003 Neuroaugmentation for  Chronic Pain  Jaimie M. Henderson, MD,  Guest Editor April 2003 Surgery for Psychiatric Disorders Ali R. Rezai, MD, Steven A. Rasmussen, MD, and Benjamin D. Greenberg, MD, PhD Guest Editors

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Neurosurg Clin N Am 15 (2004) ix

Preface

Clinical neuroendoscopy

Rick Abbott, MD Guest Editor

Neuroendoscopy has come of age over the last decade and is now an invaluable tool to the practice of neurosurgery. This is particularly the case in practices with large volumes of patients with hydrocephalus. This issue of the   Neurosurgery Clinics of North America is dedicated to neuroendoscopy with an emphasis on its use in the treatment of hydrocephalus. Readers will find helpful articles on instrumentation and anatomy as well as several articles on various aspects of use for hydrocephalus and related conditions. With a

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look toward the future there is also an article on the use of the endoscopy in the removal of brain tumors. By reading this issue, readers will gain an appreciation of the state-of-the-art of intracranial neuroendoscopy. Rick Abbott, MD Inn, Beth Israel Medical Center 170 East End Avenue New York, NY 10128, USA E-mail address: [email protected]

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Neurosurg Clin N Am 15 (2004) 1–7

History of neuroendoscopy Rick Abbott, MD Clinical Neuroendoscopy, INN, Beth Israel Medical Center, 170 East End Avenue, New York, NY 10128, USA

The insertion of tubes into the body for either the deliverance of a therapy or diagnostic purposes has taken place throughout recorded medicine. The first documented instance of the use of a tube to inspect the rectum was in Hippocrates’ time. Natural light was used to illuminate the field [1]. The Babylonians described using vaginal speculums in 500 AD,   with illumination being provided by ambient light [2].   Abulkaism (980–1037) and Giulio Cesare Aranzi (1530–1589) reported on the use of mirrors to reflect ambient light down their ‘‘endoscopic’’ tubes to allow for the inspection of deeper body cavities  [3]. In 1805, the Alert Faculty in Vienna heard Philippe Bozzini’s report on an instrument he had developed, which used candle light reflected by a concave mirror for the inspection of the bladder and rectum [4]. They were not impressed, censoring Bozzini for his inappropriate curiosity and rejecting the ‘‘magic lantern.’’ In 1867, Antonin Desormeaux published a description of an endoscope whose illumination had been improved by using an alcohol and kerosene burning candle with a chimney [5]. The light this candle generated was collected and focused down the shaft of the scope using a lens. This was to be the first successful design for a cystoscope, and it was presented to the Academy of Medicine in Paris. Shortly thereafter, there were several reports of therapeutic uses for endoscopes. First, Bevan reported on successfully using an endoscope to extract foreign material from the esophagus, and Pantaleoni then reported on using a scope to inspect the uterus of a women bothered by postmenopausal bleeding, discovering an intrauterine polyp and cauterizing it with silver

E-mail address:   [email protected]

nitrate [4]. In 1870, Kussmaul demonstrated using a rigid scope to inspect the stomach [5]. The assistance of a professional sword swallower was required for this, however. All these described systems suffered from a lack of magnification. They were simply tubes that directed illumination down to their distal tip. In 1879, Max Nitze described the first system that contained a series of lens [6]. Working with several opticians, he described a scope with an illumination source to the distal tip, a platinum wire that glowed when current was conducted through it. The light produced was then projected through a prism. This wire produced heat, however, necessitating a water coolant system. Shortly thereafter, Edison invented the light bulb, and Newman then described modifying Nitze’s scope in 1883 by substituting a small light bulb at the distal tip for the platinum wire [7].   Boisseau du Rocher was the next to modify the system by fabricating an outer sheath to contain the telescope, reporting on this in 1889 [4]. This modification allowed the surgeon to interchange different scopes during a procedure without having to renavigate through the body to the working site. By the turn of the century, the promise of  endoscopy had been demonstrated, but its acceptance was slowed because of the poor illumination. Indeed, Pantaleoni’s students remarked on not being able to appreciate his work, claiming an inability to see anything with his hysteroscope [4]. The light source evolved during the first half of  the twentieth century, and by 1950, it consisted of  a tungsten bulb at the distal tip of the scope [8]. Even this was inadequate, providing poor illumination and significant color distortion. In large part, these difficulties were the result of design flaws inherent in the Nitze endoscope design (ie,

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R. Abbott/ Neurosurg Clin N Am 15 (2004) 1–7 

a telescope containing a series of lens housed in an air-filled tube) [9]. The conduction of light in an endoscope is a function of the refractory index of  the conducting medium, in this case, air. The refractory index is defined as the difference in the speed of light conduction in a vacuum and the medium in question. As it turns out, the refractory index for glass is 1.5 times greater than that for air. Harold Hopkins, a British optical physicist, used this observation to construct a new endoscope designed to improve on light conduction. His scope interchanged glass for air and vice versa, resulting in a series of ‘‘air lens’’ housed in a glass tube, or a series of glass rods. Not only did this result in an increase in the system’s refractory index but also in an increase in the scope’s field of  view because of a decrease in spherical aberration at the perimeter of the lens (thus increasing the lens’s light gathering capacity). The net gain in light transmission of Hopkins’ scope design over Nitze’s design was ninefold. Hopkins also used coating on the lens to minimize refraction of light at the lens interface with the glass rods and calculated the layout of the lens to eliminate ghosting and chromatic distortion in addition to further increasing light transmission. With these improvements, serious attention could be given to using scopes within the human body, such as the brain’s ventricles, where ambient light could not be directed. An additional problem with the Nitze design was the heat generated by its illumination source housed at the distal tip of the scope. The answer seemed to be using a light generator outside of  the body and conducting the light down to the distal tip. The first report of use of an external light source was by Fourestier, Bladu, and Valmier in 1952, when a scope design was described where light was transmitted down a quartz rod from the scope’s external light source [8]. This transmitted enough light to make endoscopic photography possible. An improvement on this shortly followed based on work done by Heinrich Lamm in 1932 [4].   At that time, Lamm had demonstrated that light could be conducted through a bundle of glass fibers. In 1954, Harold Hopkins picked up on this idea and with a colleague, N.S. Kapany, discussed applying this finding to design a more effective light conducting system  [10]. They described two types of fiber bundles, so-called ‘‘incoherent’’ and ‘‘coherent’’ bundles. Incoherent bundles referred to bundles of glass fibers whose orientation with neighbors was chaotic or without order. This

type of bundle could be used to transmit light for illumination. Conversely, a coherent bundle maintained the orientation of fibers through its length so that any given fiber would maintain its exact orientation to it is neighbors throughout the length of the bundle. This type of bundle could be used to transmit an image from one end of the bundle to the other. Hopkins and Kapany observed that this type of bundle could be used in the design of a ‘‘flexible’’ endoscope whose shaft could be bent to a degree and still allow for the conduction of an image from one end of the scope to the other. In the same issue of  Nature, there was a paper describing a technique for coating the fibers to minimize loss of light and degradation of image quality [5]. Hirschowitz visited Hopkins’ laboratory shortly after the publication of his paper in 1954 and was impressed with the promise of the observations made by Hopkins and Kapany [5]. He returned to the University of Michigan, where he collaborated with Wilbur Peters and Lawrence Curtiss to develop a fiberoptic gastroscope. By the end of 1956, Curtiss had developed a glass coating for the optical fibers that was permanently adherent and capable of conducting an image for over a meter. In January 1957, they completed construction of their first fiberoptic gastroscope. The next month, it was used to inspect a gastric ulcer in the wife of a dental student. Within 3 years, a commercial fiberoptic endoscope, American Cystoscope Makers’ No. 4990 (American Cystoscope Makers, New York, NY), became available. By 1962, Hirschowitz was able to publish a series of 500 gastroesophageal endoscopies. In 1963, Guiot described an endoscope developed for intracranial work that had a powerful external light source whose illumination was conducted via a quartz rod to the scope’s distal tip [9]. This allowed for color photography of the ventricle. That same year Scarff described improving his ventriculoscope by substituting a ‘‘fiber lighting’’ system with an external light source for the previously used incandescent bulb at the scope’s distal tip [9].   In 1983, the Welch Allyn Company (Skaneateles Falls, NY) released the first endoscope with the charged couple device, allowing for conduction of a high-quality image from the scope to a television screen [5]. Other companies quickly followed with miniaturization of the scopes, resulting in an improved ability to document and teach. The ability to introduce rigid and flexible endoscopes into the body and to obtain good-quality images was thus established.

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As the use of endoscopes for diagnostic purposes increased, not surprisingly, so too did the desire to render therapy. In 1887, Felix M. Oberla ¨nder described the first scope designed to treat postgonorrheal strictures [6].   The scope allowed for direct visualization of the urethra and contained an instrument channel allowing for the introduction of various knives for cutting the strictures under direct vision. In 1910, L’Espinasse reported to a local medical society in Chicago on the use a cystoscope to fulgurate the choroid plexus in two infants with hydrocephalus   [11]. One child died immediately after surgery, but the other lived for 5 years; thus was reported the first therapeutic neuroendoscopic case. Erich Wossidlo, a German urologist, reported on using a galvanocaustic hook to treat urethral strictures [6]. In 1937, Ruddock introduced a scope that contained an electrocautery unit and biopsy forceps as well as ancillary biopsy instruments for use in the peritoneal cavity   [12]. In 1939, Crafoord and Frenckner described using sclerotherapy to treat esophageal varices [4]. In the 1970s, lasers were introduced into the armamentarium of medicine. In 1973, Nath and his colleagues  [13]   experimentally used an Nd:YAG laser fiber with an endoscope to demonstrate its feasibility. Two years later, Fru  ¨ hmorgan et al [14] reported on its use on a patient. Although not as aggressive as some specialists, neurosurgeons have been actively engaged in the development of endoscopic applications for the central nervous system. As mentioned earlier, L’Espinasse first described use of the endoscope in the central nervous system in 1910. In 1922, Dandy   [15]   reported performing an endoscopic choroid plexectomy after a previously reported experience in performing open choroid plexectomy on four patients. The attempt to perform the endoscopic choroid plexectomy was unsuccessful, and he did not attempt any further such cases. The next year, Fay and Grant   [16]   reported on successfully photographing the interior of the ventricles of a hydrocephalic child. The fact that a 40-second exposure was required speaks to the rather poor illumination available at that time. In the same year, Mixter   [17]   performed the first successful endoscopic third ventriculostomy using a cystoscope. This did not gain acceptance, presumably because of the poor visualization. In 1932, Dandy [18] reported on using a cystoscope to remove the choroid plexus. His results were similar to those experienced when he did the surgery via a formal craniotomy. Shortly there-

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after, Putnam [19] reported on the effectiveness of  simply cauterizing the choroid plexus using a scope of his design. Scarff   [20]   then wrote a paper on his experience in developing a ventriculoscope that allowed cauterization of the choroid plexus. He went on to develop a scope that contained a movable electrode for cauterization of the plexus. In 1943, Putnam [21] reported on performing endoscopic choroid plexectomy on 42 patients. There were 10 (25%) perioperative deaths. Fifteen of the patients failed to respond to the treatment, but 17 experienced success in relief  of their intracranial hypertension. In 1970, Scarff  [22]   reviewed all available series of endoscopic choroid plexus cauterization for the treatment of hydrocephalus. Of 95 patients so treated, 14 (15%) had died, whereas 52 (60%) had initial successful results. Scarff also looked at his patients (39 of the 95 patients) at more than 5 years after their surgery and found that 7 had died of causes unrelated to their hydrocephalus and the rest required no further treatment. More recently, Bucholz and Pittman   [23]   reported on using the Nd:YAG laser to cauterize the choroid plexus of  a shunted infant with ascites, effectively decreasing cerebrospinal fluid (CSF) production by 50%. Pople and Griffith  [24] commented on their 20-year experience treating 156 individuals with choroid plexus cauterization, finding a 35% longterm success rate. As stated earlier, Guiot reported on an endoscope with a powerful external light source sufficient to allow for color photography of the ventricle. Guiot reported on using this system to perform third ventriculostomy. The difficulty with his system was its diameter, 9.1 mm. This prevented a wider use of his scope, and Guiot ultimately ceased performing third ventriculostomy with his instrument. Vries  [25] described his experience with five hydrocephalic patients on whom he performed endoscopic third ventriculostomies in 1978. Although he showed that the procedure was technically feasible, none of his patients remained without a shunt over the long term. Jones et al   [26] reported a different experience in 1990, describing a 50% success rate in long-term management of hydrocephalus in 24 patients who underwent a third ventriculostomy. Modern series have improved on this figure, with most now reporting 60% to 90% long-term success with the technique  [27–33]. Neurosurgeons have used endoscopes for other indications in the central nervous system. In 1938, Pool [34] reported on using an endoscope, termed

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a myeloscope, to visualize dorsal nerve roots of the cauda equina. Several years later, he described using the instrument to view the spinal cord and its conus. In 1990, the group at Hoˆpital Necker in Paris described their evolution in the treatment of suprasellar arachnoidal cysts  [35].   From first performing stereotactically guided fenestration of  the cyst, they moved to performing the procedure endoscopically. Others have reported on endoscopically fenestrating other arachnoidal cysts [36–41]. Although technically more challenging, the endoscope can be used to fenestrate other intraventricular cysts such as arise after severe ventriculitis. In 1986, Powers   [42]   described two infants with postinfectious multicystic ventricles who he managed using a flexible endoscope and argon laser. He was able to fenestrate the cysts into the ventricles successfully and cure the lingering infections. In 1992, Zamorano et al described using a stereotactically guided endoscope to treat cystic ventricles and other entities [64]. The endoscope has also been used to assist in the evacuation of intracranial hematomas  [43–45]. The greatest success has been with chronic hematomas, but surgeons have described attacking even acute clots [11,46,47]. There are now numerous reports in the literature of the successful biopsying or removal of intracranial mass lesions endoscopically. In 1983, Powell et al   [48]   first reported on the removal of a colloid cyst using the endoscope. There have been many reports since [40,49–51,53], and in 1994, Lewis et al [52] showed that this type of resection required less surgical time and postoperative convalescence for their patients. Fukushima   [54]   reported on using a flexible endoscope to biopsy tumors in 1978. Many have reported similar success over the past several decades [55–60]. Endoscopic surgery has also been used to manage cystic tumors, such as craniopharyngiomas, fenestrating the cysts into ventricles or cisternal spaces   [61–65]. One particular successful application for the neuroendoscope has been to biopsy pineal region tumors when performing third ventriculostomies to treat the associated hydrocephalus  [66,67]. There has been one report, however, of secondary seeding of the endoscope’s tract after such a biopsy  [68]. As early as 1979, surgeons reported on using the endoscope to resect pituitary lesions, and this has become extremely popular over the last decade  [65,69–81]. Finally, there are several surgeons investigating the utility of using an endoscope as an assisting set of eyes when performing microneurosurgery

[60,61]. This has allowed for a much narrower surgical corridor and for the surgeon to ‘‘look around corners’’ or on the back side of structures, such as arteries. Fries and Perneczky   [11]   have also spoken of improved appreciation of microanatomy not apparent with the microscope. Other applications are finding their way into the literature as neurosurgeons gain comfort in using endoscopic equipment. Jimenez and Barone [82,83]  have reported on using the endoscope to perform sagittal strip craniectomies in conjunction with molding helmets for the treatment of  scaphocephaly. As early as 1993, neurosurgeons reported on using endoscopes to perform thoracic sympathectomies in a minimally invasive fashion [84–89]. In 1994, Schaffer   [90]   reported on resection of an intervertebral disk using an endoscope, and several surgeons have described using the endoscope to perform various spinal surgeries since [91–95]. It seems clear that the endoscope is a unique tool and that it has a place in the armamentarium of the modern neurosurgeon. Its applications will only broaden as we gain instrumentation and experience in using this system.

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[43] Auer LM. Ultrasound stereotaxic endoscopy in neurosurgery. Acta Neurochir Suppl (Wien) 1992; 54:34–41. [44] Bauer BL, Hellwig D. Minimally invasive endoscopic neurosurgery—a survey. Acta Neurochir Suppl (Wien) 1994;61:1–12. [45] Karakhan VB, Khodnevich AA. Endoscopic surgery of traumatic intracranial haemorrhages. Acta Neurochir Suppl (Wien) 1994;61:84–91. [46] Auer LM, Holzer P, Ascher PW, Heppner F. Endoscopic neurosurgery. Acta Neurochir (Wien) 1988; 90(1–2):1–14. [47] Hellwig D, Bauer BL. Minimally invasive neurosurgery by means of ultrathin endoscopes. Acta Neurochir Suppl (Wien) 1992;54:63–8. [48] Powell MP, Torrens MJ, Thomson JL, Horgan JG. Isodense colloid cysts of the third ventricle: a diagnostic and therapeutic problem resolved by ventriculoscopy. Neurosurgery 1983;13(3):234–7. [49] Rodziewicz GS, Smith MV, Hodge CJ Jr. Endoscopic colloid cyst surgery. Neurosurgery 2000;46(3): 655–62. [50] King WA, Ullman JS, Frazee JG, Post KD, Bergsneider M. Endoscopic resection of colloid cysts: surgical considerations using the rigid endoscope. Neurosurgery 1999;44(5):1103–11. [51] Deinsberger W, Boker DK, Samii M. Flexible endoscopes in treatment of colloid cysts of the third ventricle. Minim Invasive Neurosurg 1994; 37(1):12–6. [52] Lewis AI, Crone KR, Taha J, van Loveren HR, Yeh HS, Tew JM Jr. Surgical resection of third ventricle colloid cysts. Preliminary results comparing transcallosal microsurgery with endoscopy. J Neurosurg 1994;81(2):174–8. [53] Heikkinen ER, Heikkinen MI. New diagnostic and therapeutic tools in stereotaxy. Appl Neurophysiol 1987;50(1–6):136–42. [54] Fukushima T. Endoscopic biopsy of intraventricular tumors with the use of a ventriculofiberscope. Neurosurgery 1978;2(2):110–3. [55] Greenberg IM. Intraoperative ultrasonography with a cystoscope for the biopsy of a deep-seated brain lesion: case study. Neurosurgery 1986;19(1):49–58. [56] Otsuki T, Yoshimoto T, Jokura H, Katakura R. Stereotactic laser surgery for deep-seated brain tumors by open-system endoscopy. Stereotact Funct Neurosurg 1990;54–55:404–8. [57] Zamorano L, Chavantes C, Moure F. Endoscopic stereotactic interventions in the treatment of brain lesions. Acta Neurochir Suppl (Wien) 1994;61:92–7. [58] Cohen AR. Ventriculoscopic surgery. Clin Neurosurg 1994;41:546–62. [59] Jallo GI, Morota N, Abbott R. Introduction of a second working portal for neuroendoscopy. A technical note. Pediatr Neurosurg 1996;24(2):56–60. [60] Fries G, Perneczky A. Endoscope-assisted brain surgery: part 2—analysis of 380 procedures. Neurosurgery 1998;42(2):226–32.

[61] Cheng WY, Chang CS, Shen CC, Wang YC, Sun MH, Hsieh PP. Endoscope-assisted microsurgery for treatment of a suprasellar craniopharyngioma presenting precocious puberty. Pediatr Neurosurg 2001;34(5):247–51. [62] Abdullah J, Caemaert J. Endoscopic management of craniopharyngiomas: a review of 3 cases. Minim Invasive Neurosurg 1995;38(2):79–84. [63] Caemaert J, Abdullah J, Calliauw L. Endoscopic diagnosis and treatment of para- and intra-ventricular cystic lesions. Acta Neurochir Suppl (Wien) 1994;61:69–75. [64] Zamorano L, Chavantes C, Dujovny M, Malik G, Ausman J. Stereotactic endoscopic interventions in cystic and intraventricular brain lesions. Acta Neurochir Suppl (Wien) 1992;54:69–76. [65] Halves E, Bushe KA. Transsphenoidal operation on craniopharyngiomas with extrasellar extensions. The advantage of the operating endoscope [proceedings]. Acta Neurochir Suppl (Wien) 1979;28(2):362. [66] Ferrer E, Santamarta D, Garcia-Fructuoso G, Caral L, Rumia J. Neuroendoscopic management of pineal region tumours. Acta Neurochir (Wien) 1997;139(1):12–21. [67] Ellenbogen RG, Moores LE. Endoscopic management of a pineal and suprasellar germinoma with associated hydrocephalus: technical case report. Minim Invasive Neurosurg 1997;40(1):13–6. [68] Haw C, Steinbok P. Ventriculoscope tract recurrence after endoscopic biopsy of pineal germinoma. Pediatr Neurosurg 2001;34(4):215–7. [69] Liston SL, Siegel LG, Thienprasit P, Gregory R. Nasal endoscopes in hypophysectomy. J Neurosurg 1987;66(1):155. [70] Gamea A, Fathi M, el-Guindy A. The use of the rigid endoscope in trans-sphenoidal pituitary surgery. J Laryngol Otol 1994;108(1):19–22. [71] Rodziewicz GS, Kelley RT, Kellman RM, Smith MV. Transnasal endoscopic surgery of the pituitary gland: technical note. Neurosurgery 1996;39(1): 189–99. [72] Jho HD, Carrau RL. Endoscopic endonasal transsphenoidal surgery: experience with 50 patients. J Neurosurg 1997;87(1):44–51. [73] Heilman CB, Shucart WA, Rebeiz EE. Endoscopic sphenoidotomy approach to the sella. Neurosurgery 1997;41(3):602–7. [74] Aust MR, McCaffrey TV, Atkinson J. Transnasal endoscopic approach to the sella turcica. Am J Rhinol 1998;12(4):283–7. [75] Moreland DB, Diaz-Ordaz E, Czajka GA, Zugger CM. Endoscopic resection of pituitary lesions through the nostril. Semin Perioper Nurs 1998; 7(3):193–9. [76] Moses RL, Keane WM, Andrews DW, Goel R, Simeone F. Endoscopic transseptal transsphenoidal hypophysectomy with three-dimensional intraoperative localization technology. Laryngoscope 1999;109(3):509–12.

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[86] Wahlig JB Jr, Welch WC, Weigel TL, Luketich JD. Microinvasive transaxillary thoracoscopic sympathectomy: technical note. Neurosurgery 2000; 46(5):1254–8. [87] Vanaclocha V, Saiz-Sapena N, Panta F. Uniportal endoscopic superior thoracic sympathectomy. Neurosurgery 2000;46(4):924–8. [88] Chung HY, Seo CG, Lee SG. Video endoscopic sympathectomy using a fiberoptic CO2   laser to treat palmar hyperhidrosis. Neurosurgery 1993; 32(2):327–9. [89] Kao MC. Percutaneous radiofrequency upper thoracic sympathectomy. Neurosurgery 1997;40(1): 216–7. [90] Schaffer JL. Endoscopic discectomy. J Neurosurg 1994;81(6):965–6. [91] Adamson TE. Microendoscopic posterior cervical laminoforaminotomy for unilateral radiculopathy: results of a new technique in 100 cases. J Neurosurg 2001;95(1 Suppl):51–7. [92] Jho HD. Endoscopic transpedicular thoracic discectomy. J Neurosurg 1999;91(2 Suppl):151–6. [93] Karahalios DG, Apostolides PJ, Vishteh AG, Dickman CA. Thoracoscopic spinal surgery. Treatment of thoracic instability. Neurosurg Clin North Am 1997;8(4):555–73. [94] Frank E. Removal of a lateral disc herniation with malleable endoscopic forceps: technical note. Neurosurgery 1997;41(1):311–3. [95] Onik G, Richardson D, Amaral J, Jennings W, Sholes A. Percutaneous anterior discectomy under ultrasound guidance. Minim Invasive Neurosurg 1995;38(2):90–5.

Neurosurg Clin N Am 15 (2004) 9–17

The endoscopic management of arachnoidal cysts Rick Abbott, MDa,b,* a

Department of Neurosurgery, INN, Beth Israel Medical Center, 170 East End Avenue, New York, NY 10128, USA b Department of Neurosurgery, Albert Einstein School of Medicine, New York, NY, USA

Arachnoidal cysts are a not uncommon lesion for a neurosurgeon, particularly a pediatric neurosurgeon, to be called on to treat. In one autopsy series, the incidence of these cysts was 0.1% [1]. Of  lesions arising intracranially, arachnoidal cysts comprise approximately 1% [2]. There has been active debate as to how to manage these cysts best, with the controversy driven by their benign behavior, subtle clinical sequelae, and the potential for treatment failure or complications. Not surprisingly, the introduction of the neuroendoscope into a neurosurgeon’s armamentarium typically leads to the consideration of its use to treat these entities in the hope of accomplishing what a craniotomy can while avoiding the associated morbidity. In the following article, the wisdom of such an approach is explored. Pathology and pathogenesis

In 1831, Bright [3]  first described an arachnoid cyst as ‘‘. . .a serous cyst forming in connection with the arachnoid, and apparently lying between its layers. . .’’ In his book, he discussed two cases, stating that these cysts seemed to be chronic, to have a low potential for growth, and to be of sizes varying from that of a pea to as large as or larger than an orange. During the past century, these observations were confirmed with the introduction of microscopic neuropathology, and in 1978, Rengachary et al [4] published a photomicrograph illustrating Bright’s observation. This photomicro-

* Department of Neurosurgery, INN, Beth Israel Medical Center, 170 East End Avenue, New York, NY 10128, USA. E-mail address:   [email protected]

graph demonstrated splitting of arachnoidal membrane at the margin of the cyst and a lack of  trabecula within the cyst, showing the cyst to arise within the arachnoidal membrane and not within the subarachnoid space. The cyst membranes contained hyperplasic arachnoidal cells and a thick layer of collagen. The pathogenesis, however, has been more controversial. Until the 1970s, authors argued over arachnoid cysts being either secondary phenomena occurring in regions of agenesis of  the brain or primary events of dysgenesis of the arachnoid investing the brain. In 1955, Robinson [5]   published a series of 15 patients with middle fossa arachnoidal cysts, hypothesizing that they were cerebrospinal fluid (CSF) collections passively filling a space left by an agenesis of a portion of the temporal lobe. Starkman et al  [6]  put forth a countertheory in 1958 in a report of three autopsies done on individuals with middle fossa cysts, finding these cysts to be surrounded by arachnoidal membrane, which led him to conclude that the cysts had arisen as a result of  splitting or duplication of the arachnoid during development. With the introduction of CT scanning and the ability to image the brain before and after treatment of these cysts, it became apparent that there was a capacity for expansion of the temporal lobe into space provided by decompression of the cyst. In 1971, Robinson [2]  withdrew his hypothesis of agenesis, stating that the cysts were caused by maldevelopment of the arachnoid. Robinson [2], the primary proponent of these cysts being secondary phenomena, abandoned his position after observing that neurologic sequelae to these cysts were not in proportion to the cyst’s size and that brain re-expansion could be seen on CT after the cysts were treated.

1042-3680/04/$ - see front matter    2004 Elsevier Inc. All rights reserved. doi:10.1016/S1042-3680(03)00071-8

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Arachnoidal cysts typically arise within normal arachnoidal cisterns. They are believed to arise around week 15 of gestation after the rupture of  the roof of the closed fourth ventricle and creation of the foramina of Luschka and Magendie. This allows for the escape of CSF into the subarachnoid space, where it replaces intracellular ground substance filling the subarachnoid space. Duplication or splitting of the arachnoid at the time of cistern formation provides the anlage for the arachnoidal cyst. Similarly, splitting or duplication of the ependymal lining of the lateral ventricles results in the formation of intraventricular or ependymal cysts. Arachnoidal cysts most commonly arise in the middle fossa (30%–50%), but 10% arise on the hemisphere convexity, 10% in the suprasellar cistern, 10% in the quadrigeminal cistern, 10% in the cerebellopontine (CP) angle, and 10% in the midline of the posterior fossa  [7]. Intraventricular cysts typically arise in or near the atria of the lateral ventricles. Their walls can be formed by arachnoidal cells (intraventricular arachnoidal cysts), ependymal cells (ependymal cysts more correctly viewed as being periventricular), neuroepithelial cells, or choroidal cells. Most of these cysts, excluding the choroidal cysts, probably represent a dysgenic process and are therefore not uncommonly associated with dysfunction of adjacent brain parenchyma as manifested by focal seizures and cognitive disabilities [8]. Presentation

Intracranial CSF cysts typically become symptomatic in patients before the age of 20 years, with most doing so within the first decade  [9]. There is some variation in age at presentation according to the location of the cyst, however. Arachnoidal cysts of the middle fossa present in patients before the age of 16 years [10]. Cysts of the quadrigeminal cistern present earlier, usually by the age of 12 months because of their compression of the aqueduct of Sylvius [8], whereas arachnoidal cysts of the suprasellar cistern present later in childhood, with more than 60% presenting in patients between 1 and 20 years of age [8]. Only 14% of  suprasellar cysts present after the age of 20 years. The signs and symptoms at presentation are referable to the location and size of the cyst. With the exception of cysts of the CP angle, the most common symptoms present at presentation are those of a slowly growing mass or of hydrocephalus (ie, headache). The headache can be generalized, or it may localize to the site of the cyst.

Other symptoms at presentation point to the location of the cyst. Cysts of the middle fossa can be associated with partial or secondarily generalized seizures. Arai et al [11] found a 39% incidence in 77 patients having cysts of the middle fossa, whereas Ciricillo et al   [12]   found the same incidence in 39 patients. Boop and Teo   [13]   have reported that more than 80% of their patients with such cysts manifest behavioral abnormalities, attention deficit disorder, or other problems in school. Cysts of the quadrigeminal cistern can be associated with nystagmus, Parinaud’s syndrome, hearing disturbances, and, rarely, motor deficits. Such symptoms are rare because of the relatively early onset of hydrocephalus associated with such lesions. Suprasellar cysts can be associated with visual disturbances (papilledema, optic atrophy, or bitemporal field cuts), endocrinopathies, and the ‘‘bobble head doll’’ sign that is pathognomic for lesions in this location. Cysts of the CP angle typically have a long history of slowly evolving symptoms referable to stretching of cranial nerves and distortion of the cerebellum. Vertigo, hearing disorders (eg, tinnitus, hearing loss), hemifacial spasm, facial paresis, trigeminal neuralgia, decreased corneal sensation, nystagmus, intention tremor, ataxia, and dysmetria can be features of  these cysts. If ignored too long, obstruction of the outlets of the fourth ventricle can result in an obstructive hydrocephalus. Clival arachnoidal cysts distort the brain stem, causing compression of the corticospinal tracts (paresis in the extremities, hyperreflexia, and Babinski sign) and stretching of cranial nerves (diplopia). When these extend into the supratentorial space, endocrinopathies can evolve because of compression of the pituitary apparatus. Other than signs of increased intracranial pressure, intraventricular cysts can be associated with focal seizures, ataxia and other gait disturbances, blurred vision, or frank diplopia. Diagnosis

The imaging tool of choice with these cystic CSF lesions is MRI (Fig. 1). Cysts of the middle fossa, clivus, and CP angle must be differentiated from epidermoid cysts. Diffusion-weighted MRI is useful in such cases, because the two types of  cysts have different signal characteristics in the imaging sequence. Suprasellar arachnoid cysts need to be differentiated from craniopharyngiomas and Rathke cleft cysts. The suprasellar arachnoid cysts are typically larger; grow symmetrically and upward, resulting in the ‘‘Mickey

R. Abbott / Neurosurg Clin N Am 15 (2004) 9–17 

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Fig. 1. (A) Coronal T1-weighted MRI scan of middle fossa arachnoid cyst. (B) Axial T2-weighted scan of suprasellar arachnoid cyst’s base with flow void seen at point of fenestration (arrow). (C ) T2-weighted sagittal MRI scan of  quadrigeminal arachnoidal cyst. (D) T1-weighted coronal MRI scan of cerebellopontine angle arachnoidal cyst.

Mouse’’ sign; and do not contain calcification commonly seen in craniopharyngiomas. In this situation, CT may be warranted to exclude a craniopharyngioma given this modality’s sensitivity for calcium.

Intraventricular CSF cysts can be differentiated from epidermoids, dermoids, and parasitic cysts using MRI. The differential diagnosis should be discussed with your neuroradiologist when ordering imaging of the lesion.

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Treatment

The first question to be answered is that of  whether any treatment should be offered. Implied in this question is whether further growthof the cyst is expected and whether symptomatic hydrocephalus is present. The latter question is easily addressed by careful history taking and examination of the patient. The former canbe more difficult. There are few reports available that offer rules for treatment based on the observed natural history of  these cysts. One based on a retrospective study of  adults with arachnoidal cysts showed that cysts tended to grow over time if there was distortion of  neural structures adjacent to the lobe containing the cyst or to bony structures  [14]. This does not offer assistance in decision making for children, however, given its retrospective nature and the fact that because the study was conducted in a group of  adults, it represented a more benign subgroup of  patients with this condition. Most reports dealing with the pediatric population recommend treatment at the time of discovery of the cyst unless it is of a small size with minimal distortion of surrounding tissues and has been discovered incidentally [13,15,16]. Cysts that distort surrounding neural tissues have been shown to alter cerebral blood flow [10,17]. Presumably, this explains the atrophy that canoccur over time, as shown whenthere is a failure of parenchymal re-expansion when cysts are treated in older individuals. Next to be answered when treatment has been elected is how the cyst should be treated. In the 1980s, most articles discussing treatment of these cysts favored the use of shunts. Presumably, this was the result of a relatively high incidence of  postoperative complications after craniotomies in the 1960s and 1970s. As operative techniques and the use of microneurosurgery have evolved, a reduction in the incidence of postoperative complications has occurred. With this and a greater appreciation of the life history of a shunted patient, there has been a natural shift in preference from treating these cysts with shunts to surgical fenestration [18]. Theoretically, to fenestrate a cyst is to cure it; thus, a lifelong dependence on a shunt is avoided. This shift in preference toward fenestration is only being accelerated with the introduction of the endoscope. Endoscopic treatment of intracranial CSF cysts is technically challenging and should only be considered by experienced neuroendoscopists. The anatomy can be obscure, and the number and complexity of the instruments used are greater

than those used in the more standard neuroendoscopic cases, such as third ventriculostomy. To start, careful planning is required. Thought should be given to the trajectory taken to the target(s) for fenestration. This is especially critical when multiple fenestrations are being considered, as is the case with a suprasellar cyst, or when a third ventriculostomy is needed in addition to cyst fenestration, as is case with a quadrigeminal cyst. An incorrectly placed burr hole because of a poorly planned trajectory results in an injury to the cortical tissues surrounding the scope as it is rocked back and forth to reach fenestration targets. When grossly off, reinsertion of the guide cannula to reach a second target may not even be possible and a new burr hole might be required. Ideally, when the target abuts or is in a ventricle, it is best to approach it via the ventricle so that normal anatomic structures can be used for guidance. It can be difficult to visualize structures onthe other side of a cyst’s wall, and it is a common occurrence to punch holes into brain tissue when attempting to fenestrate a cyst to an adjacent CSF space. Thought should also be given to structures that are to be avoided during the introduction and advancement of the scope. Ideally, the trajectory should be established to avoid these structures. If  this is impossible, thought should then be given as to how to avoid their injury, such as establishing early visualization with the scope before encountering the structure so as to avoid injury (eg, visualization of the fornix at the foramen of Monro so as to avoid it as one traverses the foramen). Next to be considered is whether a selfretaining holder for the scope is to be used. The use of a self-retaining system adds time and complexity to the case. In many cases, an assistant can navigate the scope while the surgeon works with instrumentation through the scope. In this setting, the assistant should be experienced in the use of the scope and familiar with the working habits of the surgeon so that the two work as a fluid team. The surgeon cannot do an adequate  job if he or she is worrying about or fighting with the assistant. In such a setting, the surgeon might correctly elect to use a self-retaining system. The other setting where the use of such a system should seriously be considered is when one anticipates being at the target site for more than a few minutes because of the need for a delicate or extensive surgical dissection. Also, if one is considering the use of a second instrument channel, it is best to have the scope held by a self-retaining system.

R. Abbott / Neurosurg Clin N Am 15 (2004) 9–17 

With regard to the use of a second instrument channel, this refers to the introduction of a second catheter that approaches the target via a different trajectory than that of the endoscope [19]. It can be useful when one anticipates the need for instruments that are larger than the working channel of  the scope or when there is a need to view the working of the instruments from an angle. This can be useful when one anticipates pulling material out of the surgical field, because such a maneuver not uncommonly blinds the endoscopist as the material reaches the head of the scope. The surgeon also gains a greater appreciation of the amount of  distortion that occurs during the maneuvering of  the instrumentation. Use of the second channel does add another level of complexity to the case, however. First, there is the issue of capturing and maintaining visualization of the channel. This becomes increasingly difficult as the distance between the burr holes of the scope and instrument channel increases and as the depth of the target increases. Second, there can be difficulty in coordinating the manipulation of the two channels. This takes some practice, and my advice is to make small movements that do not result in the complete loss of visualization of the instrument channel. The instrument channel is first moved partially out of  the field of view in a desired direction, and the scope is then moved to recenter the instrument channel in its field of view. Computer-assisted guidance systems can be of great use in overcoming these problems, with trackers being placed on the scope as well as on the instrument channel. At every step in the surgery, absolute attention must be paid toward homeostasis. It has been established that less than a teaspoon of blood within the intraventricular fluid space blinds the endoscopist. Consequently, after the burr hole has been drilled and before the dura is opened, homeostasis must be complete. This is also the case after the dura is opened before penetrating the arachnoid. Midline cysts, such as suprasellar and quadrigeminal cysts, are typically approached via the ventricles. A guide sleeve is typically introduced into the lateral ventricle, its stylet is removed, and the endoscope is then advanced into the lateral ventricle. During this approach, it is wise to remain oriented to the trajectory of the scope so as to appreciate the general location of the scope’s tip. When the anatomy is disorienting, the first step should be to check that one’s conceptualization of  the scope’s trajectory is correct. More than once, I have mistakenly thought that I was in the region of  the foramen of Monro only to discover that the

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scope was pointing posterior with the tip in the ventricle’s atrium. This is especially common with a burr hole placed too anteriorly. Normal anatomic structures are searched for to further establish orientation. Once the choroid plexus is found, it can be followed anteriorly to find the foramen of Monro or posteriorly to point to where a quadrigeminal cyst is herniating through the floor of the lateral ventricle. If the scope feels awkward in its movement, the most common reason is that the camera is not oriented to the scope (ie, the camera’s 12-o’clock position is not the scope’s 12-o’clock position). The scope should be withdrawn from the head and its camera’s orientation checked. Laterally projecting cysts, such as those of the middle fossa and CP angle, are approached through the overlying parenchyma laterally. This parenchyma can be present to a varying degree. Draped over the surface of the cysts are cortical veins, especially in the case of cysts of the middle fossa. Schroeder et al   [20]   have suggested not disturbing the lateral wall of such cysts so as to avoid traction of cortical veins stretched over their surface. Once within these cysts, arterial vessels of  the Sylvian fissure can be seen coursing the medial wall. They can be followed down to the basilar cisterns, where the fenestrations can be made. The membrane of these cysts has been shown to be rich in collagen; consequently, it can be difficult to penetrate. Scissors or a knife can be used to cut an opening. It can then be enlarged with sharp dissection or by repeated inflation of a balloon. It has not been established what constitutes an adequate opening. Until such time as this has been established, one should attempt to duplicate what one would accomplish using microneurosurgery via a small craniotomy. If difficulty is encountered in doing this, judgment is used, but there should not be any hesitancy to convert to a craniotomy to accomplish one’s surgical goals. On more than one occasion, we have done this on our service; the families of our patients are always told that this is a possibility, and consent is obtained for just such a possibility. Earlier mention was made of the use of  computer-assisted surgical guidance systems or frameless stereotaxis. These systems can be of great use when working within cysts containing no anatomic landmarks for guidance. By using such systems, one moves from navigating by dead reckoning based on surface landmarks to imagebased navigation, where the tip of scope and or its channel or a second instrument channel can be seen

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on MRI or CT.Before performing the surgery, such systems can be used for surgical planning. Structures to be avoided can be incorporated in planning the trajectory, and this information is, in turn, used to establish the optimum location for the burr hole. Depending on the guidance system being used, there are several options that can be employed for image guidance. Some systems require the use of  dedicated pointing devices. In such settings, a special pointer can be manufactured to replace either the endoscope’s guidance sleeve or its stylet. Another alternative is to have the company modify a rigid endoscope so that its system can track it directly. I have preferred tracking the stylet of  a peel-away catheter used to establish a channel for the endoscope because it affords the greatest flexibility for scope selection and is the simplest and least expensive to manufacture. At least one system has removable tracking devices that can be attached to an instrument or catheter and then registered to the system to allow for tracking by the system. Some accuracy is sacrificed when using such a device, and it can take several minutes to

establish registration. Also, more than once, I have been unable to accomplish registration when attempting to use these attachable trackers. After registering the patient and pointing devices to the system, the burr hole is located using the system and the adequacy of the trajectory is confirmed before making a skin incision. It is wise to take several moments to confirm the appropriateness of instrument setup at this point so as to prevent discovering that movement of the scope is limited by something in the surgical field or tracking is lost when the scope is in a certain position within the head. Once this is done, the burr hole is made and the dura opened using the same care as mentioned previously. The appropriateness of the planned trajectory to the target is confirmed one final time using dead reckoning; the scope’s channel is then advanced toward the target. Advancement toward the target is done slowly while retaining the appropriate trajectory by maintaining it on at least two image planes ( Fig. 2). Some systems give a bird’s eye view or so-called ‘‘target view’’ showing the tip being tracked as well

Fig. 2. Image showing approach to target (marked with +) by outer sleeve of endoscopy (its tip is the point of the cross hairs). For this cyst, we were targeting the point where the cyst abutted the ambient cistern.

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as the target; this is quite helpful, because the goal is simply to overlay the two cross hairs. Side to side and upward or downward corrections in route to the target cause distortion in the brain’s parenchyma, because the catheter cannot slice through brain tissue. This is critical to appreciate when a flexible catheter for the scope is being used, because once the stylet is removed to allow for the introduction of the scope, the catheter deflects as the parenchyma restores itself to its resting configuration. The result is that the catheter tip will no longer be on target. Consequently, the surgeon must judge when there has been too great a need for correction of  trajectory. When there is concern about this, the catheter should be removed and a second attempt made to advance it to the target. Much has been made of the potential for brain shift imparting inaccuracy to the guidance data set as the surgery proceeds. Obviously, if one is to be working at only one target, this should not be of great concern if  things move along at a pace such that little CSF escapes before the catheter is on target. At the point that the scope is looking at the target, the accuracy of the guidance data set is no longer of  concern. Alternatively, if there is more than one target, thought should be given to the problem. In my experience, structures that are close to the center of the head and vertically inferior to my pointer seem to maintain accurate registration to the data set, whereas those near the surface or lateral to a deflating structure or lesion tend to lose registration as the case proceeds. This should be kept in mind when determining the order of  targeting. It is also important to remember that there is always a tomorrow and to discuss with a family member the possibility of needing multiple sessions to accomplish the surgical goal. There will be cases in which shunting of a cyst is required. We had one case of a quadrigeminal cyst that underwent three endoscopic fenestrations into the ventricles (twice into the lateral ventricle and once into the third) and two open fenestrations, only to fail all procedures and become symptomatic because of an increasing mass effect from the cyst (Fig. 3). It was then decided to insert a cystoperitoneal shunt. The placement of a catheter into an arachnoid cyst can be extremely difficult, because the cyst wall is extremely prone to deflecting the catheter to the side when insertion is attempted. Use of the endoscope to confirm entry into the cyst can avoid postoperative frustration. One can use a larger scope to cut a fenestration in the cyst wall. The scope and its guide sleeve are then advanced into the cyst, the

15

Fig. 3. Second recurrence of quadrigeminal cyst after two prior fenestrations into lateral and third ventricles. At the third operation, the cyst was fenestrated and a catheter placed for a cystoperitoneal shunt.

scope is removed, and a proximal catheter of  a cystoperitoneal system is then fed down the guide sleeve into the cyst. It is wise to determine the depth of scope insertion to establish the length of catheter needed before removal of the scope in such a setting and to use a peel-away guide sleeve to simplify catheter placement. Alternatively, a small intraluminal scope can be used as the catheter’s stint during attempted placement of the proximal catheter. Once within the cyst, the scope can be used to confirm cyst penetration. If the wall has not been penetrated, unipolar cautery can be applied to the scope to complete penetration unless there is concern about adjacent vessels, as might be the case for a quadrigeminal cyst. Before doing this, it is wise to back the scope out partially to visualize the wall better and confirm that it has indeed not been penetrated. On occasion, I have been fooled into thinking that I had not penetrated the cyst when, infact, I had,and I was simply upagainst the far wall of the cyst. In such a case, one can immediately see the interior of the cyst as opposed to a trailing cyst wall. Results

There are now a few papers describing outcomes in small series of patients who have undergone endoscopic management of their intracranial CSF cysts. Paladino et al [21] described 6 of their patients treated endoscopically. One had

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R. Abbott / Neurosurg Clin N Am 15 (2004) 9–17 

a parasagittal cyst, and the other 5 had middle fossa cysts. Four of 6 cysts were successfully managed endoscopically, with 2 others requiring insertion of a cystoperitoneal shunt. Kim   [22] reported on 7 patients with arachnoid cysts. Three had cysts in the posterior fossa, 2 had cysts in the suprasellar cistern, 1 had a cyst in the middle fossa, and 1 had a cyst on the convexity, with all experiencing symptomatic resolution. Radiographically, 4 of 7 cysts diminished in size, whereas 3 of 7 disappeared. Ruge et al   [23] reported on successfully managing 2 children with quadrigeminal plate cysts endoscopically, and Furuta et al [24] reported a similar case managed successfully using an endoscope to place a cystoperitoneal shunt after a failed attempt to place the catheter stereotactically. Brunori et al   [25] and Hayashi et al   [26]   have reported experiences similar to those of Ruge et al  [23]  in successfully communicating quadrigeminal cysts to the ventricles. Hopf and Perneckzy   [27]   reported on 36 patients with various forms of arachnoid cysts treated endoscopically, with 26 improving symptomatically. Wagner et al   [28]   reported on 2 children with arachnoid cysts managed successfully endoscopically, and Decq et al  [29] reported on 2 children with suprasellar arachnoid cysts successfully managed. Walker et al   [30]  reported a 64% success rate in managing 14 children with arachnoidal cysts endoscopically. In summary, as series numbers increased, so did failures, with larger series reporting around a 33% failure rate in endoscopically managing arachnoid cysts. This compares with a 30% failure rate for shunted cysts and a 19% failure rate in cyst fenestration in the European Cooperative Study [9]. The more aggressive cyst resection surgery had a 7% failure rate in the same study. Fewel et al   [18]  reported a 27% failure rate in 102 arachnoidal cysts managed with either surgical fenestration or resection. Undoubtedly, there is a learning curve associated with this technique, and the failure rate currently being seen in the endoscopically managed cases will lessen over time. Until such time as the failure rate duplicates that seen with open surgery, thoughtful consideration should be given to the adequacy of the fenestration accomplished endoscopically and to whether or not the procedure should be converted to an open operation if there is concern about its adequacy. Additionally, a frank discussion should be undertaken with the family as to the pros and cons of the various approaches so that they can make an informed decision.

Complications

As with any surgery, there are potential complications when endoscopically managing arachnoid cysts. ‘‘Minimally invasive’’ should not be construed to mean minimal risk by the surgeon, and the family or patient should in no way be sold a bill of goods that this technique has fewer risks than open surgery. Kim [22] reported that 1 of his 7 patients treated endoscopically experienced significant bleeding during her surgery, requiring abandonment of the endoscopic procedure with conversion to an open procedure with successful control of the hemorrhage and completion of the surgical goal of fenestration. Hopf and Perneczky [27] reported a 14%complication rate in imaging 36 patients with arachnoidal cysts. Four patients experienced subdural hematomas or hygromas after their surgery, with 2 of them also developing meningitis. This may be an important observation, because we have noted infections in some of our patients who have experienced intraoperative hemorrhaging, which required extraventricular drainage after surgery. This is a discussion we have with all our families before surgery. Another of the patients reported on by Hopf and Perneczky  [27] experienced hemorrhaging after treatment of a posterior fossa cyst, resulting in hydrocephalus that required a subsequent third ventriculostomy. Robinson and Cohen warn of the risks of injuring blood vessels and other structures by the guide sleeve when advancing the scope because of the sleeve not being visualized by the scope [8]. Finally, structures can be injured during the actual fenestration process when visualization is poor or excessive force is used to penetrate the tough membrane. Summary

I have little doubt that most arachnoidal cysts will be managed endoscopically in the future given the advances we have seen over the last decade in our instrumentation. Our excitement to employ this new technology should be governed by the reality that we are still learning and that our current success rate is not quite as good as what can be expected when using microneurosurgery. References [1] Shaw C, Alvord EJ. Congenital arachnoid cysts and their differential diagnosis. In: Vinken P, Bruyn G, editors. Handbook of clinical neurology, vol. 31. Congenital malformations of the brain. Amsterdam: North Holland; 1977. p. 75–136.

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[2] Robinson R. Congenital cysts of the brain: arachnoidal malformations. Prog Neurol Surg 1971;4: 133–74. [3] Bright R. Reports of medical cases, selected with a view of illustrating the symptoms and cure of  diseases by a reference to morbid anatomy, vol. 2. Diseases of the brain and nervous system. London: Lonham, Rees, Orme, Brown, Green, and Highley; 1831. [4] Rengachary S, Watanabe I, Brackett C. Pathogenesis of intracranial arachnoid cysts. Surg Neurol 1978;9:139–44. [5] Robinson R. The temporal lobe agenesis syndrome. Brain 1964;87:87–106. [6] Starkman S, Brown T, Linell E. Cerebral arachnoid cysts. J Neuropathol Exp Neurol 1958;17:484–500. [7] Hogg J, Peterson A, El-Kadi H. Imaging of cranial and spinal cerebrospinal fluid collections. In: Kaufmann H, editor. Cerebrospinal fluid collections. Park Ridge, IL: American Association of  Neurological Surgeons; 1998. p. 19–57. [8] Kaufmann H, editor. Cerebrospinal fluid collections. Park Ridge, IL: American Association of  Neurological Surgeons; 1998. [9] Oberbauer R, Haase J, Pucher R. Arachnoid cysts in children: a European cooperative study. Childs Nerv Syst 1992;8:281–6. [10] Boop F, Young R, Scott R. Arachnoid cysts of the middle cranial fossa and convexity. In: Kaufmann H, editor. Cerebrospinal fluid collections. Park Ridge, IL: American Association of Neurological Surgeons; 1998. p. 67–96. [11] Arai H, Sato K, Wachi A, Okuda O, Takeda N. Arachnoid cysts of the middle cranial fossa: experience with 77 patients who were treated with cystoperitoneal shunting. Neurosurgery 1996;39(6): 1108–12. [12] Ciricillo S, Cogen PH, Harsh GR, Edwards MS. Intracranial arachnoid cysts in children. A comparison of the effects of fenestration and shunting. J Neurosurg 1991;74:230–5. [13] Boop F, Teo C. Congenital cysts. In: McLone D, editor. Pediatric neurosurgery. Philadelphia: WB Saunders; 2001. p. 489–98. [14] Becker T, Wagner M, Hofmann E, Warmuth-Metz M, Nadjmi M. Do arachnoid cysts grow? A retrospective CT volumetric study. Neuroradiology 1991;33:341–5. [15] Artico M, Cervoni L, Salvati M, Fiorenza F, Caruso R. Supratentorial arachnoid cysts: clinical and therapeutic remarks on 46 cases. Acta Neurochir (Wien) 1995;132:75–8. [16] Galassi E, Gaist G, Giuliani G, Pozzati E. Arachnoid cysts of the middle cranial fossa:

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experience with 77 cases treated surgically. Acta Neurochir Suppl (Wien) 1988;42:201–4. De Volder A, Michel C, Thauvoy C, Willems G, Ferriere G. Brain glucose utilisation in acquired childhood aphasia associated with a Sylvian arachnoid cyst: recovery after shunting as demonstrated by PET. J Neurol Neurosurg Psychiatry 1994;57: 296–300. Fewel M, Levy M, McComb J. Surgical treatment of 95 children with 102 intracranial arachnoid cysts. Pediatr Neurosurg 1996;25:165–73. Jallo G, Morota N, Abbott R. Introduction of a second working portal for neuroendoscopy. A technical note. Pediatr Neurosurg 1996;24:56–60. Schroeder H, Gaab M, Niendorf W. Neuroendoscopic approach to arachnoid cysts. J Neurosurg 1996;85:293–8. Paladino J, Rotim K, Heinrich Z. Neuroendoscopic fenestration of arachnoid cysts. Minim Invasive Neurosurg 1998;41:137–40. Kim M. The role of endoscopic fenestration procedures for cerebral arachnoid cysts. J Korean Med Sci 1999;14:443–7. Ruge J, Johnson R, Bauer J. Burr hole neuroendoscopic fenestration of quadrigeminal cistern arachnoid cyst: technical case report. Neurosurgery 1996;38:830–7. Furuta S, Hatakeyama T, Nishizaki O, Fukumoto S. Usefulness of neuroendoscopy in treating supracollicular arachnoid cysts—case report. Neurol Med Chir (Tokyo) 1998;38:107–9. Brunori AA, Chiappetta F. Endoscopy for cysts. J Neurosurg 1999;91:1067–8. Hayashi N, Endo S, Tsukamoto E, Hohnoki S, Masuoka T, Takaku A. Endoscopic ventriculocystocisternostomy of a quadrigeminal cistern arachnoid cyst. Case report. J Neurosurg 1999;90:1125–8. Hopf N, Perneczky A. Endoscopic neurosurgery and endoscope-assisted microneurosurgery for the treatment of intracranial cysts. Neurosurgery 1998; 43:1330–7. Wagner HJ, Seidel A, Reusche E, Sepehrnia A, Kruse K, Sperner J. A craniospinal enterogenous cyst: case report. Neuropediatrics 1998;29:212–4. Decq P, Brugieres P, Le Guerinel C, Djindjian M, Keravel Y, Nguyen JP. Percutaneous endoscopic treatment of suprasellar arachnoid cysts: ventriculocystostomy or ventriculocystocisternostomy? Technical note. J Neurosurg 1996;84:696–701. Walker M, Petronio J, Carey C. Ventriculostomy. In: Cheek W, Marlin A, McLone D, editors. Pediatric neurosurgery: surgery of the developing nervous system. Philadelphia: WB Saunders; 1994. p. 572–81.

Neurosurg Clin N Am 15 (2004) 19–31

Basic principles and equipment in neuroendoscopy Vit Siomin, MDa, Shlomi Constantini, MD, MScb,* a

Department of Neurosurgery, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA Division of Pediatric Neurosurgery, Dana Children’s Hospital, Tel Aviv Medical Center, 6 Weizman Street, Tel Aviv 64239, Israel 

b

A fool with a tool is. . . still a fool. Lars Leksell

The advent of neuroendoscopy has had a remarkable impact on the field of neurosurgery. Although the use of an endoscope to diagnose and treat various central nervous system (CNS) conditions, particularly those confined to the ventricular system, has been well recognized for years [1–7], the story of modern neuroendoscopy is just beginning. It has been attended by a number of remarkable breakthroughs in optical physics, technology, and instrumentation. Needless to say, understanding the basic physics and instrumentation underlying today’s endoscopes is essential for safe and successful work with these delicate instruments. This article presents a basic overview of the technology that literally brought light into the depths of contemporary neurosurgery. Today’s market is saturated with neurosurgical endoscopes, with many companies producing similar pieces of equipment. Any article attempting to comprehensively list the advantages and disadvantages of each endoscope on the market today will probably be somewhat outdated by publication because of the rapid progress in this field. This article therefore does not even attempt to provide a full list of all commercially available endoscopes with their descriptions. The authors simply intend to provide readers with a general overview of the selected endoscopes, including a brief explanation of their respective advantages and disadvantages.

* Corresponding author. E-mail address: [email protected] (S. Constantini).

A brief history of optics

Roots of the modern rigid endoscope Until the sixties, the optic chains in a lens system were constructed of small glass lenses interspersed with large air spaces. A British physicist named Hopkins realized that the total amount of light transmitted through an endoscope is proportional to the refraction index of the material used and that using more glass than air would increase the amount of light by a factor of  about 2. He restructured the lens system to consist of long glass lenses interspersed with small lens-like air spaces [3]. These ‘‘rigid rod lens scopes,’’ with their increased light transmission ability, form the basis of most modern endoscopic systems (Fig. 1). Further reduction in light loss is achieved through a special coating of the glass surfaces to minimize light reflection. Uncoated glass surfaces usually lose about 5% of their light through reflection. Because endoscopes consist of multiple glass lenses, the cumulative light loss can become significant. The solution is to coat the glass surface with an ultrathin layer of magnesium fluoride. This layer markedly decreases the reflection and improves the optic characteristics of endoscopes and cameras [3,8,9]. Understanding fiberoptics Before the sixties, endoscopists used miniature tungsten light bulbs inside the endoscopes. These bulbs had two disadvantages, however: the heat generated by the bulbs could easily burn tissues, and the bulbs could not emit blue light waves, so a red color would dominate the working field. Fortunately, fiberoptic cables were invented in the

1042-3680/04/$ - see front matter    2004 Elsevier Inc. All rights reserved. doi:10.1016/S1042-3680(03)00075-5

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Fig 1. Conventional and rod lens systems.

sixties, a major breakthrough for endoscopic technology. With their development, the light source could be separated from the endoscope and its emitted lighted transmitted via fiberoptic cables to the tip of the endoscope. This avoided the problem of tissue injury from heat and also delivered a more natural light. Specialized cables could also be used to conduct images to a camera. Fiberoptic cables are made of individually coated flexible fibers with an inner core of silica glass. Fiberoptic bundles can be arranged in two ways [3]:   Coherently—the proximal end portrays the image exactly as it is perceived distally. A coherent arrangement is used for visualization during surgery.    Incoherently—fiber bundles transmit light only. An incoherent arrangement is used to transmit light to the surgical site. 

Most modern fiberoptic endoscopes contain a minimum of 10,000 coherent fibers. Some contain as many as 30,000 fibers. A greater number of fibers is an advantage, because the resolution of fiberoptic endoscopes is proportional to the number of fibers in the endoscope. More fibers provide an image with a much sharper resolution. Although a great number of fibers in bundles used to transmit images is an obvious advantage, it is not so gainful when it comes to transmission of light from the source box to the scope tip. Having many individual fibers bundled together in light source cables increases the total surface area and leads to a loss of 30% to 40% of the light being transmitted through all those individual fibers. Thus, contrary to popular belief, the light that emerges from the proximal tip is somewhat weaker than the light that enters the endoscope at the original source [3]. Light loss is discussed in greater detail later in this article in the section on light sources.

Working with optic angles The tip of the scope can be bent to different angles, bringing different aspects of the surgical field into view. These angles are obviously fixed in the rigid solid lens scopes as opposed to the flexible fiberoptic scopes, where the tip can be manually deflected to change the angle of view off the scope’s long axis. For the rigid solid lens scopes, the most commonly used angles are: 0 (‘‘head-on’’), 30 , 70 , and 120 . The 0 deflection scopes portray only what they are viewing head-on, minimizing the risk of disorientation. The angled scopes are more versatile in that they visualize areas that would otherwise be out of view or difficult to illuminate. The major disadvantage of angled scopes is that the indirect image may cause the surgeon to become disoriented. The authors encountered orientation difficulties mostly when operating on patients with congenital lesions, such as arachnoid and porencephalic cysts. Similar problems may also be encountered in endoscopically assisted transsphenoidal surgery and intracranial tumor removal. Steerability of fiberoptic endoscopes adds another element to the problem of disorientation. Extensive experience is necessary to get used to oblique and ‘‘around-the-corner’’ views. 

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Light sources

An endoscope’s light source is extremely important, often becoming a limiting or facilitating factor. Currently, most neurosurgeons use highintensity xenon light sources. The light is transmitted through incoherent fiber bundles to the surgical field. Setting the light source to between 300 and 500 W provides a superior picture quality. Other types of light sources, such as halogen, are not used in modern endoscopy because they do not generate a bright enough light.

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Light loss in a fiberoptic system is a significant issue. As a rule, 30% of light is lost at the lamp, because up to 30% of the surface area consists of  cladding and filler, which absorb and reflect light. Fiber mismatch (between the incoherent cable bundles and the coherent optic fiber bundles) accounts for another 20% loss. Significant loss also occurs because of mismatch between the wider transmitting cable and the thinner scopes used in neurosurgery. Additional light is also lost from inadvertent reflection in various surfaces. Thus, at best, only about 30% of the light generated within the light source reaches the distal tip of the scope  [3,8]. This problem is still awaiting a technologic solution. Cameras

The chip camera, or charged-coupled device (CCD), is a critically important part of any endoscopic system. Invention of the chip camera was a remarkable technologic achievement, allowing a significant decrease in the size of the endoscope combined with an improvement in the quality of the transmitted image in comparison with previously used tube cameras. Two kinds of CCDs are currently used in neuroendoscopy: the single-chip camera and the threechip camera. The principle used in chip camera technology is the same as in the microprocessor industry. The chips consist of horizontal and vertical photosensitive elements that are arranged in intersecting lines. The points of intersection correspond to pixels, or picture units, that appear on the display screen. Light reflected by the object being viewed hits each pixel, and a current is generated. Each pixel on the display appears either brighter or dimmer depending on the voltage of the current signal sent to that pixel. The voltage is a function of the brightness of the image being portrayed: a brighter point on the original object being viewed generates a higher voltage current, triggering a brighter image on the display screen. The exact current voltage sent to each point is not  just an approximation or estimate; it is actually a precise numeric representation of the energy generated when light hits the horizontal and vertical matrix of the camera. A digital image incorporating a complete set of picture units (pixels) is stored in the camera’s memory [8]. Most endoscopic systems now use single-chip cameras. A good resolution for neuroendoscopy is available with 0.5-in cameras. When the resolu-

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tion of the one-chip camera is not enough, the image may be computer enhanced. Three-chip cameras provide better picture quality. The authors use the David-3-Chip-Camera from Aesculap (Center Valley, Pennsylvania), which features a resolution of more than 800 horizontal lines, compared with 500 lines in the standard 0.5-in micro-lens-on-chip technology camera (Fig. 2). The improved image of the three-chip camera comes at a price, however—a somewhat larger camera size and higher cost. Video monitors

The monitor is an integral part of every endoscopic system (Fig. 3). Three things should be considered in selecting a monitor: resolution, screen size, and cost. A higher resolution monitor provides better picture quality. There is no advantage to a monitor resolution that is significantly better than the camera resolution, however, because the monitor only displays the image seen and processed by the camera. The monitor cannot improve the camera’s image. By the same token, a top-quality image from the highest resolution camera must still be displayed on the monitor, so a lower resolution monitor ruins even the best camera image. When choosing the screen size, remember that the camera output is displayed over an area significantly larger than the cross section of the optic cable. As an image is enlarged, the image resolution and quality decrease. Screens larger than 13 in display poorer quality images because of reduced resolution. This becomes even a greater problem with images generated with a fiberoptic scope. The pixels that are only slightly visible

Fig 2. 3-chip CCD camera (Aesculap, Center Valley, Pennsylvania).

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Fig 4. 15F‘‘peel-away’’ blunt andtaperedtip introducers.

Fig 3. 100Hz monitor (Sony, New York, New York) and 3-chip CCD camera (Aesculap, Center Valley, Pennsylvania).

when fiber scopes with reasonable resolution are transmitted to a screen smaller than 13 in undergo magnification with consequent enlargement of pixels when projected to larger screens. Conversely, larger screens are useful for displaying multiple images. Finally, note that it is often most costeffective to purchase a monitor from the manufacturer that supplies the rest of the system. Endoscopic components and tools

Peel-away catheter Because the concept of minimally invasive surgery lies at the heart of neuroendoscopy, every stage of the procedure, from cannulation of the fluid space to exit, should minimize interference with the patient’s anatomic structures. During an endoscopic procedure, the surgeon may need to insert and remove the scope many times. It is therefore logical to create a single ‘‘safe passageway’’ that allows multiple reinsertions of the scope along the same tract without jeopardizing surrounding brain. Most surgeons today use disposable peel-away catheter introducers (eg, those manufactured by

Cook [Cook Critical Care, Bloomington, IN] or Neuroview [Integra NeuroSciences, Plainsboro, NJ]). These may be attached to the scalp or drapes with Steri-strips (3M Health Care, St. Paul, MN) or staples. Both tapered and blunt-tip catheters are available (Fig. 4). The catheter is supplied in various diameters ranging from number 3 to number 49 French. The most popular sizes in neuroendoscopy fall between number 10 and number 20 French. Number 10 French catheters are appropriate for 2- to 4-mm diameter endoscopes, whereas number 20 French catheters are good for the larger 6- to 8-mm endoscopes. Larger diameter introducers are not used in neuroendoscopy. The disadvantage of using a peel-away introducer is that it can cause bleeding because of  injury to the choroid plexus or intraventricular veins on insertion. Unfortunately, only Neurocare’s (Integra NeuroSciences, Plainsboro, NJ) number 9 French catheter has centimeter markings. Therefore, the authors have found it helpful to apply some bone wax 5 cm from the tip of the introducer to prevent unnecessarily deep insertion of the catheter and damage to intraventricular structures. Alternatively, one can use an obturator/operating sheath. This is a reusable metal pipe that can only be attached with a scope holder, which can be a slight inconvenience. The introducers and the sheath enable multiple reinsertions of an endoscope without repeated recannulations. Rigid endoscopes Most neurosurgeons today still use rigid glass endoscopes that are neither flexible nor steerable. An advantage of rigid rod lens scopes is that

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smaller diameter lenses may be used, allowing the endoscope designer to either decrease the diameter of the whole scope, producing a smaller and more delicate instrument that can reach more inaccessible areas, or add more space to the working channel, producing an instrument that can accomplish many tasks for the surgeon. The basic rigid glass endoscope consists of three elements: an optic system, a working channel, and an irrigation port (Fig. 5).   Table 1  summarizes the features of the most common rigid endoscopes. The remainder of this section discusses the advantages and disadvantages of typical endoscopes available from various manufacturers. 

The Gaab Neuro-Endoscope (K. Storz, Tuttlingen, Germany) has a 6.5-mm operating sheath, with a 3-mm working channel. Fiberoptic light transmission is incorporated. The Gaab endoscope with a 2-mm operative Hopkins telescope is a popular choice for surgery because it allows visualization during surgical instrumentation with specially designed rigid instruments. The 4-mm 0 , 30 , 70 , and 120 diagnostic scopes are popular for diagnostic orientation in the ventricular system, basal cisterns, arachnoid cysts, or cystic tumors. Because these diagnostic scopes do not have a working channel, they have room for larger diameter lenses and are therefore able to provide exceptionally clear visualization and orientation. Note that Codman & Shurtleff (Johnson & Johnson, New Brunswick, NJ) also manufactures the Gaab Neuro-Endoscope. The outer diameter of the Codman & Shurtleff endoscope is only 

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5.8 mm, however, and the diameter of the working channel is 1.6 mm.   The Chavantes–Zamorano Neuro-Endoscope (K. Storz) has a relatively large outer diameter of 8 mm. It has one central 3-mm working channel and two separate suction and irrigation channels, which can also be used for flexible instruments. Better visualization can be achieved with the smaller diameter 30 and 70 diagnostic scopes. This endoscope also has a manometer for constant monitoring of intracranial pressure during surgery. The disadvantage of the ChavantesZamorano system is that the scope has a relatively large diameter and the overall size impedes maneuverability. Nevertheless, many neurosurgeons use this endoscope, especially for evacuation of intracerebral and, particularly, intraventricular hematomas, in conjunction with stereotaxy. Note that Codman & Shurtleff also manufactures the Chavantes-Zamorano endoscope. The difference is that the diameter of that endoscope’s working channel is 1.9 mm.    The Auer Neuro-Endoscope (K. Storz) has an outer diameter of 6.6 mm. This endoscope features two working channels: a straightforward 0 telescope that is 2.9 mm in diameter and an adapter for a Greenberg retractor. The larger size of the Auer endoscope is a major disadvantage; however, the excellent optics and specially positioned irrigation and suction apertures at the tip of  the endoscope facilitate a clear view of the field.   The Decq Neuro-Endoscope (K. Storz) comes in two models. The 3.5-mm  5.2-mm model is suitable for rigid or flexible instruments of  1.7 mm in diameter. The 4.0-mm  7.0-mm model is suitable for instruments of up to 3 mm in diameter. The telescope uses the Hopkins lens system with a 30 angle of  vision.  Aesculap produces an endoscope with a 6.2-mm operating cannula (Fig. 6). This model includes a 2.2-mm working channel, one diagnostic endoscope channel, one irrigation channel, and one overflow channel. This endoscope is available in two lengths: 250 mm, which is compatible with stereotactic frames, and 160 mm. The major advantage of this scope is excellent image quality; however, the large size is a limiting factor. 

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Fig 5. 3.2 mm rigid endoscope (K. Storz, Tuttlingen, Germany).

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Table 1 Basic features of rigid endoscopes

Endoscope

Outer diameter

Neuroview 700R (NeuroNavigational)

5.6 mm

Aesculap

6.2 mm

MINOP (Aesculap)

3.2 mm 4.6 mm

6.0

Gaab endoscope (Storz/Codman & Shurtleff)

6.5 mm (5.8 mm)

Chavantes-Zamorano (Storz/Codman)

8.0 mm

Auer endoscope (Storz)

6.6 mm

Decq endoscope (Storz)

Oval 3.5  5.2 mm

Oval 4.0  7.0 mm



Diameter of  working channels

Angles of  diagnostic scopes

1 working 1 irrigation 1 overflow 1 scope 1 working 1 irrigation 1 overflow 1 scope

2.0 mm

0 , 30 , 70

2.8 mm 2.2 mm

0 , 30

1 working/scope 1 working/scope 1 irrigation 1 overflow 1 working 1 irrigation 1 overflow 1 scope 1 working 1 irrigation 1 overflow 1 scope 1 working/scope 1 irrigation 1 overflow

2.8 mm 2.8 mm

Channels

2 working 1 irrigation 1 overflow 1 scope

1/2 working 1 irrigation 1 overflow 1 scope 1/2 working 1 irrigation 1 overflow 1 scope

  The MINOP Neuroendoscopy System (Aesculap) includes the following (Fig. 7):    Trocars with three different shaft diameter options. The 3.2-mm model has one optic/working channel. The 4.6-mm model has three optic/working, irrigation, and







Remark/clinical use 



2.7 mm 0 , 30 



Glass rod optics, Good image, Quite thick and heavy Glass rod optics, Good image, Quite thick and heavy, Good for stereotaxy Glass rod optics, Good image, Short, maneuverable

2.2 mm

2.8 mm 3.0 mm (4.0 mm)

3.0 mm (1.9 mm)

0 , 30 , 70 , 120 





0 , 30 , 70 



0



3.0 mm

1.7 mm



30





Glass rod optics, Good image, Quite thick and heavy Glass rod optics, Good image, Quite thick and heavy, Features manometer for ice intracranial measurement, Good for evacuation of  hematomas Glass rod optics, Good image, Quite thick and heavy, Adapter for Greenberg retractor Glass rod optics, Good image

3.0 Glass rod optics, Good image, Quite thick and heavy

overflow channels. The 6.0-mm model has four optic/working, additional working, irrigation, and outflow channels.    2.7-mmendoscopesthat are angledto 0 and 30 . These are suitable for freehand surgery as well as for fixation by the scope holder. 



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V. Siomin, S. Constantini / Neurosurg Clin N Am 15 (2004) 19–31

Fig 6. 6.2 mm rigid endoscope (Aesculap, Center Valley, Pennsylvania).

  Rigid instruments and electrodes    Good image quality; they are suitable for ‘‘pure’’ ventriculostomy, endoscopic surgery, or endoscope-assisted microsurgery: 

 Rigid wide-angled endoscopes for endoscopeassisted cranial neurosurgery; 0 , 30 , and 70 angles of view are also available from Aesculap.    The ‘‘classic’’ model Neuroview rigid scope, produced by NeuroNavigational (Integra NeuroSciences, Plainsboro, NJ), offers superior imaging characteristics. The outer diameter of the scope is 5.6 mm, with a 2.0-mm working channel, irrigation and aspiration ports, and a 2.8-mm scope channel. The scopes are 2.7 mm in diameter and are available with 0 , 30 , and 70 offset angles, providing 80 of view. 











occurring during endoscopic procedures. Finally, because of natural wear and tear of the optical components, the image quality deteriorates after prolonged use. It was thus inevitable that disposable endoscopes would be introduced into practice. Note, however, that disposable rigid endoscopes do not use a rigid lens optic system, because rigid lenses require a larger diameter. Instead, a 10,000to 30,000-pixel fiberoptic system is used. The quality of an image obtained through multipixel fiberoptic bundles is still significantly lower than that obtained with rigid lenses. Conversely, with disposable scopes, the surgeon receives a brand new set of optical components each time, which eliminates the problem of wear and tear. Fiberoptic endoscopes





Despite higher image quality, the classic design multiple-use scopes have some disadvantages. First, because the camera is directly attached to the scope, they are quite heavy and cumbersome. Second, the classic scopes are thicker, leaving larger holes in the brain. Third, there is a significant risk of cross-contamination. Many surgeons, unfortunately, are familiar with bouts of postoperative infections secondary to cross-contamination

This section discusses the flexible and rigid fiberoptic neuroendoscopes produced by a few different companies. Table 2 compares the advantages and disadvantages of rigid versus flexible endoscopes. Several types of flexible scopes are available from Aesculap:   A steerable scope with an outer diameter of  3.9 mm. This scope has a 1.1-mm working channel and a 0.5-mm suction channel. Unidirectional steerability allows 160 turns.    A steerable scope with an outer diameter of  2.9 mm. This scope does not have a working channel. Although this scope is mainly used for inspection purposes, a steerability of 140 up and down makes this a reasonable choice for dissection.    A series of nonsteerable flexible endoscopes with outer diameters ranging from 0.7 to 2.3 mm. None of them, except the 2.3-mm scope (see section on syringomyeloscope), have working channels. This group of endoscopes is usually used for endoscopic inspection, endoscopy-assisted surgery, or passing through a shunt. These nonsteerable endoscopes are superior to disposable flexible scopes in image quality because they use higher pixel optical fibers. 





Fig 7. 4.6 mm rigid endoscope (Minop, Aesculap, Center Valley, Pennsylvania).

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V. Siomin, S. Constantini / Neurosurg Clin N Am 15 (2004) 19–31

Table 2 Comparison of rigid and flexible scopes

Advantage’s

Disadvantages



Rigid scopes

Flexible scopes

Better image Higher resolution Wider view Better color Better light transmission Light weight of disposable scopes Less maneuverable Not applicable in spine

Steerability Application in spine For some light weight, because camera not attached to scope

Poor image Pixel granules Narrower view Less true color Worse light Smaller working channel Limited selection of scopes and instruments

 Aesculap produces another endoscope originally designed by Perneczky. This instrument is able to ‘‘look around the corner’’ while operating with the microscope. The Perneczky endoscope consists of a fiberoptic scope encased in a rigid shaft with an 80 curved tip 1.4 mm in diameter. Using this curved tip, structures in the operating field that are hidden from direct microscopic view can be inspected. The Perneczky endoscope may be set into a desired position with a scope holder (see section on scope holders). 

Two types of flexible scopes are available from Codman & Shurtleff:   Codman & Shurtleff produces a steerable neuroendoscope that is similar to the 3.9-mm endoscope from Aesculap. Its outer diameter is 4 mm, with a 1-mm working channel that accepts several types of instruments and accessories. The distal viewing tip can be rotated 100 to 160 via a thumb control unit.    Codman & Shurtleff also produces the Epic microvision. The Epic microvision is a semiflexible endoscope 1.8 mm in diameter with a bayonet-like design. The angle of the scope can be changed by inserting it into more rigid cannulas with straight, 20 , or 45 angles. Such small scopes can be used for: 









 Better intraoperative visualization, particularly in conjunction with an operative microscope, when an ‘‘around-the-corner’’ view is required   Blunt perforation of membranes when the scopes themselves are used as dissecting and fenestrating tools 



  Endoscope-assisted shunt placement when they are easily passed through the ventricular catheter as described in the following section.

Other fiberoptic scopes options include: NeuroNavigational produces a few disposable flexible endoscopes with outer diameters of 1.2, 2.3, and 4.6 mm. These scopes feature a rigid design with 10,000 pixel optical fibers for fine image resolution. The camera is elongated and not directly connected to the endoscope body, which significantly decreases the weight of the instrument and makes its pencil-like body easy to handle. The 0.9-mm Neuroview Fiberscope is one of the thinnest endoscopes available today. The 1.2-mm scope has only irrigation channels and is designed to fit into the lumen of shunt catheters. The 1.5-mm scope has a 0.49-mm working channel, and the 2.3-mm scope has a 1-mm working channel and a deflected tip, which improves maneuverability and access in confined areas. The 4.6-mm scope has two working channels.    A few lightweight endoscopes are offered by Clarus (Minneapolis, MN), including the rigid fiberoptic Channel endoscope. It is quite light and can be held as a pen (Fig. 8). The Channel endoscope is available in two lengths: 13.0 and 21.6 cm. The working channels may be either 3.15 or 2.15 mm in diameter. Irrigation is available through the irrigation port, with outflow through the working channel. Other fiberoptic endoscopes from Clarus include the MurphyScope and 

V. Siomin, S. Constantini / Neurosurg Clin N Am 15 (2004) 19–31

27

improve the surgical outcome once the surgeon is within the ventricle, because no specific place within the ventricle has been proven superior to any other [5]. Syringomyeloscope

Fig 8. Light-weight fiberoptic endoscope Minneapolis, MN).

(Clarus,

the NeuroPen (designed for shunt insertion). Three variants of the MurphyScope are available: 2.3-mm scopes with a bayonet-like malleable 40 angle, a straight 50 curved endoscope, and a 1.4-mm curved malleable scope. 



Comparison of rigid and flexible endoscopes Rigid and flexible endoscopes each have advantages and disadvantages. Table 2 highlights some of the pros and cons of each. Endoscopes for shunt placement It has been hypothesized that the use of a smalldiameter endoscope as a stylet within the ventricular catheter may allow more accurate catheter positioning within the ventricle, which should decrease the number of proximal shunt malfunctions and revisions   [5,10]. This theory has never been proven. Nevertheless, several types of fiberoptic endoscopes are commercially available for ventricular catheter placement. NeuroNavigational, Clarus, Cordis (Miami, FL), and Codman (Johnson & Johnson, New Brunswick, NJ) all produce semirigid lightweight scopes that have 10,000 optic fibers, providing adequate visualization of intraventricular structures. The NeuroNavigational 1.2-mm Neuroview endoscope, a disposable unit, can be used in conjunction with several ventricular catheter modifications, such as the commonly used Innervision catheter from PS Medical (Goleta, CA). The Neuroview endoscope can be used as a stylet to insert the catheter. Note that although using this technique to insert the catheter may decrease the possibility of completely missing the ventricle, it does not necessarily

Endoscopes can be used in surgical treatment of syringomyelia. Aesculap produces a flexible syringomyeloscope with an outer diameter of 2.3 mm. This scope has a working channel 1 mm in diameter, which may be suitable for 400- lm laser fibers. This endoscope is mainly used for intracavity inspection and dissection after the lesion is accessed via a laminectomy. A syringomyeloscope may also be useful in the treatment of chronic subdural hematomas. Coagulation Good hemostasis is essential in neuroendoscopy for adequate visualization of structures as well as safety. Hemostasis is achieved either with cautery systems (monopolar or bipolar) or with lasers (discussed in the next section). Monopolar cautery is the most direct and commonly used method to achieve hemostasis (Fig. 9). The Bugbee Wire (USA) is probably the simplest monopolar cautery, commonly used by urologists as well as neuroendoscopists. The Bugbee Wire without applied cautery current can also be used as a probe to ‘‘feel’’ tissue or membrane (eg, ‘‘palpation’’ of the floor of the third ventricle before fenestration) or to pierce a membrane (eg, third ventriculostomy, fenestration of cyst).

Fig 9. Various coagulation probes.

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Slightly more sophisticated monopolar cauteries are available from Cook and Codman & Shurtleff. The Cook system is a number 3 French retractable instrument that is kept within a protective sheath while passing through the working channel. The surgeon squeezes the loop handle to expose the tip as needed. Both round ball and pencil-point tips are commercially available. The Cook electrodes may be used through rigid and flexible endoscopes. Codman & Shurtleff designed the Micro Endoscopic Electrode (ME2), which relies on a retraction mechanism similar to the Cook cautery. Because there can be a problem with standard monopolar cauteries of burnt tissue adhering to the tip of the instrument, Heilman and Cohen  [2] invented the ‘‘saline torch’’ monopolar cautery. With this tool, the electric current is directed through a jet of saline, allowing the surgeon to dissect and coagulate structures without direct contact, even when completely immersed in cerebrospinal fluid (CSF). Bipolar coagulation is a more precise way of  achieving hemostasis with less scatter of current compared with a monopolar cautery. The simplest bipolar electrode is a fork electrode (eg, Aesculap 2.1-mm fork electrode). When using a fork electrode, however, the surgeon cannot pick up tissue, which makes its use somewhat limited. Codman & Shurtleff therefore introduced grasping bipolar forceps 2.5-mm in diameter. These forceps are suitable for coagulation of vessels of  no more than 2 mm in diameter. NeuroNavigational offers both 1.0- and 2.4-mm flexible bipolar electrodes. They can be used through rigid and flexible scopes. An advantage of these electrodes is a built-in irrigating channel to decrease adherence of the tissue to the wires. Finally, Clarus manufactures a bipolar cautery that looks like a pencil and has a 30 tip angle. This allows the surgeon better visibility of the cauterized object.

Fig 10. Endoscopicmicrosurgical instruments(Aesculap, Center Valley, Pennsylvania).

occluded ventricular catheter overgrown by choroid plexus (Fig. 10).    Cup forceps, two- or three-pronged forceps, and flexible loop retrievals are designed to obtain tissue for biopsy. The design of these instruments facilitates removal or retrieval of  tissue fragments. Some of these instruments are intended for single use. Aesculap manufactures similar instruments in flexible and rigid variants. The malleable steering forceps are available from Clarus.    Another helpful instrument is the Fogarty balloon (Fig. 11). Usually surgeons use number 2 or 3 French catheters, depending on the diameter of the working channel. The Fogarty balloon is used by many surgeons to dilate the opening in the floor of the third ventricle during an endoscopic third ventriculostomy. The advantage of this technique is that the inflated balloon compresses



Instruments Various grasping forceps are commercially available from different manufacturers:   Cook produces flexible forceps designed for use through rigid and flexible scopes.   Rat tooth, alligator, and mouse tooth forceps can be used for dissection, enlargement of an opening, and pulling tissues. On a few occasions, the authors have used them with endoscopic scissors to cut and remove an 

Fig 11. Balloon catheters.

V. Siomin, S. Constantini / Neurosurg Clin N Am 15 (2004) 19–31

surrounding tissues, constricting bleeding vessels.    In the past few years, there have been case reports of accidental, often fatal, injuries to the vessels of the basilar artery bifurcation complex [6].   Recently, a new device for perforation of the floor of the third ventricle (‘‘no through perforator’’) was developed by Grotenhuis and became commercially available from Synergetics (USA). It consists of  a 3-mm thick hollow rod with a sharp cutting edge. After suction is applied, the floor of the third ventricle ‘‘jumps up’’ and sticks to the tip of the perforator, leaving the interpeduncular vessels below. The device is turned gently to create a round 3-mm diameter hole. The device seems to improve safety and lower the risks involved in perforation of the floor of the third ventricle. Lasers The laser beam is a form of energy used in surgery to cut, coagulate, vaporize, and dissect tissues. Its applications are quite similar to those of electricity; however, the nature of the laser is uniquely different from that of electricity. Laser is an acronym for light amplification by stimulated emission of radiation. Laser energy can be generated in a plasma tube by a powerful electromagnetic field. Application of this field to some type of gas molecules, such as carbon dioxide or argon, leads to their excitation. Electrons from the excited molecules start moving from one energy state to another. When these molecules drop from an excited to a resting state, a photon (a unit of energy that has a characteristic wavelength) is released. The release of a photon energy unit is called fluorescence. Once a photon hits a neighboring molecule, another photon is released, the wavelength of which is in phase with the first photon. This process, called stimulated emission, is self-perpetuating, because neighboring molecules continue to bombard each other with photons. The mirrors on both tips of the laser tube reflect the emitted photons, increasing the level of movement and energy within the tube until, finally, the beam emerges. On emergence, the beam has the following three features:  The beam is coherent, because all photons are released in the same phase.  The beam is monochromatic, because the material emits only a single wavelength. 



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  The beam is collimated, because the waves emerge parallel to each other.

As a result of these features, a lens is able to focus the light to a fine point, with an extremely high concentration of power density  [4,8]. Biologic effects of laser Application of laser to tissue causes an instantaneous increase in temperature, leading to vaporization of the extracellular fluid and explosion of the cell. Four concentric zones of impact appear as a result of the interaction between laser and tissue:   Central zone—no cells remain, only burnt debris.   Vacuolated cells zone—the tissue is composed of nonviable vacuolated cells that retain some structure.   Edematous zone—some cells in this area are dead, but most of the cells are viable with increased intracellular water content.    Reversible ultramicroscopic changes zone—  although no alterations are seen under light microscopy, some minor histochemical changes are present. 

The first two zones are irreversibly dead. The latter two zones are viable and recoverable [4]. Types of medical lasers Many lasers are available for clinical use, but only two are commonly used in neuroendoscopy because of their ability to work through water and transmit through the miniature fiberoptic cables: neodymium:yttrium-aluminum-garnet (Nd:YAG) and potassium-tetanyl-phosphate (KTP) [4,9,11,12]. Initially, lasers were popular in neuroendoscopy, especially to make the opening in an endoscopic third ventriculostomy   [12].   After a few instances of injury to the vessels in the interpeduncular fossa [6], however, laser use significantly declined for safety reasons. Nevertheless, the Nd:YAG laser and, especially, the KTP laser may be useful in endoscopic tumor removal and cyst fenestration. The tissue penetration of  the KTP laser is less than with the Nd:YAG laser; its visible light makes it easier to handle, and it is less dependent on the tissue pigmentation, which makes it suitable for dissection of colloid cysts. Scope holders Neuroendoscopy can be done either freehand by one or two surgeons (one navigating the scope

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V. Siomin, S. Constantini / Neurosurg Clin N Am 15 (2004) 19–31

Table 3 Advantages and disadvantages of a scope holder

Advantages

Disadvantages

Freehand

With rigid holder

More freedom of movement, particularly when configuration needs to be frequently or continuously changes (eg, tumor removal, inspection of  subarachnoid cisterns)

Surgeon has the use of both hands

More fatigue for surgeon Greater risk of accidental movements

and the other working with instruments) or using a rigid holder.   Table 3  describes the advantages and disadvantages of each technique. Today, there are many scope holders available, such as the Leyla self-retaining retractor, the flexible Greenberg retractor, the Neuroview Scope Holder, and the Unitrac pneumatic holder produced by Aesculap (Fig. 12). The authors have found the latter system particularly helpful, even when operating freehand, because the holder can be used as an easily adjustable hand rest. The

Minimizes accidental movements and tremor More static (inflexible) Inconvenient when frequent repositioning is needed

device uses the same pressurized gas that powers pneumatic drills. Summary

In sum, understanding some of the basic principles of endoscopy and awareness of available resources can potentially be of considerable help to experienced neurosurgeons as well as beginners in selection of the most appropriate tools for different procedures and making cost-effective choices when browsing through multiple commercial advertisements and purchasing new equipment. Although numerous advantages in science and industry have made it possible to offer a wide variety of neuroendoscopes and tools, we believe the major achievements in this field are yet to occur. This particularly refers to the development of smaller fiberoptic scopes with better image quality and three-dimensional endoscopes and to the invention of more efficient tools for endoscopic tumor removal with the same degree of  safety as in open surgery. References

Fig 12. Unitrac scope holder (Aesculap, Center Valley, Pennsylvania).

[1] Cohen AR. Endoscopic ventricular surgery. Pediatr Neurosurg 1993;19:127–34. [2] Heilman CB, Cohen AR. Endoscopic ventricular fenestration using a ‘‘saline torch.’’. J Neurosurg 1991;74:224–9. [3] Hulka JF, Reich H. Light: optics and television. In: Textbook of laparoscopy. Philadelphia: WB Saunders; 1994. p. 9–21. [4] Hulka JF, Reich H. Power: electricity and laser. In: Textbook of laparoscopy. Philadelphia: WB Saunders; 1994. p. 39–43. [5] Levy ML, Lavine SD, Mendel E, McComb JG. The endoscopic stylet: technical notes. Neurosurgery 1994;35:335–6.

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[6] McLaughlin MR, Wahlig JB, Kaufmann AM, Albright AL. Traumatic basilar aneurysm after endoscopic third ventriculostomy: case report [see comments]. Neurosurgery 1997;41:1400–4. [7] Mixter WJ. Ventriculoscopy and puncture of the floor of the third ventricle. Boston Med Surg J 1923;188:277–8. [8] Nobles A. The physics of neuroendoscopic systems and the instrumentation. In: Jimenez DF, editor. Intracranial endoscopic neurosurgery. Park Ridge, IL: American Association of Neurological Surgeons; 1998. p. 1–12. [9] Shiau JSC, King WA. Neuroendoscopes and instruments. In: Jimenez DF, editor. Intracranial endo-

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scopic neurosurgery. Park Ridge, IL: American Association of Neurological Surgeons; 1998. p. 13–27. [10] Theodosopoulos PV, Abosch A, McDermott MW. Intraoperative fiber-optic endoscopy for ventricular catheter insertion. Can J Neurol Sci 2001;28: 56–60. [11] Wharen REJ, Anderson RE, Scheithauer B, Sundt TM. The Nd:YAG laser in neurosurgery. Part 1. Laboratory investigations: dose-related biological response of neural tissue. J Neurosurg 1984;60: 531–9. [12] Wood FA. Endoscopic laser third ventriculostomy [letter, comment]. N Engl J Med 1993;329: 207–8.

Neurosurg Clin N Am 15 (2004) 33–38

The anatomy of the ventricular system David G. McLone, MD, PhD Children’s Memorial Hospital, 2300 Children’s Plaza, #28, Chicago, IL 60614, USA

An understanding of the form and detail of the ventricular system is an important point of  departure when beginning to learn neuroendoscopy. Knowledge of the form and detail allows planning of the optimal entry point to enable viewing desired structures. This information also acts as a road map to direct the endoscopist to targets. It is essential to know what is just beyond the structure at the tip of the scope. Pathologic processes, such as hemorrhage, ventriculitis, and hydrocephalus, may alter the appearance of the ependymal surface of the ventricle but usually do not alter structures needed to navigate the ventricular system. Obviously, knowledge of the function of structures within the field of interest is important to you and the patient. Detailed function of the structures forming the ventricular systems and the consequences of  injuring them are beyond the scope of this article. The author assumes the reader understands the functional anatomy. What is seen on the monitor depends on the orientation at entry to the ventricle. Structures at the immediate penetration point are difficult to see because they remain behind the lens. Noting the orientation of the patient’s head before draping is critical for the endoscopist’s interpretation of the structures and direction within the ventricular system. Initially, it may be helpful to have the patient’s head straight brow up or lateral to limit the mental gymnastics. As one develops a threedimensional concept of the anatomy, orientation becomes easier. As with all neurosurgical procedures, complications are always a possibility. Only with the use of this information and practice with the scopes

E-mail address:   [email protected]

within the ventricular system will this become a safe and useful procedure.

Development

The cerebral ventricular system at first seems complex; however, when understood from the point of the developmental anatomy, it is much simpler. Telencephalic vesicles bud from the prosencephalon as symmetric bilateral spheres at the extreme rostral end of the embryo. The openings into the diencephalic vesicle, the future third ventricle, become the foramen of Monro. Choroid plexus develops along the dorsal raphae of the diencephalic vesicle and splits at the foramen, extending into each telencephalic vesicle. From this point, the rapidly developing cerebral hemispheres draw a group of structures that originate near the foramen out into the ventricular system. These structures become the endoscopic road maps for the lateral ventricles. Structures that originate near the foramen and end up in the temporal horn include the caudate nucleus, hippocampus, fornix, choroidal fissure, and choroid plexus. In lower mammals, the hippocampal structures move posteriorly along the paramedian with advancing phylogeny to end up in primitive forms near the foramen and, in rodents, over the posterior third ventricle. As the hippocampal structures move posteriorly, the single large bundle of fibers is drawn out and trails behind as the fornix. Columns of the fornix fuse together as they pass over the foramen of Monro. At the anterior commissure, they again separate and each side splits into a precommissural tract and postcommissural tract. These two tracts pass ventrally and laterally, one to the septal area and the other to the mamillary body, thalamus, and midbrain.

1042-3680/04/$ - see front matter    2004 Elsevier Inc. All rights reserved. doi:10.1016/S1042-3680(03)00073-1

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D.G. McLone / Neurosurg Clin N Am 15 (2004) 33–38

In primates, especially man, the parietal lobe has evolved from a structure principally for sensory function of the face to a structure serving intellectual functions. This has caused a large expansion of the parietal lobe driving the temporal lobe with its contents inferiorly and anteriorly. Rapid enlargement of the cortex of the frontal, parietal, and temporal lobes opercularizes the insular cortex. The choroidal fissure with the choroid plexus wraps around the thalamus, passing into the temporal horn along its medial surface. The hippocampus moves with the choroidal fissure into the medial temporal lobe. This process creates a lateral ventricular system that has the form of a ram’s horn. The head of the caudate nucleus begins anteriorly and laterally in the anterior horn of the lateral ventricle. The body and tail of the caudate wrap around the lateral portion of the thalamus, again like a ram’s horn. The venous drainage comes out of the caudate nucleus and thalamus in the groove between the caudate and thalamus, the thalamostriate vein, and ends at the foramen of Monro, where it joins the internal cerebral veins in the roof of the third ventricle. The corpus callosum originates as a commissural bundle anterior to the foramen of Monro and then expands superiorly and posteriorly as the cerebral hemispheres blossom. Obviously, this large midline commissure cannot continue into the temporal lobe because of diencephalic structures occupying the midline. Thus, the caudal end of the corpus callosum, the splenium, comes to rest at the posterior end of the third ventricle above the habenular commissure, the pineal gland, and the Galenic venous system. The columns of the fornix are connected to the corpus callosum by paired thin membranes. As the hippocampus moves posteriorly with the corpus callosum, these membranes are drawn out as the septum pellucidum. This creates two potential cavities. One, located between the leaves of the septum, is the cavum septum pellucidum and its posterior extension, the cavum verge. Below the fornix, the arachnoid and choroidal fissures are folded back over the roof of the third ventricle, creating the second potential space, the cavum vallum interpositum. In children with poorly developed brains, these potential cavities can be large spaces that can either obstruct the ventricular system and cause hydrocephalus or participate with the ventricles in the expansion caused by hydrocephalus. These cavities are also

the sites where missed directed shunts or endoscopes can end up, which presents a confusing picture to the endoscopist. The diencephalic vesicle becomes the third ventricle, and the mesencephalic vesicle, which is the largest portion of the embryonic ventricular system, becomes the relatively small aqueduct. The fourth ventricle is created by the development of the cerebellum from the lip of the rhombencephalon. This lip runs from side to side in the coronal plane. Also developing along the edge of this lip is the choroid plexus of the fourth ventricle. The expansion of the cerebellum rolls the choroid plexus under the caudal edge. Thus, the choroid plexus runs from side to side from one foramen of Luschka to the other in the inferior roof of the fourth ventricle.

Anatomy of the lateral ventricles

In considering the lateral ventricular system, it is helpful to use the designation of the portions of  the ventricle that was employed by neurosurgeons when pneumoencephalography was in common use. Portion 1: the frontal tip of the lateral ventricle to the anterior edge of the foramen of  Monro Portion 2: the anterior edge of the foramen of  Monro to its posterior edge Portion 3: from the posterior edge of the foramen of Monro to the posterior edge of  the thalamus Portion 4: the trigone of the lateral ventricle from the posterior edge of the thalamus to the beginnings of the occipital and temporal horns Portion 5: the occipital horn Portion 6: the temporal horn Portion 1 of the lateral ventricle, with the occipital horn and the tip of the temporal horn, are portions of the ventricle without choroid plexus. The absence of choroid plexus and its immediate proximity to the foramen of Monro are the major identifying characteristics of this portion. Medially is the septum with the septal vein. Inferiorly is the septal area, and laterally is the head of the caudate nucleus. The anterior limit and the roof are formed by the anterior fibers of  the genu of the corpus callosum. These fibers pass obliquely anterior and lateral to the frontal lobe; thus, the anterior horn slopes anterior lateral.

D.G. McLone / Neurosurg Clin N Am 15 (2004) 33–38

Portion 2 of the lateral ventricle is essentially the foramen of Monro and is the structure for orientation within the anterior lateral ventricle. The anterior and superior edge of the foramen is the fornix. Above the fornix is the septum pellucidum, which forms the medial wall of this portion of the ventricle and extends superior to the corpus callosum. The corpus callosum forms the roof, which joins laterally with the head and the beginning of the body of the caudate nucleus. The anterior thalamus forms the floor. The anterior inferior edge of the foramen is the septal area. Turning in the groove between the caudate and thalamus is the thalamostriate vein, which enters the foramen of Monro to join the internal cerebral vein. With the thalamostriate vein, the choroids plexus passes into the foramen and forms the posterior boarder. Portion 3 of the lateral ventricle is that portion of the ventricle located above the thalamus. Its main identifying characteristics are that it is the only portion with the choroid plexus on the medial floor and it is immediately behind the foramen of Monro. The presence of the choroid plexus on the medial floor orients the endoscopist when the approach is posterior from the trigone. The body of the caudate and the roof form the lateral wall by the corpus callosum. The thalamostriate vein is usually a prominent vessel running in the groove between the thalamus and caudate. The septum diminishes rapidly posteriorly so that the most caudal part of the medial surface of portion 3 is formed by the choroid plexus, which covers the fornix. When approaching posteriorly, the choroid plexus and the thalamostriate vein are the road map to portions 1 and 2. The anterior thalamus is at the foramen of Monro, and the fornix and choroid plexus are closely applied to the thalamic surface in portion 3. The distance to the contralateral thalamus through the septum pellucidum is short when the contralateral ventricle is not dilated. Septostomy directed posterior to the foramen and at a small contralateral ventricle risks injury to the contralateral thalamus and internal capsule, especially the genu. Portion 4 of the lateral ventricle is the confluence of portions 3, 5, and 6, often referred to as the trigone. It lies behind the thalamus and contains the glomus of the choroid plexus. Medially, the visual radiations pass to occipital pole, whereas ventrally and laterally is the white matter of the occipital and temporal lobes. It is important to be familiar with the characteristics of 

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the entry into portions 3 and 6 from this portion because this determines whether you enter into the frontal or temporal horns. Portion 5 of the lateral ventricle is the occipital pole and the most variable in size of all the ventricular portions. Again, it is one of the portions without a choroid plexus. Medially and inferiorly are the visual radiations passing to the medial occipital lobe. Superiorly and laterally are the fibers from the splenium of the corpus callosum passing to the lateral and inferior occipital lobe. Portion 6, the final portion of the lateral ventricular system, is located within the temporal lobe. When approaching the trigone posteriorly, the temporal horn is slightly more lateral than portion 3 and the choroid plexus is on the medial roof rather than on the floor. Medially and superiorly are the choroid plexus and hippocampal structures. The deep white matter tracts of the temporal lobe form the lateral wall. Malformations of the lateral ventricles

Many of the malformations of the cerebral hemispheres are associated with hydrocephalus, and ventriculostomy may be a treatment option. Hydrocephalus is a sign that the malformation has created an underlying obstruction causing problems with the circulation of cerebrospinal fluid. As in all good medical practice, a through review of the patient’s history and physical examination and study of the neuroimages before the procedure are essential. Holoprosencephaly results from a lack of division of the prosencephalon into the two telencephalic vesicles. Hydrocephalus with an expanding large dorsal cyst may be present, requiring management of the hydrocephalus. Abnormalities of  the face, such as extreme hypotelorism, reveal the underlying brain malformation. Children with this malformation lack intellectual development. Holoprosencephaly is common with trisomy. Schizencephaly is a defect in the cerebral mantle. It is most common in the third and fourth portions of the ventricular system but can occur in the other portions. The ventricular system may communicate directly with the subarachnoid space, which is referred to as open-lipped schizencephaly. In closed-lip schizencephaly, the lips of the cortical defect are fused. This may be an incidental finding in normal children or associated with seizures or intellectual delay. Hydrocephalus is occasionally present.

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Hydranencephaly is an extreme form of  schizencephaly in which most of the cerebral hemispheres are absent bilaterally, precluding intellectual development. Hydrocephalus is often present. It is essential to distinguish this entity from maximal hydrocephalus, because the outlook is quite different. Porencephaly is a cavity within the paraventricular white matter. Most communicate with the ventricular system. They may be congenital or occur secondary to injury, either vascular or traumatic. Premature infants with intraventricular hemorrhage often have such a cavity located in the frontal lobe, but it may be located anywhere along the germinal matrix. Poorly controlled hydrocephalus can cause a porencephalic cyst to develop along the shunt tract. Diverticula of the ventricular system are rare, but it is essential that they be recognized for what they are. Most often, they occur in cases of  hydrocephalus in which the supra- and infratentorial compartments are isolated from each other. Differential pressures allow a portion of the medial lateral ventricle to herniate into the parasellar or quadrigeminal cisterns. These ‘‘tics’’ usually arise along the choroidal fissure from portions 3 and 4. Agenesis of the corpus callosum results in a major decrease in the amount of white matter in each cerebral hemisphere. Because the third ventricle is not constrained by the corpus callosum, the fornix moves laterally, causing the frontal tips of the lateral ventricles to diverge. Portions 3, 4, and 5 are usually large, so-called ‘‘copocephaly,’’ expanding to fill the space left by the absent white matter. Only rarely is agenesis of the corpus callosum accompanied by hydrocephalus. Ependymal and choroidal cysts are not uncommon within the lateral ventricles. They are usually small and can spontaneously disappear. Occasionally, they are large and obstruct the ventricular pathway, causing hydrocephalus proximal to the obstruction. These cysts can be managed by endoscopic fenestration. Loculations of the ventricular system are rare. What is common is for paraventricular cysts to coalesce and expand, producing what seems to be a loculated portion of the ventricle. When entering these cavities, the absence of ventricular elements, choroid plexus for intense, reveals their nature. Biopsy of the wall reveals it tobe composed ofwhite matter containing myelinated axons. Hydrocephalus is almost invariably present. The hydrocephalus

has usually been complicated by ventriculitis or ventricular hemorrhage. Anatomy of the third ventricle

A clear understanding of the structures that comprise the limits of this ventricle is extremely important to the neuroendoscopist. Even more importantly, the structures just beyond the walls of this ventricle must be clearly understood. Anteriorly, the two fornices come close together in the midline with only a small groove between them, forming the anterior and superior margin of the third ventricle and of the foramen of Monro. As the columns pass ventrally, each splits into an anterior and posterior limb over the anterior commissure and moves laterally, with the anterior limb ending in the septal area and the posterior limb ending in the mamillary bodies. Ventral to the anterior commissure is the lamina terminalis, which ends in the optic chiasm. The superior optic chiasm actually forms a portion of the anterior third ventricle. The roof of the third ventricle is composed of  the choroid plexus, internal cerebral veins, and columns of the fornix. As the most caudal portion of the fornix, the columns move laterally, and an interconnecting band of tissue, the fimbria, forms the posterior superior roof of the third ventricle. Below these structures are the choroid plexus, internal cerebral veins, and velum interpositum. The pineal recess and the pineal gland form the posterior limits of the third ventricle superiorly. Below the recess are the posterior commissure and the aqueduct of Sylvius. The paired mamillary bodies and the hypothalamus form the floor of the third ventricle. The floor slopes downward from the mamillary bodies into the infundibulum and pituitary recess. The mamillary bodies are usually prominent structures that are easily seen. The floor of  the ventricle immediately in front of the mamillary bodies is often not transparent, and structures under it cannot be seen. Usually, when hydrocephalus is present, the floor is thinned and the vascular structures are visible. More anteriorly, the floor of the hypothalamus may be slightly pigmented. Below, exterior to the third ventricle is the posterior clinoid, and between the clinoid and the interpeduncular fossa runs the membrane of Liliequist. If one passes through the floor of the third ventricle in the midline anterior to the mamillary bodies and the basilar artery tip, the prepontine cistern is entered. As one

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move more rostrally and passes through the floor of the hypothalamus, the suprasellar cisterns anterior to the membrane of Liliequist are entered. The floor of the third ventricle is the hypothalamus, and injury can lead to endocrinopathies. Moving too far forward may cause the scope to pin the floor against the posterior clinoid. There are three recesses that can increase greatly in size during hydrocephalus. They are the optic, pituitary, and pineal recesses. When distended, the optic recess leaves the anterior commissure as an obvious structure in the anterior third ventricle. The pituitary recess can become large and thinned to the point of being almost transparent, revealing the structures in the parasellar cisterns. The pineal recess expands into and often fills the quadrigeminal cistern. The lateral walls of the third ventricle are formed by the medial surfaces of the thalami. Passing posteriorly along the superior margin of  the medial thalamus is the stria terminalis, which ends in the habenular nucleus and commissure. Because this structure is often obscured by the choroid plexus of the third ventricle, it is usually not visible through the ventriculoscope. The massa intermedia usually occupies the middle portion of the third ventricle. This is a noncommissural structure of variable size connecting the medial portions of the thalami. In the Chiari II malformation, the massa intermedia occupies a major portion of the third ventricle. Some important vascular structures are located external to the third ventricle in the subarachnoid space. Below the posterior floor of the third ventricle in the interpeduncular cistern are the tip of the basilar artery and the two mesencephalic portions of the posterior cerebral arteries. There are also a number of smaller penetrating arteries that branch from these main trunks. Anteriorly,  just above the optic chiasm are the anterior cerebral arteries and the anterior communicating artery. Running up the anterior surface of the lamina terminalis are the paired anterior cerebral arteries. Malformations of the third ventricle

Severe hydrocephalus can significantly alter the appearance of the structures at the foramen of  Monro. Even in these cases, the basic structures of  the road maps are available to locate the area for ventriculostomy. In the Chiari II malformation, the third ventricle is usually remarkably different from normal. A large portion is occupied by the massa

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intermedia, but, more importantly, the floor is quite different. The distance between the mamillary bodies and the pituitary recess is extremely short, and the floor is thickened. This malformation often precludes any attempt at fenestration of  the floor, especially in infants. Agenesis of the corpus callosum allows the third ventricle to expand superiorly between the cerebral hemispheres. The foramina of Monro are displaced laterally. Anatomy of the cerebral aqueduct

The aqueduct is the small portion of the ventricular system that connects the third and fourth ventricles. Superior to the aqueduct is the quadrigeminal plate. Inferiorly is the tegmentum of the midbrain. Nuclei of the third cranial nerve are located bilaterally near the anterior portion of  the aqueduct. Anatomy of the fourth ventricle

The normal fourth ventricle is a difficult target for endoscopy. Its size and orientation do not allow easy access. More importantly, the floor of  this ventricle is the brain stem. The sixth cranial nerve nucleus, the tract of the seventh cranial nerve, and the medial longitudinal fasciculus are located superficially just below this floor. Although the cerebellum tolerates penetration, minor trauma to the floor inflicts significant neurologic deficits. In pathologic conditions in which the fourth ventricle is enlarged, however, access is possible. The floor of the fourth ventricle is diamond shaped. The anterior point begins at the aqueduct, the lateral points hook slightly posterior to form the lateral recesses, and the posterior point ends at the obex. The normal floor is relatively flat with some identifying structures in it. Running in the midline is the median sulcus, and near the midpoint, the stria medullaris runs from the sulcus toward each lateral sulcus. The facial colliculus is located on either side near midline just rostral to the stria medullaris. The walls of the fourth ventricle are formed by the superior and inferior cerebellar peduncles. The fourth ventricle has a pyramid shape, with the apex tilted slightly posterior. The anterior and posterior medullary velum forms the roof. The posterior side of the pyramid is convex because of the cerebellar vermis bulging inward. The vermis also splits the apex into two recesses: the posterior superior

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recesses. The midline apex is the vestigium. The choroid plexus is located on the posterior surface of  the fourth ventricle and runs in the coronal plane from one lateral recess to the other. Foramina that drain the fourth ventricle are located bilaterally in lateral recesses: the foramina of Luschka and, in the midline, the foramen of Magendie. The choroidal fissure runs with the choroid plexus from one lateral recess to the other, separating the inferior cerebellum from the brain stem. Malformations of the fourth ventricle

Dandy Walker cysts represent a group of  anomalies in which a portion of or the entire cerebellar vermis is absent and the fourth ventricle communicates with or becomes a large cyst. When it occurs early in development, the torcula is located high, often near the midparietal region. Hydrocephalus may or may not be present. In its most severe form, it is associated with other brain malformations, such as agenesis of the corpus callosum, and intellectual delay is common in this form. Loculation of the fourth ventricle, or a trapped fourth ventricle, like loculations in the lateral ventricles, is usually a complication of hydrocephalus. Ventriculitis is the most common cause. The Chiari II malformation is a malformation that affects the entire brain. It has a major impact on the contents of the posterior fossa. Because the size of the embryonic posterior fossa is much too

small to contain the rhombencephalic and metencephalic structures that will develop, derivatives of  these embryonic portions of the brain extrude out of the posterior fossa. A portion of the (occasionally the entire) cerebellum and fourth ventricle is displaced into the cervical canal. In other individuals, the deficient tentorium allows a major portion of the cerebellum and fourth ventricle to herniate upward into the middle fossa between the cerebral hemispheres. When the ventricular shunt fails or the fourth ventricle becomes trapped or isolated, the fourth ventricle expands, increasing the pressure on the surrounding hindbrain. This is usually manifested as a dramatic increase in the patient’s symptoms. When the isolated fourth ventricle in the Chiari II malformation expands superiorly, endoscopic access is available from above in a plane parallel to the floor of the fourth ventricle. This affords the opportunity to fenestrate or shunt the fourth ventricle endoscopically without endangering the floor of the fourth ventricle.

Summary

The embryology of the ventricular development of the brain assists in understanding the final relations between structures forming these cavities. An accurate concept of this anatomy allows the endoscopist to maneuver within the ventricular system.

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Selecting patients for endoscopic third ventriculostomy Harold L. Rekate, MD Pediatric Neurosurgery, Barrow Neurological Institute, 2910 North Third Avenue, Phoenix, AZ 85013, USA

At the annual meeting of the American Association of Neurological Surgeons Meeting in 1995, Professor Fred Epstein was called to discuss our paper on the use of endoscopic third ventriculostomy (ETV) as the ultimate treatment for the ‘‘slit ventricle syndrome’’ (SVS) as presented by Dr Jonathan Baskin [1].   Dr Epstein was surprised to learn that we were viewing all previously shunted patients with shunt problems as potential candidates for the procedure and wondered aloud whether patients with normal pressure hydrocephalus (NPH) might not be considered candidates for ETV. The thought process leading to the following presentation regarding who is and who is not a candidate for ETV was largely generated by that discussion. Can we know beforehand who will and who will not benefit from an ETV? What are the absolute contraindications for performing the procedure? What are the relative contraindications? How can we analyze the risk-benefit ratio for ETV in various clinical settings? For the most part, defining the role of ETV in the overall management of hydrocephalus must await large, multicenter, randomized, prospective trials. In the interim, I will attempt to define a rational approach to the problem in partial answer to the posed questions. Anatomy and biophysics of the cerebrospinal fluid as it relates to third ventriculostomy

The credit for defining the basic pathophysiologic mechanisms in hydrocephalus goes to Walter Dandy and his colleagues at Johns Hopkins University for work done between the second and fourth decades of the twentieth century.

E-mail address:   [email protected]

There had been many previous pathologic descriptions of the effects of hydrocephalus on cadaveric material. Dandy and Blackfan [2] studied laboratory animals and patients with hydrocephalus by injecting supravital dyes into the lateral ventricles of the subjects. They then performed lumbar punctures to determine whether the dye could be recovered in the spinal subarachnoid spaces (SSASs) [3]. Based on this information, Dandy and Blackfan classified hydrocephalus into communicating (the dye was recoverable) and obstructive or noncommunicating (the dye was not recoverable). As a result of  these findings, they recommended attempting to create a communication between the third ventricle and the subarachnoid spaces by performing an open craniotomy and initially resecting one of the optic nerves. By applying Dandy’s classification, patients with noncommunicating hydrocephalus would be considered candidates for ETV to create an internal bypass for the treatment of hydrocephalus. Over the years, there has been a tendency to equate noncommunicating hydrocephalus with triventricular hydrocephalus, which could be diagnosed by air studies and, subsequently, by CT and MRI. In 1960, Ransohoff and Epstein  [4] voiced their objection to the Dandy classification. They believed that all hydrocephalus was obstructive and preferred to classify the condition into intraventricular obstructive hydrocephalus and extraventricular obstructive hydrocephalus. The latter would be consistent with Dandy’s communicating hydrocephalus. Based on this discussion, many patients with communicating hydrocephalus are good candidates for ETV. With current imaging technologies, it is usually possible to determine the actual site of the obstruction and to plan treatment to address the specific pathophysiologic mechanisms involved. In

1042-3680/04/$ - see front matter    2004 Elsevier Inc. All rights reserved. doi:10.1016/S1042-3680(03)00074-3

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our laboratory, we have measured the amount of  resistance that can be anticipated at each point of  potential obstruction. Because of the presence of multiple ventricular catheters, we have also attempted to measure intraventricular pressures in various components in human beings.   Fig. 1 is a schematic diagram of the anatomy of the cerebrospinal fluid (CSF) pathways in a patient with aqueductal stenosis as a hydraulic analogue to an electrical circuit. In normal animals, pressure differentials can be measured only at the level of  flow of CSF from the cortical subarachnoid spaces (CSASs) into the superior sagittal sinus (SSS) [5,6]. For CSF to be absorbed at the level of the SSS, intracranial pressure (ICP) must be 5 to 7 mm Hg higher than the pressure in the SSS.   Fig. 2 is a schematic diagram of the physical effect of an ETV. Essentially, the procedure is an internal bypass between the third ventricle and the interpeduncular cistern in the CSASs. Given this paradigm, all patients with obstructions between the third ventricle and the

CSASs are potential candidates for ETV. Not only can ETV treat hydrocephalus caused by aqueductal stenosis, but it is at least of theoretic benefit in obstruction of the outlet foramina of  the fourth ventricle and to blockage of CSF flow at the level of the basal cisterns between the SSASs and the CSASs. Only when CSF flow is obstructed at the level of the arachnoid villi or venous flow from the sagittal sinus is restricted do patients fail to benefit from ETV. These forms of distal obstruction represent absolute contraindications to ETV. With contemporary neuroimaging techniques, it may or may not be possible to determine the actual site of obstruction to the flow of CSF. The more definitive the diagnosis of the site of  obstruction, the better is the physician’s ability to predict the outcome of ETV when used to treat patients with hydrocephalus. Some patients with hydrocephalus may have an obstruction at more than one point along the CSF pathway. In spina bifida, hydrocephalus caused by a Chiari II

Fig. 1. Schematic hydraulics of the cerebrospinal fluid system with aqueductal stenosis. (Courtesy of Barrow Neurological Institute.)

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Fig. 2. Schematic diagram of the effect of performing an endoscopic third ventriculostomy on the circuit diagram of  cerebrospinal fluid flow. (Courtesy of Barrow Neurological Institute.)

malformation is associated with as many as four different sites of potential obstruction to the flow of CSF [7]. Based on patients’ clinical manifestations at shunt failure, all these potential sites of  obstruction actually occur and any patient may have more than one site of obstruction. Patients with hydrocephalus caused by intraventricular or subarachnoid hemorrhage (SAH) for whatever cause (prematurity, trauma, or aneurysmal bleeding) usually have a CSF absorptive difficulty at the level of the basal cisterns (SSASs to CSASs). They could have an obstruction at the level of the arachnoid granulations, however, which would not respond to ETV. Patients who suffer significant infections may develop hydrocephalus. The most common location is also the basal cisterns. Patients with an infection may have an obstruction at the level of the outlet foramina of the fourth ventricle or at the level of  the arachnoid granulations, however.

Absolute contraindications for endoscopic third ventriculostomy

‘‘Communicating hydrocephalus’’: obstruction to the absorption of cerebrospinal fluid  ETV should not be performed if CSF is already flowing unimpeded between the ventricles and the interpeduncular cisterns. It also should not be done if it is technically impossible to manipulate the endoscope within the lateral and third ventricles to a position that allows the floor of the third ventricle to be visualized. These are the only two absolute contraindications for performing the procedure. In the first instance, flow between the ventricles and the CSASs is not impeded. Bypassing the aqueduct of Sylvius, outlet foramina of the fourth ventricle, and the basal cisterns offers no advantage, because the point of obstruction is ‘‘downstream’’ from the internal bypass. As can be seen from a review of  Fig. 2, this condition occurs only if the arachnoid

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granulations are obstructed or the pressure of the SSS is increased markedly. As an isolated event, obstruction of the arachnoid granulations is quite rare. Pathologically, congenital absence of these structures is the cause of at least some cases of benign familial megalencephaly or external hydrocephalus. Radiologically, this type of obstruction shows mild to moderate ventriculomegaly and distention of  the CSASs [8–10]. The terminal absorptive mechanisms can be clogged by blood or by inflammatory or tumor cells. This clogging is usually accompanied by thickening and scarring of the arachnoid in the basal cisterns. Although the CSF absorptive failures in acute SAH and meningitis may be related to an obstruction at this level, the hydrocephalus usually results from an obstruction between the SSASs and CSASs, a condition that is amenable to ETV. Hydrocephalus caused by obstruction of  absorption to CSF at the level of the arachnoid villi is never an all-or-none phenomenon. It is pressure dependent in that the presence of the particulate matter changes the pressure flow characteristics of the valvular mechanism already present. Under normal conditions, the arachnoid villi (microscopic structures) contained within the arachnoid granulations (macroscopically visible) function as a differential pressure valve between the CSASs and SSS with a closing pressure of 5 to 7 mm Hg (70–100 mm H2O). In adults with closed sutures and fontanels, clogging of the arachnoid villi usually increases ICP, with a minimal increase in ventricular size. In the context of  traumatic or aneurysmal SAH, the usual indication for shunting is the failure to be able to wean the patient from an external ventricular drain in the presence of minimal ventriculomegaly. The shunt can usually be removed later in the course of a patient’s life, but ventricular size may increase significantly with symptoms at the time of shunt failure  [11]. In this case, the point of  obstruction usually is at the level of the basal cisterns and no longer at the level of the arachnoid granulations. In infants with neonatal intraventricular hemorrhage or meningitis, clogging of the arachnoid villi increases both the CSAS and ventricular volume. In this situation, the open fontanels and distensibility of the sutures allow CSF to accumulate, because ICP cannot increase to the point that it will overcome the valvular mechanisms in the arachnoid villi. This condition responds to increasing ICP by wrapping the head with an ace

bandage. ICP then increases to a point where CSF can be absorbed [12]. The second point of obstruction leading to the type of ‘‘communicating hydrocephalus’’ that cannot be affected by ETV involves obstruction to outflow of venous blood from the SSS. In adults, marked increases in pressure in the SSS lead to pseudotumor cerebri rather than to hydrocephalus   [13,14]. In infants with open fontanels and distensible sutures, marked increases in pressure in the SSS lead to marked ventriculomegaly associated with concomitant increases in the volume of the CSASs. At presentation, it may be difficult, if not impossible, to discern that the hydrocephalus is caused by increased venous pressure. This form of hydrocephalus can lead to secondary obstruction of the aqueduct as the brain stem is displaced inward and the temporal horns of  the lateral ventricles displace the midbrain medially [15]. This form of hydrocephalus has been well studied in the context of achondroplasia and craniofacial syndromes   [16–20].   In the case of  Crouzon’s and Pfeiffer’s syndromes, the hydrocephalus may not be evident until a formal cranial remodeling operation has been performed. These patients share the same syndrome in that their ventricles do not dilate to abnormally large volumes at the time of shunt failure. They show signs of overtly increased ICP without ventriculomegaly, a condition that has been referred to as ‘‘normal volume hydrocephalus’’ [21]. Unresponsive ventricles: ventricles too small or too distorted to manipulate an endoscope safely Performing an ETV requires that the endoscope be placed in the lateral ventricle and manipulated through the foramen of Monro to the floor of the third ventricle, where the hole can be made. The smaller the ventricles are, the more difficult it becomes to perform the manipulations needed to fenestrate the floor of the third ventricle. If the size of the ventricles is normal or smaller than normal after chronic shunting, it may be impossible to manipulate the endoscope safely to the appropriate location to perform the fenestration. There are two important circumstances in which third ventriculostomy is contraindicated in this context. Marked enlargement of the massa intermedia of the third ventricle is a well-recognized concomitant of the Chiari II malformation in the context of spina bifida. In these situations, the walls of the third ventricle are often closely opposed because of  the size of the massa intermedia despite the

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Fig. 3. MRI of a patient with spina bifida showing enlargement of the massa intermedia and a small third ventricle despite marked enlargement of the lateral ventricles. ( A) Sagittal T2-weighted MRI demonstrating the enlarged massa intermedia in a small third ventricle despite massive enlargement of the lateral ventricles. ( B) Axial T2-weighted MRI demonstrating the difference in size between the lateral and third ventricles.

enlargement of the lateral ventricles (Fig. 3). The third ventricle can be markedly distorted in patients with a Chiari II malformation. Even when the third ventricle can be cannulated, the anatomic landmarks can be so distorted that it may be impossible to find a point on the floor of the third ventricle to make the fenestration. The second context in which ETV is contraindicated because it would be unsafe to manipulate the endoscope occurs in patients with normal volume hydrocephalus as described previously. These patients have smaller than normal ventricles, and the ventricles do not expand at the time of  shunt failure. These patients should not undergo ETV for two reasons. First, the procedure is associated with a high risk of damaging the columns of the fornix, mamillary bodies, cerebral peduncles, or hypothalamus. Second, ETV in this context is unlikely to be of benefit to the patient. We have performed iohexol ventriculography in 31 such patients, and 28 showed free communication from the ventricle to the interpeduncular cistern [22].   In the 3 patients who did not show such communication, treatment of their hydrocephalus was complicated by a significant infectious process after the original shunt had been placed.

Some nonresponsive ventricles have resulted in surprising observations. In one patient whose hydrocephalus was associated with a pineal tumor originally treated in infancy, overt shunt failure occurred despite no change in ventricular volume. Ventriculography revealed that the dye injected through the shunt into the lateral ventricle rapidly flowed intothe interpeduncular cistern area (Fig.4). The hydrocephalus of patients with normal volume hydrocephalus is related to increased venous pressures, and they are not candidates for ETV for both reasons.

Selection of candidates for endoscopic third ventriculostomy as an initial procedure in the treatment of hydrocephalus

Late occlusion of the aqueduct of Sylvius Hydrocephalus caused by occlusion of the aqueduct of Sylvius is most common in infants who manifest overt hydrocephalus as newborns or whose head circumference rapidly increases after birth. This indication would seem to be ideal for performing an ETV, because occlusion of the aqueduct obstructs CSF flow between the third

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Fig. 4. (A) Sagittal MRI of a child with hydrocephalus associated with a pineal region tumor showing communication between the lateral ventricles and spinal subarachnoid spaces despite the presence of the tumor. ( B) CT of the basal cisterns after iohexol has been injected into the lateral ventricle showing the flow of contrast into the basal cisterns, thus confirming communication in the cerebrospinal fluid pathways.

and fourth ventricles. Theoretically, CSF should be left in the interpeduncular cistern in communication with the arachnoid granulations, which should be normal. Creating this internal bypass between the third ventricle and the cistern should normalize CSF dynamics. Aqueductal stenosis is often diagnosed by MRI only when triventricular hydrocephalus is present and the size of the fourth ventricle is normal. Triventricular hydrocephalus does not always mean that the underlying cause of the hydrocephalus is aqueductal stenosis. The phenomenon of communicating hydrocephalus causing dilatation of the temporal horns of the lateral ventricle and compression of the midbrain from both sides leading to a secondary occlusion of the aqueduct of Sylvius has been discussed previously. In these patients, shunting opens the aqueduct of  Sylvius to CSF flow again [15]. Depending on the initial site of obstruction, the patient may or may not be a candidate for ETV. Regardless of the site of obstruction to CSF flow, infants are usually poor candidates for a third ventriculostomy, presumably because the ventricles fail to respond after third ventriculostomy despite the blockage at the aqueduct. In these cases, the ventricles are quite large; unlike shunting, which literally sucks CSF from the brain, ETV normalizes CSF absorption. The

latter process requires intraventricular pressure to increase 5 to 7 mm Hg greater than atmospheric pressure, which may be impossible in babies with open anterior fontanels. Some authors suggest that these infants should not be candidates for ETV because of their poor response rate [23,24]. Other authors quote low rates of shunt independence after ETV but believe that the benefit is great enough and the risks of the procedure are low enough to justify ETV in infants in an attempt to avoid placing a shunt [25]. Aqueductal stenosis is diagnosed in older children and adults in two contexts. It is difficult to establish treatment criteria for and to assess the outcome of treatment in patients who develop symptomatic hydrocephalus later in life and have extremely large heads. Obviously, these patients have had severe ventriculomegaly from infancy. Oi et al   [26]   have termed this condition   longstanding overt ventriculomegaly of the adult (LOVA). These patients usually have no overt symptoms after undergoing an imaging study for a seizure or minor head injury. Frequently, they have no symptoms related to their hydrocephalus. When asked, some patients identify daily headaches, clumsiness, or poor memory that may or may not have changed recently. How to treat these patients and, indeed, whether to treat these patients are controversial

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issues. Some authors strongly believe that these patients will benefit from intervention, usually ventricular shunting  [27]. Data showing improvement in these patients are hard to find, and such patients seldom have high ICP. My approach to these patients is to obtain formal neuropsychologic studies to determine whether they exhibit problems with higher cognitive function. If so, it is important to determine whether the deterioration is recent or long standing. I then provide patients with the pertinent information and attempt to help them reach a treatment decision. A significant decrease in the size of the lateral ventricles after shunting or ETV is unusual. Shunts can be shown to be working manometrically, but it may be difficult to determine whether an ETV has produced the best outcome. Imaging studies, at least cine MRI through the floor of the third ventricle and preferably the injection of iodinated contrast material into the lateral ventricles to trace its flow into the basal cisterns, is needed to confirm that CSF dynamics have been maximized. There is one important caveat if the decision is made to attempt to treat LOVA with ETV. Occasionally, the head is so large that some neuroendoscopes are too short to reach the floor of the third ventricle. The distance from the skull to the floor of the third ventricle can be measured on the console of the CT or MRI scanner. A selection of endoscopes should be available to obviate this problem. In the second clinical syndrome, older patients develop hydrocephalus caused by aqueductal stenosis from the presence of severely increased ICP. Patients often seek treatment from an ophthalmologist for some form of ophthalmoplegia, such as bilateral sixth nerve palsies or Parinaud’s syndrome. On examination, the patient is found to have bilateral papilledema. This phenomenon can occur as an isolated event with obstruction caused by fusion of the walls of the aqueduct of Sylvius as occurs in some cases of  neurofibromatosis 1. This overt form of late aqueductal stenosis is more likely to result from small benign tumors (tectal gliomas) of the aqueduct. These are true tumors, but their prognosis in terms of propensity to grow or disseminate is usually good   [28]. A direct attack on these tumors, even for a biopsy, is seldom warranted. This acute adult form of hydrocephalus from aqueductal stenosis is perhaps the most compelling and most satisfying condition to treat with ETV. The success rate for this particular subset of  patients is 75% to 80%. The rate of significant

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morbidity, including endocrinopathy, memory deficits, and hemiparesis, has been reported to be 3%. After 1 year, less than 1% are still troubled by complications of ETV   [24].   In this situation, the risk-benefit ratio favors ETV over internal shunting. Hydrocephalus associated with newly diagnosed  brain tumors, particularly of the posterior fossa This area of study is evolving, and the use of  ETV before tumor removal is discussed more than it is reported in the literature. Posterior fossa tumors usually manifest with hydrocephalus and acutely increased ICP. The blockage of the CSF flow meets the criteria for ETV in that CSF flow between the third ventricle and interpeduncular cistern is obstructed. Conceptually, performing an ETV in this context is similar to placing an internal shunt before tumor resection. It relieves symptoms in most patients and thus allows a direct attack on the tumor at a later stage. It shares with the placement of an internalized shunt the possibility, or even the probability, that it will not be needed after the tumor has been removed. It shares with shunts the real possibility of leading to an upward herniation syndrome—the herniation of the superior cerebellar vermis through the tentorium, leading to compression of the midbrain. Typically, contemporary pediatric neurosurgeons begin patients on high doses of  dexamethasone at the time of diagnosis to stabilize their condition. When the tumor is attacked directly, an external ventricular drain is placed before the lesion is removed. The role of ETV in the overall management of  children with brain tumors affecting the CSF pathways is evolving. Soon a series of publications will support its more or less routine use. We await the results of those studies before applying this technique generally. If neurosurgeons elect to perform an ETV before removing a posterior fossa brain tumor, they must carefully review the anatomy as it appears on sagittal MRI scans. In this situation, the brain stem is often pushed anteriorly against the clivus. The distance between the clivus and basilar artery is short, which makes the procedure more risky than it would be otherwise. The procedure should be performed by an experienced neuroendoscopist and can be made significantly safer by using frameless stereotaxy. If tumor resection is not essential to the patient’s outcome, the neuroendoscope becomes

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a much more exciting tool. Adolescent male patients with a pineal tumor that enhances diffusely, hydrocephalus, and no markers of  malignancy (elevated levels of  a-fetal protein or human chorionic gonadotrophin) are likely to have a pineal germinoma. Ideally, these patients should be managed by using an endoscope to perform a third ventriculostomy to obtain a biopsy of the tumor. Definitive treatment can then be managed using conformal radiation therapy. This approach is associated with minimal rates of  morbidity and high rates of success. Hydrocephalus associated with intraventricular and subarachnoid hemorrhage Whether SAH results from diffuse craniocerebral trauma or from the rupture of an aneurysm or arteriovenous malformation (AVM), patients are often left with a significant CSF absorption problem. Treatment is usually improved substantially by the widespread use of external ventricular drains. In these contexts, the most common indication for shunting is failure to wean the patient from the ventriculostomy without high levels of ICP. The ventricles do not dilate. ETV is contraindicated based on the two reasons stated previously. The ventricles are small enough to make performing ETV problematic. The presumed point of obstruction is probably the arachnoidal granulations distal to the interpeduncular cisterns. Therefore, these patients are unlikely to benefit from the procedure. They respond to treatment using either ventricular shunting or lumbar shunting. If it is possible to temporize long enough, they may not need a shunt at all. If the inflammatory process associated with SAH is allowed to continue long enough, the primary point of obstruction becomes the basal cisterns. CSF flow is then occluded between the SSASs and CSASs. This process also follows bacterial or fungal meningitis. Under the Dandy classification system, these forms of hydrocephalus would be considered ‘‘communicating hydrocephalus.’’ Consequently, patients would be considered candidates for ventricular shunting or lumboperitoneal shunting. The obstruction to flow is upstream from the interpeduncular cistern, however, and patients may indeed respond to ETV. In fact, the success of the procedure has been highest in this group. This point of obstruction causes most cases of  NPH [29]. In a small series, three of four patients with NPH had excellent outcomes after treatment

[30]. This approach represents an exciting area for future research. Special case: hydrocephalus in infancy ETV is much less likely to be successful when used to treat infants than when used to treat hydrocephalus later in life. Consequently, a number of authors have concluded that an age less than 6 or 12 months should be considered a contraindication to the use of ETV in the management of hydrocephalus. A number of  reasons may underlie this failure. The first relates to the ability to define the point of obstruction in these babies with severe hydrocephalus. Because of the presence of open fontanels and unfused sutures, the degree of hydrocephalus is greater than when hydrocephalus occurs later in life. Furthermore, it is difficult to interpret the scans to determine the actual point of obstruction. The same patient also may have multiple points of  obstruction, especially when hydrocephalus is associated with the Chiari II malformation (spina bifida cystica). In the latter case, there are four different points of obstruction, and more than one site can be obstructed at once [7].  When hydrocephalus occurs later in life, obstruction is less likely to occur at more than one site. It is also easier to determine where the actual point of  obstruction is based on imaging studies. The second reason relates to the actual physics of the system. When the anterior fontanel is opened widely and the sutures are splayed, the intracranial compartment is essentially in communication with and has the same pressure as atmospheric pressure. Natural absorption of CSF depends on ICP being at least 5 mm Hg greater than sagittal sinus pressure   [5,31,32]. It is often easier for the size of the head to expand than to maintain ICP greater than 5 mm Hg. In addition, Laplace’s law implies that the larger ventricles are, the less distending force is needed to maintain them at that size. Although ETV is less likely to be successful in these children than in older children, good outcomes are obtained in some babies. The procedure also may be safer to perform in infants than in older children or adults. The floor of the third ventricle is more diaphanous in infants than it is likely to be in older children. The basilar artery can be identified with certainty and thus protected. The ventricular membrane is so fragile that it can usually be opened with normal irrigation.

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Theoretically, it is better to have communicating than noncommunicating hydrocephalus. When a patient with hydrocephalus related to aqueductal stenosis experiences a shunt failure, no mechanisms are available to compensate for the increased ICP that accompanies failure of the shunt. If the point of obstruction is distal, a significantly longer time is likely to elapse before the situation becomes critical. Endoscopic third ventriculostomy for programmed shunt removal

Chronically shunted patients may suffer from severe and incapacitating headaches caused by SVS. The percentage of patients suffering from this problem is controversial, and some investigators doubt its existence. If the threshold for making this diagnosis includes not only the classic triad of  severe intermittent headaches lasting 10 to 90 minutes, smaller than normal ventricles on imaging

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studies, and a slowly refilling flushing mechanism but the need to discontinue activity or be brought home from school at least two times per month, about 15% of chronically shunted older children and adults suffer from this condition [33]. Based on chronic monitoring of ICP, we have identified four different pathophysiologic mechanisms responsible for SVS: intermittent proximal obstruction, intracranial hypertension with smaller than normal ventricles and a failed shunt (normal volume hydrocephalus), intracranial hypertension with a working shunt (cephalocranial disproportion), and migraine in shunted patients  [34]. Originally, these patients were managed with shunt revision using higher resistance valves and devices that retarded siphoning. Recently, we have offered these patients the opportunity to assess the possibility of becoming shunt independent [1].   These patients are admitted to the hospital for externalization of their shunt, or their shunt is removed and replaced with an external

Fig. 5. Algorithm for managing shunt-related difficulties with a shunt removal protocol. (Courtesy of Barrow Neurological Institute.)

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Box 1.   Contraindications

to endoscopic third ventriculostomy

Absolute contraindications 

1. Third and lateral ventricles too small to allow safe manipulation of the endoscope within the ventricular system 2. Tumor or other mass lesion obstructing the surgeon’s access to the floor of the third ventricle 3. Proven communication between the CSF that is in the third ventricle with CSF within the interpeduncular cistern Relative contraindications 

1. 2. 3. 4. 5.

Multicompartment hydrocephalus Thickened floor of third ventricle Chiari II malformation Age less than 1 year Distortion of third ventricular anatomy

CSF = cerebrospinal fluid.

ventricular drain. Under controlled conditions in the intensive care unit, their shunt is occluded or raised to a higher level and a scan is obtained. About two thirds of these patients become symptomatic with marked ventricular dilatation. These patients undergo ETV, and 70% tolerate shunt removal. Patients who develop marked intracranial hypertension without ventricular distention undergo cisternographic assessment. In my practice, 28 of 31 patients have been shown to have communicating hydrocephalus and have been treated with lumboperitoneal shunts employing valve systems. In chronically shunted patients, ventricular distention at the time of shunt failure is probably sufficient to recommend ETV (Fig. 5). Summary

ETV using contemporary instrumentation has been used for more than 50 years, but its use has become widespread only in the last 10 to 15 years. Randomized prospective trials comparing ETV with shunts are needed before definitive statements can be made about the role of the former in managing the many forms of hydrocephalus. The absolute and relative contraindications for the use of ETV in the management of hydrocephalus are shown in the  Box 1 on this page. It is important not to presume that a specific radiographic or clinical feature would prevent a patient from responding to this rather new procedure without testing the hypothesis. Patients should be given as much information as possible regarding the risks

and benefits of ETV so they can participate in the decision-making process. When should the role of ETV in the management of hydrocephalus be discussed with a patient? At the initial diagnosis of hydrocephalus, the patient or family should be informed of this potential alternative to shunting for the management of hydrocephalus. I also believe that patients with working shunts who are being followed chronically should be informed about ETV as a potential treatment option when their shunt fails. Every shunt failure or infection should be viewed as an opportunity to explore the possibility that the patient could become shunt independent.

References [1] Baskin JJ, Manwaring KH, Rekate HL. Ventricular shunt removal: the ultimate treatment of the slit ventricle syndrome. J Neurosurg 1998;88:478–84. [2] Dandy W, Blackfan K. An experimental and clinical study of internal hydrocephalus. JAMA 1913;61:2216–7. [3] Dandy W, Blackfan K. Internal hydrocephalus. An experimental, clinical and pathological study. Am J Dis Child 1914;8:406–82. [4] Ransohoff J, Epstein F. Proceedings: avoidance of  shunt dependency. J Neurol Neurosurg Psychiatry 1975;38:410–1. [5] Olivero WC, Rekate HL, Chizeck HJ, et al. Relationship between intracranial and sagittal sinus pressure in normal and hydrocephalic dogs. Pediatr Neurosci 1988;14:196–201.

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[6] Rekate HL. Circuit diagram of the circulation of  cerebrospinal fluid. 1989. Pediatr Neurosurg 1994; 21:248–52. [7] Rekate H. Neurosurgical management of the newborn with spina bifida. In: Rekate H, editor. Comprehensive management of spina bifida. Boca Raton, FL: CRC Publishers; 1991. p. 1–26. [8] Gilles F, Davidson R. Communicating hydrocephalus with deficient dysplastic parasagittal arachnoidal granulations. J Neurosurg 1971;35:421–6. [9] Barlow CF. CSF dynamics in hydrocephalus—with special attention to external hydrocephalus. Brain Dev 1984;6:119–27. [10] Akaboshi I, Ikeda T, Yoshioka S. Benign external hydrocephalus in a boy with autosomal dominant microcephaly. Clin Genet 1996;49:160–2. [11] Rekate H, Nulsen FE, Mack H, et al. Establishing the diagnosis of shunt independence. Monogr Neural Sci 1982;8:223–6. [12] Epstein F, Hochwald GM, Ransohoff J. Neonatal hydrocephalus treated by compressive head wrapping. Lancet 1973;1:634–6. [13] Karahalios DG, Rekate HL, Khayata MH, et al. Elevated intracranial venous pressure as a universal mechanism in pseudotumor cerebri of varying etiologies. Neurology 1996;46:198–202. [14] Pare LS, Batzdorf U. Syringomyelia persistence after Chiari decompression as a result of pseudomeningocele formation: Implications for syrinx pathogenesis: report of three cases. Neurosurgery 1998;43:945–8. [15] Nugent G, Al-Mefty O, Chou S. Communicating hydrocephalus as a cause of aqueductal stenosis. J Neurosurg 1979;51:812–8. [16] Francis PM, Beals S, Rekate HL, et al. Chronic tonsillar herniation and Crouzon’s syndrome. Pediatr Neurosurg 1992;18:202–6. [17] Saint-Rose C, LaCombe J, Pierre-Kahn T, et al. Intracranial venous sinus hypertension: cause or consequence of hydrocephalus in infants? J Neurosurg 1984;60:727–31. [18] Pierre-Kahn A, Hirsch JF, Renier D, et al. Hydrocephalus and achondroplasia. A study of 25 observations. Childs Brain 1980;7:205–19. [19] Cinalli G, Renier D, Sebag G, et al. Chronic tonsillar herniation in Crouzon’s and Apert’s syndromes: the role of premature synostosis of the lambdoid suture. J Neurosurg 1995;83:575–82. [20] Nishihara T, Hara T, Suzuki I, et al. Third ventriculostomy for symptomatic syringomyelia

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using flexible endoscope: case report. Minim Invasive Neurosurg 1996;39:130–2. Engel M, Carmel P, Chutorian A. Increased intraventricular pressure without ventriculomegaly in children with shunts: ‘‘normal volume’’ hydrocephalus. Neurosurgery 1979;5:549–52. Rekate HL, Wallace D. Lumboperitoneal shunts in children. Pediatr Neurosurg 2003;38:41–6. Jones RF, Kwok BC, Stening WA, et al. Neuroendoscopic third ventriculostomy. A practical alternative to extracranial shunts in non-communicating hydrocephalus. Acta Neurochir Suppl (Wien) 1994;61:79–83. Teo C, Jones R. Management of hydrocephalus by endoscopic third ventriculostomy in patients with myelomeningocele. Pediatr Neurosurg 1996;25: 57–63. Buxton N, Macarthur D, Mallucci C, et al. Neuroendoscopic third ventriculostomy in patients less than 1 year old. Pediatr Neurosurg 1998;29:73–6. Oi S, Shimoda M, Shibata M, et al. Pathophysiology of long-standing overt ventriculomegaly in adults. J Neurosurg 2000;92:933–40. Larsson A, Stephensen H, Wikkelso C. Adult patients with ‘‘asymptomatic’’ and ‘‘compensated’’ hydrocephalus benefit from surgery. Acta Neurol Scand 1999;99:81–90. Pollack IF, Pang D, Albright AL. The long-term outcome in children with late-onset aqueductal stenosis resulting from benign intrinsic tectal tumors. J Neurosurg 1994;80:681–8. Di Rocco C, Di Trapani G, Maira G, et al. Anatomo-clinical correlations in normotensive hydrocephalus. Reports on three cases. J Neurol Sci 1977;33:437–52. Mitchell P, Mathew B. Third ventriculostomy in normal pressure hydrocephalus. Br J Neurosurg 1999;13:382–5. Ransohoff J, Shulman K, Fishman R. Hydrocephalus: a review of etiology and treatment. J Pediatr 1960;56:399–411. Cutler R, Page L, Galicich J. Formation and absorption of cerebrospinal fluid in man. Brain 1968;91:707–20. Hyde-Rowan MD, Rekate HL, Nulsen FE. Reexpansion of previously collapsed ventricles: the slit ventricle syndrome. J Neurosurg 1982;56:536–9. Rekate HL. Classification of slit-ventricle syndromes using intracranial pressure monitoring. Pediatr Neurosurg 1993;19:15–20.

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Techniques of endoscopic third ventriculostomy Douglas Brockmeyer, MD Primary Children’s Medical Center, 100 North Medical Drive, Suite 2400, Salt Lake City, UT 84113–1100, USA

Modern techniques of endoscopic third ventriculostomy (ETV) are based on the concept of  establishing a natural conduit for cerebral spinal fluid (CSF) flow through the floor of the third ventricle. Through the years, a wide variety of  techniques have been used as a means to this end and have included both open and closed approaches. The relatively recent application of  endoscopic technology to intraventricular surgery has allowed neurosurgeons to perform third ventriculostomies in a minimally invasive fashion, however. Advances in third ventriculostomy technique have been based on a detailed understanding of third ventricular anatomy, surgical trajectories, and improved instrumentation. The goal of this article is to discuss these issues in detail and to point out the relevant risks and known complications associated with them.

open and closed   [5–12]. Notable among these series is the Toronto experience as reported by Hoffman et al [13], which describes a percutaneous third ventriculostomy technique in the management of noncommunicating hydrocephalus. Significant experience with closed stereotactic techniques was reported by Kelly in 1991   [14]. During this period, neurosurgeons began taking advantage of smaller and smaller endoscopes; eventually, the routine use of fiberoptic or rodlens ETV was accepted. Multiple studies were published in the 1990s reflecting considerable success with endoscopic techniques   [14–27]. The current state of the art in ETV obviously reflects significant new concepts brought out by these pioneering neurosurgeons.

Relevant anatomy History

An understanding of the current state of ETV is not complete without an appreciation of its history. Briefly, in 1922, Walter Dandy originated the concept of third ventriculostomy by performing a craniotomy and fenestrating the lamina terminalis for the treatment of hydrocephalus [1]. This was quickly followed by Mixter [2], who, in 1923, used a urologic endoscope to puncture the floor of the third ventricle, thus ushering in the era of ETV at an early stage. In 1936, Stokey and Scarrf  [3]  and, in 1951, Scarrf  [4]  described their own procedures for third ventriculostomy. In the 1970s and 1980s, a host of authors described various techniques for third ventriculostomy, both

E-mail address:   [email protected]

A brief review regarding the anatomy relevant to ETV is useful. The recognition of critical landmarks and structures is vital to the overall success of ETV. In addition, complications may be avoided when important anatomy is identified early and respected throughout the procedure. Choroid plexus The choroid plexus lies along the floor of the lateral ventricle in the choroidal fissure and is oriented in an anterior/posterior direction. Early recognition of the choroid plexus within the lateral ventricle is a powerful navigational tool because its anterior extent leads to the foramen of  Monro and the third ventricle. Thus, if one’s initial endoscopic trajectory does not lead directly to the foramen of Monro, the choroid plexus can act as a ‘‘road map’’ to lead one to the proper site quickly and efficiently. Even in patients with

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distorted ventricular anatomy, such as those with spina bifida, the choroid plexus remains in the choroidal fissure and still leads to the third ventricle. In patients with large ventricles, this point is not much of an issue, but when the ventricular size is small, early recognition of the choroid plexus is sometimes the only navigational guide a neuroendoscopist has.

this problem are to be aware of the orientation of  your endoscope’s camera in relation to the crosssectional area of the tip and to make appropriate adjustments in the approach trajectory. In addition, if one guides the scope in a handheld fashion, exquisite tactile feedback can be obtained and the surgeon could be alerted to ‘‘hanging up’’ the edge of the endoscope on the fornix.

Fornix The fornix forms the superior and anterior margin of the foramen of Monro. It is important that every effort is made to avoid its injury during endoscopic neurosurgery. Because of its location, however, it can easily be injured during passage of  the endoscope from the lateral ventricle into the third ventricle. The risk of injury is multiplied when multiple passes through the foramen of Monro are made. For that reason, the number of passes of the endoscope through the foramen of Monro should be kept to an absolute minimum. In addition, it is important to recognize that the endoscope’s camera port is only a small percentage of the crosssectional area of the endoscope tip. For that reason, it is easy to assume that if one passes the endoscope easily through the foramen of Monro, the fornix is not injured. This may not be the case, however, because the edge of the endoscope tip near the light source or working chamber may inadvertently cause injury. Potential solutions for

Hypothalamus The paired hypothalami form the lateral walls of the third ventricle. The supraoptic and paraventricular arcuate nuclei are the structures that are at the most risk during third ventriculostomy (Fig. 1). Injury to these structures may have significant endocrinologic consequences. Although some evidence suggests that the supraoptic nucleus is related mainly to vasopressin (antidiuretic hormone) and the paraventricular nucleus to oxytocin, both hormones are found in each nucleus. Therefore, surgical trajectories to the third ventricular floor must be planned with the idea that hypothalamic damage must not occur. Although surgical trajectories are presented in a later section, this concept is important when discussing hypothalamic anatomy. These issues are especially important when spina bifida patients with distorted hypothalamic anatomy undergo ETV.

Fig. 1. Hypothalamic nuclear anatomy adjacent to the third ventricle. Note that the supraoptic and paraventricular nuclei are in close proximity to the third ventricle.

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Third ventricular floor

Lillequist’s membrane

The floor of the third ventricle is essentially a thinned out portion of the hypothalamus and can potentially have functioning hypothalamic nuclei (eg, supraoptic and paraventricular nuclei) within it. As noted previously, this consideration is especially important in patients with spina bifida. The traditional boundaries of the third ventricular floor include the mamillary bodies posteriorly, the walls of the hypothalamus laterally, and the optic chiasm/infundibular recess anteriorly. Within this area is a relative ‘‘safe zone’’ where the third ventricular floor may be entered (Fig. 2). This consists of the area just anterior to the midway point between the mamillary bodies and the infundibular recess. If one penetrates the third ventricular floor posterior to this point, the basilar artery tip or proximal portion of the posterior communicating artery may be encountered. If the floor is penetrated anterior to this point, the clivus is encountered . Obviously, if a choice has to be made, entering slightly more anterior to the midpoint is the safer than entering more posterior to the midpoint. Usually, within the midportion of a thinned-out third ventricular floor, there is a translucent bluish-appearing area that corresponds to a safe zone in which to make the initial opening. How the opening is actually made is discussed in later in this article.

Lillequist’s membrane is an arachnoid plane that contains within it the basilar artery complex and separates the posterior fossa arachnoid cisterns from the suprasellar cisterns. Once a neuroendoscopist penetrates through the floor of the third ventricle, Lillequist’s membrane is frequently encountered and hides the basilar artery complex and prepontine cistern from view. It is important that Lillequist’s membrane be opened to have a successful third ventriculostomy. The goal is to communicate the fluid of the third ventricle to the prepontine cistern area. A clear view of the basilar artery complex, pons, pontine perforators, and clivus must be obtained before an ETV can be considered successful. Failure to recognize this anatomic point may lead to endoscopic failures.

Fig. 2. Line drawing depicting the floor of the third ventricle and the ‘‘endoscopic safe zone,’’ where initial dissection during endoscopic third ventriculostomy should begin.

Endoscopic approaches to the third ventricle

Trajectories For a typical patient with enlarged ventricles undergoing ETV for the first time, a standardized trajectory to the third ventricle should be used. One such trajectory that yields excellent results consists of an entry site at the intersection of the coronal suture and the midpupillary line, with the trajectory of the endoscope slightly medial and oriented in line with the external auditory meatus in an anterior/posterior direction (Fig. 3A). This approach yields an endoscopic trajectory toward the foramen of Monro and into the floor of  the third ventricle. The consistency and excellent results of this approach cannot be overemphasized. A standardized approach is particularly important when previously shunted patients become candidates for ETV. The existing shunt entry site or ventricular catheter trajectory is sometimes positioned so that a safe approach to the third ventricular floor is not feasible. In this situation, a separate burr hole, and sometimes a separate incision, must be made in the standard location, and the standard approach should be employed. It is also possible in this situation to use a flexible endoscope to navigate into the third ventricle. In this author’s experience, however, orientation may be difficult, and the acute curve of the scope may injure brain structures or preclude passing instruments safely down the working chamber. The endoscope trajectory can also be changed based on the preoperative ventricular size. If the

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Type of endoscope to use There are two basic types of neuroendoscopes that are available: rod-lens and fiberoptic. These scopes may be further subdivided into rigid, semirigid, and flexible. Understandably, there is no single endoscope that is adaptable enough to be superior in all applications and situations. Therefore, the neuroendoscopist must be flexible in his or her choice of endoscopes. For instance, if  one encounters an adolescent patient with lateonset aqueductal stenosis and large ventricles, a good argument could be made for being as minimally invasive as possible, and a small, 1-mm, semirigid endoscope could be used for the entire procedure. In that case, the tip of the scope is used to perform the fenestration. The optics of the 1-mm endoscope are sufficient to allow positive identification of critical structures and rapid and safe performance of the third ventriculostomy. A school-aged spina bifida patient with distorted anatomy in the third ventricular floor requires maximum visibility and adaptability, however. This situation requires either a rod-lens system or one of the larger fiberoptic scopes. In either case, anticipating the anatomy of the patient and maximizing visibility must be weighed against potential risks. For the experienced endoscopist, the proper endoscope choice may vary from patient to patient. Techniques of endoscopic third ventriculostomy

Fig. 3. Line diagrams depicting trajectories to third ventricle. (A) Traditional trajectory toward the third ventricle floor beginning at the midpupillary line. (B) Modified trajectory because of the small ventricle size. Note that the entry point is moved slightly medial compared with the standard trajectory.

ventricles are generous, the traditional trajectory described previously may be used. If the ventricles are small, however, the burr hole placement should be slightly medial to the midpupillary line, facilitating an easier approach into a narrow third ventricle (see Fig. 3B).

In discussing techniques of endoscopic third ventriculostomy, it is logical to begin with the simplest technique available and then to proceed toward more complex or sophisticated procedures. The list that is included here is by no means meant to be all-inclusive; however, it is meant to cover most of the more commonly used techniques of ETV and serves primarily as a guide or reference for further reading. Endoscope tip Perhaps the easiest and most straightforward way to perform the fenestration for third ventriculostomy is using the tip of the endoscope itself (Fig. 4). Multiple case series have documented its safety and efficacy over time   [15,19–  21,26,28,29]. In essence, the tip of the endoscope is used as a dissecting tool to penetrate the floor of  the third ventricle and Lillequist’s membrane. Obviously, the smaller the tip of the endoscope, the easier the dissection becomes. This technique’s

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Fig. 4. (A,  B ) Line drawing depicting the use of the endoscope tip to perform the fenestration through the floor of the third ventricle.

critical drawback is that during the moments of  dissection, one’s visualization is completely obscured by the tissue in front of the scope. The lack of visualization is made up for by tactile feedback during manual opening of the third ventricular floor. Sometimes, a ‘‘windshield wiper’’ technique may be used to gently dissect the floor of the third ventricle and Lillequist’s membrane, much like arachnoid dissection in other parts of the brain. With practice, this technique is a safe and effective way of performing a large opening of the floor of  the third ventricle. In addition, the scope tip can be placed into the prepontine cistern to inspect the surrounding anatomy. Obviously, this technique has a rather steep learning curve, and the risk of  basilar artery injury is a very real threat during this procedure. Only endoscopists confident with their dissecting technique using the tip of the endoscope should employ it. A variation of this technique was reported by Wellins et al   [30].   They describe preloading a ventricular catheter over the endoscope. Once the ETV is performed, the ventricular catheter is used to dilate the opening. Dissection/balloon dilatation Perhaps the most widespread and safest technique to open the floor of the third ventricle is to pass some type of semiblunt dissector down the working channel of the endoscope first and then to open a small hole in the floor of the third ventricle (Fig. 5A, B). Next, the dissector is withdrawn, and a 2- or 3-French balloon-tipped catheter (or similar device, such as a wire stone extractor   [30]) is passed through the endoscope and through the initial fenestration in the floor of  the third ventricle (see   Fig. 5C). The balloon is

slowly inflated at the site of the fenestration to enlarge the opening gradually and gently (see Fig. 5D) [15,20,25]. Once the balloon has been opened to its widest diameter, it is deflated and removed and the endoscope is placed through the opening to inspect and confirm that Lillequist’s membrane has been opened (see   Fig. 5E). If not, the procedure is repeated until Lillequist’s membrane is open. Several endoscope manufacturers supply small dissecting tools that are ideal for making the initial opening. The author’s preferred technique is to use the tip of an endoscopic bipolar coagulator. This technique, used either with a rod-lens or fiberoptic endoscope, is safe, simple, and effective. The floor of the third ventricle is under direct visualization during the entire act of fenestration. For these reasons, the dissector/balloon dilatation technique and its variations deserve to be at the top of the list for recommended fenestration techniques. One notable exception is placing a fully inflated balloon-tipped catheter all the way through the third ventricle and pulling it back through the membrane in a fully inflated fashion. It is quite easy to injure the hypothalamic nuclei or to cause significant bleeding with this technique. Saline jet Saline jet irrigation has been used in performing ETV and cyst wall fenestration. The technique involves deploying and then directing a strong jet of saline irrigation in the region of the proposed dissection. The fluid forced from the saline jet atraumatically performs the dissection, at least theoretically. Although this technique has its merits and probably deserves more widespread

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Fig. 5. (A – E ) A series of line drawings depicting the use of an endoscope, blunt dissector, and Fogarty catheter to perform endoscopic third ventriculostomy (see text for details).

use, a saline jet apparatus is not readily available to most operating rooms and would need to be specifically requested. Further work and investigation of this technique are probably warranted before more widespread use is recommended. Saline torch Manwaring   [31]   has previously described the use of the saline torch. As a result of the fact that a potentially dangerous form of active energy is

used during the fenestration, most neuroendoscopic surgeons have moved away from this technique toward blunt dissection of the third ventricular floor. Laser energy The application of laser energy or some other type of active energy source to perform ETV is mentioned here only to discourage its use   [32]. When using a laser or other type of thermal

D. Brockmeyer / Neurosurg Clin N Am 15 (2004) 51–59

energy source to perform the fenestration of the third ventricular floor, absolutely no tactile feedback is available and spread of the energy may easily injure or rupture critical neurovascular structures. Several significant complications, some reported and some unreported, have occurred using this type of technique   [33]. Until safer sources of energy are developed to provide for third ventricular fenestration, these types of  techniques should be avoided. Stereotactic approaches Over the years, several authors have reported closed and endoscopic stereotactic approaches to third ventriculostomy   [11,13,14,19]. One such approach describes guiding a rigid rod-lens scope through the lateral and third ventricle using a predetermined stereotactic trajectory   [19]. Although this type of technique has its merits, it does not allow much room for flexibility, a key factor that may represent a critical margin of  safety in ETV. In addition, because of the extra expense of the preoperative stereotactic scan, extra operative time for stereotactic registration, and extra expense for the stereotactic apparatus, using a stereotactic technique is most likely not a cost-effective way to perform this procedure. Further cost-benefit analysis of this procedure would be important. Doppler ultrasound  In 1998, Schmidt   [34]   described the use of  a micro-Doppler technique to identify the basilar apex before performing the fenestration in the third ventricular floor. In his report, two third ventricular floors were mapped out before fenestration with a high degree of accuracy of  predicting the position of the basilar artery. Although perhaps not necessary in all cases, this type of technique may be extremely useful in performing third ventriculostomies in patients with thick opaque floors or in those patients with distorted anatomy (eg, spina bifida).

Complications

Vascular The most important vascular complication to avoid during ETV is injury to the basilar artery and its nearby branches. Two reports have documented injury to the basilar artery or the

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posterior cerebral artery by the tip of the neuroendoscope or a laser   [33,35]. In one case, a pseudoaneurysm developed at the site of arterial injury, which later required further surgery and trapping   [35]. Obviously, a careful look at the preoperative MRI to identify the position of the basilar artery in the prepontine cistern is extremely helpful in potentially avoiding vascular injury. In addition, placing the initial third ventricular floor fenestration in the safe zone also may prevent an arterial catastrophe. If major arterial injury does occur, several techniques may help in avoiding disaster. One is the preplacement of a Sheath dilator in the lateral ventricle, through which the endoscope is passed. If arterial injury does occur, expression of blood through the Sheath dilator may help to decompress the intracranial compartment during the episode of rapid bleeding before arterial spasm. In addition, the ventricular cavity should be irrigated copiously with saline irrigation for perhaps as long as 20 or 30 minutes. Placement of an external ventricular drain and performance of a postoperative CT scan are mandatory. It is important to remember that although major arterial injuries may occur, most can be avoided by careful planning and meticulous technique. This type of major arterial bleeding should be distinguished from the small amount of bleeding that frequently occurs from the floor of the third ventricle once the fenestration is performed. This bleeding is typically capillary in nature and subsides after 1 to 2 minutes of continuous irrigation. Further bleeding almost always requires only more patience and irrigation. If the CSF is not clear enough to see with an endoscope, the procedure should be abandoned, an external ventricular drain placed, and an emergency head CT scan obtained. Occlusive hydrocephalus The occurrence of acute occlusive hydrocephalus by blockage of the foramen of Monro with the endoscope during continuous irrigation has been described previously  [36]. Recognition and prevention of this potentially lethal complication are important. The size of the endoscope versus the size of the foramen of Monro should be  judged during surgery; if the endoscope plugs the foramen of Monro, the irrigation should be shut off. This problem should be in the endoscopist’s mind if sudden vasomotor instability occurs during ETV.

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Endocrine Because the third ventricular floor is in direct continuity with the hypothalamus, endocrine dysfunction may occur after ETV. In 1996, Teo et al [37] reported four endocrine complications in 55 ETVs. Their complications included diabetes insipidus, increase in appetite, loss of thirst, and amenorrhea. The first two complications resolved completely over time. In a separate report, Teo and Jones   [38]   described transient endocrine complications in 2 of 69 spina bifida patients who underwent ETV. In contrast, reports of other large ETV case series  [15,25]   have reported no endocrine complications. Obviously, any patient who undergoes ETV is at potential risk for damaging critical neuroendocrine structures, such as the supraoptic or paraventricular nuclei. Although it is difficult to prove with the existing data, it makes sense that patients who are at the most risk for endocrine complications during ETV are probably those with spina bifida or a thick third ventricular floor. As expected, the treatment of an endoscope-caused endocrine complication is supportive and hopefully transient. Therefore, careful attention to the regional anatomy as well as willingness to stop a procedure if the anatomy is unfavorable may help to avoid this complication. References [1] Dandy WE. An operative procedure for hydrocephalus. Johns Hopkins Hosp Bull 1922;33:189–90. [2] Mixter WJ. Ventriculoscopy and puncture of the floor of the third ventricle. Boston Med Surg J 1923;188:277–8. [3] Stokey B, Scarrf JE. Occlusion of aqueduct of  Sylvius by neoplastic processes with a rational surgical treatment for relief of resultant obstructive hydrocephalus. Bull Neurol Inst 1936;5:348–77. [4] Scarrf JE. Treatment of obstructive hydrocephalus by puncture of the lamina terminalis and floor of  the third ventricle. J Neurosurg 1951;8:204–13. [5] Avman N, Kanoplat Y. Third ventriculostomy by microtechnique. Acta Neurochir Suppl (Wien) 1979; 28:588–95. [6] Brocklehurst G. Trans-callosal third ventriculochiasmatic cisternostomy: a new approach to hydrocephalus. Surg Neurol 1974;2:109–14. [7] Guiot G. Ventriculocisternostomy for stenosis of  the aqueduct of Sylvius. Puncture of the floor of the third ventricle with a leucotome under television control. Acta Neurochir (Wien) 1973;28:264–89. [8] Jaksche H, Lowe F. Burrhole third ventriculocisternostomy. An unpopular but effective procedure for the treatment of certain forms of occlusive hydrocephalus. Acta Neurochir (Wien) 1986;79:48–51.

[9] Natelson SE. Early third ventriculostomy in myelomeningocele infants—shunt independence? Childs Brain 1981;188:277–8. [10] Reddy K, Fewer HD, West M, Hill NC. Slit ventricle syndromewithaqueductstenosis:thirdventriculostomy as definitive treatment. Neurosurgery 1988;23:756–9. [11] Sayers M, Kosnik E. Percutaneous third ventriculostomy: experience and technique. Childs Brain 1976;2:24–6. [12] Vries J. An endoscopic technique for third ventriculostomy. Surg Neurol 1978;9:165–8. [13] Hoffman HJ, Harwood-Nash D, Gilday DL. Percutaneous third ventriculostomy in the management of non-communicating hydrocephalus. Neurosurgery 1980;7:313–21. [14] Kelly PJ. Stereotactic third ventriculostomy in patients with nontumoral adolescent/adult onset aqueductal stenosis and symptomatic hydrocephalus. J Neurosurg 1991;75:865–73. [15] Brockmeyer DB, Abtin K, Carey L, Walker ML. Endoscopic third ventriculostomy: an outcome analysis. Pediatr Neurosurg 1998;28:236–40. [16] Buxton N, Macarther D, Mallucci C, Punt J, Vloeberghs M. Neuroendoscopic third ventriculostomy in patients less than 1 year old. Pediatr Neurosurg 1998;29:73–6. [17] Dalrymple S, Kelly P. Computer-assisted stereotactic third ventriculostomy in the management of  noncommunicating hydrocephalus. Stereotact Funct Neurosurg 1992;59:105–10. [18] Drake J. Ventriculostomy for treatment of hydrocephalus. Neurosurgery 1993;4:657–66. [19] Goodman RR. Magnetic resonance imagingdirected stereotactic endoscopic third ventriculostomy. Neurosurgery 1993;32(6):1043–7. [20] Goumnerova L, Frim D. Treatment of hydrocephalus with third ventriculocisternostomy: outcome and CSF flow patterns. Pediatr Neurosurg 1997;27: 149–52. [21] Jones RF, Stening WA, Brydon M. Endoscopic third ventriculostomy. Neurosurgery 1990;26:86–91. [22] Kunz U, Goldman A, Bader C, Waldbaur H, Oldenkott P. Endoscopic fenestration of the 3rd ventricular floor in aqueductal stenosis. Minim Invasive Neurosurg 1994;37:42–7. [23] Oka K, Yamamoto M, Ikeda K, Tomonaga M. Flexible endoneurosurgical therapy for aqueductal stenosis. Neurosurgery 1993;33:236–43. [24] Rieger A, Rainov NG, Sanchin L, Schopp G, Burkett W. Ultrasound-guided endoscopic fenestration of the third ventricular floor for non-communicating hydrocephalus. Minim Invasive Neurosurg 1996;39:17–20. [25] Sainte-Rose C, Chumas P. Endoscopic third ventriculostomy. Tech Neurosurg 1996;1:176–84. [26] Teo C, Jones R. Management of hydrocephalus by endoscopic third ventriculostomy in patients with myelomeningocele. Pediatr Neurosurg 1996;25: 57–63.

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[27] Tuli S, Alshail E, Drake J. Third ventriculostomy versus cerebrospinal fluid shunt as a first procedure in pediatric hydrocephalus. Pediatr Neurosurg 1999; 30:11–5. [28] Grant JA, McLone DG. Third ventriculostomy: a review. Surg Neurol 1997;47:210–2. [29] Wellins JCI, Bagley CA, George TM. A simple and safe technique for endoscopic third ventriculocisternostomy. Pediatr Neurosurg 1999;30:219–23. [30] Wong TT, Lee LS. A method of enlarging the opening of the third ventricular floor for flexible endoscopic third ventriculostomy. Childs Nerv Syst 1996;12:396–8. [31] Manwaring K. Endoscopic ventricular fenestration. In: Manwaring K, Crone K, editors. Neuroendoscopy. NewYork: Mary Ann Liebert; 1992. p. 79–90. [32] Wood FA. Endoscopic laser third ventriculostomy. N Engl J Med 1993;329:207–8. [33] McLaughlin MR, Wahlig JB, Kaufmann AM, Albright AL. Traumatic basilar aneurysm after

[34]

[35]

[36]

[37]

[38]

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endoscopic third ventriculostomy: a case report. Neurosurgery 1997;41:1400–3. Schmidt R. Use of microvascular Doppler probe to avoid basilar artery injury during endoscopic third ventriculostomy. Technical note. J Neurosurg 1999; 90:156–7. Abtin K, Thompson BG, Walker ML. Basilar artery perforation as a complication of endoscopic third ventriculostomy. Pediatr Neurosurg 1998;28: 35–41. Handler MH, Abbott R, Lee M. A near-fatal complication of endoscopic third ventriculostomy: case report. Neurosurgery 1994;35:525–7. Teo C, Rahman S, Boop FA, Cherny B. Complications of endoscopic neurosurgery. Childs Nerv Syst 1996;12(5):248–53. Teo C, Jones R. Management of hydrocephalus by endoscopic third ventriculostomy in patients with myelomeningocele. Pediatr Neurosurg 1996;25(2): 57–63.

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Complications of third ventriculostomy Marion L. Walker, MD Primary Children’s Medical Center, 100 North Medical Drive, Salt Lake City, UT 84113, USA

Improvements in instrumentation and growing experience with neuroendoscopy have made it possible to perform endoscopic third ventriculostomy (ETV) safely in a selected group of patients. The complication rate for ETV now approaches the rate for ventriculoscopy in general, approximately 6% to 8%, and is similar to the expected infection rate of shunts   [1,2]. Although the exposure to significant neurologic complications is higher than the risk of a single shunt operation, the possibility of achieving long-term shunt independence with ETV is preferable in good-risk patients when compared with the cumulative morbidity of multiple shunt procedures   [3–6]. The collective morbidity for a ventriculoperitoneal shunt is difficult to quantify; however, a recent prospective multicenter study of children undergoing their initial shunt insertion found that 31% had shunt obstruction, 3% had overdrainage, and 8% had infection within 1 year  [1]. There is a 60% failure rate at 2 years. Many of the complications of ETV are transient in nature. Skilled management of intraoperative problems can keep these complications limited to the intraoperative or perioperative period. At least one author has suggested categorizing complications as ‘‘clinically insignificant’’ and ‘‘clinically significant’’ [2]. Although this system may reflect the long-term outcome of the patient, the most important consideration, it does not emphasize the potentially devastating consequences of seemingly minor intraoperative events. This article seeks to define the most common potential complications of ETV and to identify factors in the pre-, intra-, and postoperative periods that can minimize their occurrence or effects.

Complications of endoscopic third ventriculostomy

Cerebrospinal fluid leak Although rarely reported, cerebrospinal fluid (CSF) leakage can delay wound healing and increase the risk of infection. The possibility of  a CSF leak may be minimized by using the smallest appropriate endoscope (especially in patients with large ventricles) and by minimizing the dural opening. A layered closure of the scalp is necessary. More importantly, however, a CSF leak is frequently a sign of failure of the third ventriculostomy, and close observation for this possibility is required. Pneumocephalus Often considered a minor or insignificant complication, pneumocephalus can delay postoperative recovery and can be associated with headache, nausea, and vomiting. Entrapment of  air at the time of surgery can interfere with direct visualization of the anatomic landmarks that are essential to performing a third ventriculostomy safely. This can be minimized by keeping the patient’s head in a midline anatomic position with the burr hole at or near the most superior point, by carefully flushing all irrigation lines of air bubbles, and by irrigating gently while introducing the endoscope. Attention should be paid to minimizing CSF loss, especially in the early stages of the procedure. Decompression of the ventricular system too rapidly can contribute to the formation of a subdural hematoma. Nitrous oxide should not be used for anesthesia during ETV because of the potential for formation of tension pneumocephalus. Ventriculitis

E-mail address: [email protected]

Fever after ETV is not uncommon. In most cases, it is caused by residual blood in the

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ventricular system. In this setting, fever is selflimited and lasts 24 to 48 hours. In some cases, postoperative fever has been attributed to raising the temperature of the CSF in the third ventricle when employing cautery or laser energy, indirectly heating the hypothalamus. Fever may also herald infection and should be monitored closely with analysis and culture of the CSF   [7,8].  Fukuhara et al [9]  report multiple cases in which preexisting ventricular shunt hardware was found to harbor infection after ETV. We believe that it is important to remove all shunt hardware after ETV whenever possible. Careful and thorough sterilization of the endoscopic equipment and the use of perioperative antibiotics can minimize the occurrence of  infection. Prompt diagnosis and treatment of  ventriculitis are essential. Subdural hematoma Subdural hematoma has been reported after ETV [9]. Significant ventricular dilatation with a thin cortical mantle is a risk factor for subdural hemorrhage. Efforts should be made to avoid rapid drainage of large quantities of CSF, and lost CSF should be replaced with lactated Ringer’s solution. Injury to periventricular structures The floor of the third ventricle is not a membrane but a part of the hypothalamus. It is apparently safe to puncture the floor of the third ventricle but only when it is thinned as a result of  the pressure of hydrocephalus. Amenorrhea, diabetes insipidus, loss of thirst, and increased appetite have been reported after ETV   [2,10,11]. Irrigation solution can also be the cause of  complications. Generous irrigation with normal saline solutions has been associated with disturbance of electrolytes and hypothalamic dysfunction. Late arousal and postoperative confusion have also been noted [2]. These complications are caused by trauma to sensitive hypothalamic structures comprising the walls and floor of the third ventricle. Several strategies can minimize injury to sensitive brain structures in the periventricular region. Careful preoperative evaluation may exclude patients with a narrow third ventricle; some authors have suggested a minimum third ventricular width of 7 to 10 mm  [12,13]. Third ventriculostomy can be performed in small third ventricles, but this increases the risk of injury and should be

attempted only in unusual circumstances and by experienced endoscopists. As experience has grown, the range of patients suitable for third ventriculostomy has widened. A number of  surgeons have performed third ventriculostomy in patients with slit ventricle syndrome, with good results   [14,15]. Modern stereotactic systems and small endoscopes have added a significant margin of safety to the procedure when it is performed in a narrow ventricular system. Positioning of the patient is crucial; we advocate keeping the head in a midline position to simplify the surgeon’s visualization of the anatomic landmarks. In a small space, such as the third ventricle, disorientation can quickly lead to injury of the hypothalamic structures or the fornix. Planning of the incision and placement of the burr hole also play important roles in avoiding parenchymal injury; a narrow third ventricle demands a more medially placed burr hole, with a slightly more vertical trajectory (Fig. 1). Knowledge of the relevant anatomy is crucial because it allows the trajectory of the endoscope to be visualized before surgery and the procedure to be mentally ‘‘rehearsed’’ before making the incision. Once the patient is draped, the surgeon loses access to most of the external landmarks that define the trajectory of the endoscope and reorientation may be difficult. During surgery, emphasis must be placed on controlled efficient movement of the endoscope with constant identification of anatomically relevant structures. When using small endoscopes without a working channel, we place a peel-away

Fig. 1. An artist’s illustration of the proper approach angle for endoscopic third ventriculostomy. The burr hole is made at the coronal suture in the midpupillary line. This provides an appropriate angle of approach through the foramen of Monro to the floor of the third ventricle.

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shea sheath th thro throug ugh h the the fora forame men n of Monr Monro o unde underr direct direct visual visualiza izatio tion; n; this this preven prevents ts injury injury to the struct structure uress surrou surround nding ing the forame foramen n during during remova movall and and rein reinse sert rtio ion n of the the endo endosc scop opee and and allows passage of instruments into the operative area without risk of injury to adjacent structures. Familiari Familiarity ty with the particular particular endoscope endoscope in use is essential. When conditions conspire to make visual visualiza izatio tion n or perfor perforati ation on of the floor floor of the thir third d vent ventri ricl clee diffic difficul ult, t, ther theree shou should ld be a low low threshold for abandoning the procedure. This is considere considered d minimally minimally invasive invasive surgery; surgery; another another attempt can be made at a later time, or a shunt can be placed. Bradycardia/asystole Several authors have reported transient bradycardia or asystole when perforating the floor of  the third ventricle or while enlarging the ventriculostomy  [2,7,9,16]  [2,7,9,16]..  This is presumably caused by a direct mechanical effect on the hypothalamus or as the effect of irrigation. Irrigation fluid can be trapped in the third ventricle if the endoscope fills the the fora forame men n of Monr Monro, o, and and the the addi additi tion on of  a seem seemin ingl gly y insi insign gnifi ifican cantt volu volume me may may caus causee a dram dramat atic ic incr increa ease se in pres pressu sure re.. Hand Handle lerr et al [16] reported [16]  reported a ventricular arrhythmia progressing to asystole while irrigating with the endoscope in the the thir third d vent ventri ricl cle. e. This This wa wass beli believ eved ed to be consis consisten tentt with with expans expansion ion of the third third ventri ventricle cle whil whilee the the endo endosc scop opee prev preven ente ted d egre egress ss of fluid fluid throu through gh the forame foramen n of Monro Monro.. Preven Preventio tion n of  these intraoperative complications lies in limiting the the rate rate of ir irri riga gati tion on,, espe especi cial ally ly in the the thir third d ventricle, and in leaving one port of the endoscope open for the egress of fluid. Managemen Managementt consists consists of ceasing irrigation and withdrawing the endoscope until the patient is hemodynamically stable.

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continued irrigation. Brisk bleeding may also be encountered after injury to intraventricular veins and to perforating arteries and bridging veins in the interp interpedu eduncu ncular lar cister cistern. n. Brisk Brisk bleedi bleeding ng requir quires es si sign gnifi ifica cant nt ir irri riga gati tion on and and may may requ requir iree abando abandonme nment nt of the proced procedure ure.. A pathwa pathway y for CSF to exit is crucial in this circumstance. With Wi thou outt a doub doubt, t, the the most most impo import rtan antt and and potent potential ially ly devast devastati ating ng compli complicat cation ion of ETV is inju injury ry to the the basi basila lar, r, post poster erio iorr cere cerebr bral al,, or posterior posterior communica communicating ting arteries. arteries. After arterial arterial injury, injury, major major hemorrhag hemorrhage, e, vasospasm, vasospasm, pseudopseudoaneurysm, and delayed subarachnoid hemorrhage have have been been report reported, ed, with with signifi significan cantt morbi morbidit dity y and and mort mortal alit ity y (Fi Fig. g. 2)   [17–19]. [17–19]. Alth Althou ough gh the the reported incidence is low, this author is aware of  othe otherr as yet yet unre unrepo port rted ed case cases. s. Beca Becaus usee the the consequences of arterial injury are so profound, it is essential to inform patients and their parents that major arterial injury is a real possibility. Avoidance of hemorrhage is of utmost importance. tance. Carefu Carefull patien patientt evalua evaluatio tion n and select selection ion may exclude patients at high risk or at least alert the surgeon to the specific risk factors. MRI and MR angiography are useful not only to establish the third third ventri ventricul cular ar anatom anatomy y but may demondemonstrate the location of the basilar artery in relation to the floor. During the procedure, the anatomy of  the floor of the third ventricle must be carefully analyzed. The floor may appear opaque, and in

Vascular complications Minor Minor bleeding bleeding that is easily easily controll controlled ed with irrigation is common during ETV. Teo et al [2] reported ‘‘clinically insignificant’’ hemorrhage in 6 of 55 endoscopic ventriculostomies. Of 98 cases, Hopf et al [8] al  [8]  reported venous bleeding in 3 cases, arterial bleeding in 1 case, and 1 case in which there was bleeding from a bridging vein during the openi opening. ng. Fukuh Fukuhara ara et al [9]   reported reported intravenintraventricular tricular hemorrhag hemorrhagee necessitat necessitating ing placement placement of  External Ventricular Drainage in 2 of 89 cases. Small Small vessels vessels may be encountere encountered d within within the floor of the third ventricle. This type of bleeding can can often ften be cont contrrolle olled d with ith patie atien nce and and

Fig. 2. Anterop Anteroposte osterior rior view of a basilar basilar artery angiogram demonstrating a pseudoaneurysm of the posterior communicating artery at the junction with the basilar artery. This aneurysm created by injury to the basilar arter artery y during during endos endosco copic pic third third ventr ventricu iculos lostom tomy y was successfully treated.

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some cases, especially especially in myelomeni myelomeningoce ngocele le patien tients ts,, the the wa wall llss of the the hypo hypoth thal alam amus us may may be partially or entirely fused. If an area of thinning of  the floor can be identified, the procedure can be perfor performed med;; the risk, risk, howev however, er, is increa increased sed with with abnormal abnormal anatomy, anatomy, and under under such conditio conditions, ns, only an experienced endoscopist should attempt the procedure procedure.. A microvascu microvascular lar Doppler Doppler probe probe has been employed successfully in some cases to pinpoint the location of the basilar artery through an opaque floor  [20,21]  [20,21].. The management of most intraoperative hemorrhag orrhagee consis consists ts of irriga irrigatio tion n and patien patience, ce, as previously noted. Electrocautery is rarely helpful and is certainly dangerous in cramped ventricular spaces. In certain instances where the source of  bleeding is in the floor of the third ventricle at the site of fenestration, a balloon catheter can be used to apply hemostatic pressure to the bleeding tissue. In our reported case of basilar artery injury, the patient made a full recovery   [17]. [17]. We believe this was in large part a result of the fact that we had posit position ioned ed the tip of the peel-a peel-away way sheath sheath within within the third third ventri ventricle cle,, allowi allowing ng the arteri arterial al bloo blood d to exit exit the the sheat sheath h inst instea ead d of filli filling ng the the ventricular system. An external ventricular catheter should be placed if any significant intraventricul tricular ar hemorr hemorrhag hagee has occurr occurred. ed. A cerebr cerebral al angiogram should be obtained within 1 to 3 days of any significant hemorrhage to rule out a pseudoaneurysm. Intraoperative bleeding is difficult to quantify as to its significance, and there seem to be differing opinio opinions ns in the litera literatur turee regard regarding ing what what conconstitutes stitutes ‘‘reportab ‘‘reportable’ le’’’ bleeding. bleeding. It is essential essential for the the furt furthe herr refin refinem emen entt of this this tech techni niqu quee that that hemorrhagic complications be reported.

dependent risk factors for ventriculostomy failure andthat nearly nearly half half of ETVfailures ETVfailures occurr occurred ed within within 2 weeks of the procedure, with only 3 of 89 cases failing more than 10 months after ETV  [7]  [7].. It has been suggested that delayed failures are most often a resultof resultof closur closuree of the ventri ventricul culost ostom omy y andcan be managed by repeating the procedure [23] procedure  [23].. Basic principles of complication avoidance

Patient selection As experience has grown and the technique has been been refin refined ed,, thir third d vent ventri ricu culo lost stom omy y has has been been performed successfully and safely in patients with obstructi obstructive ve hydroceph hydrocephalus alus associated associated with aqueductal stenosis, posterior fossa masses, tectal plate tumors, myelomeningocele, and slit ventricle syndrome (Fig. (Fig. 3). 3). Relative contraindications, however, such as postinfectious and posthemorrhagic hydrocephalus, still exist. It is up to the surgeon to match match his or her level of experi experienc ence, e, skill, skill, and confi confide denc ncee with with the the pati patien ent’ t’ss anat anatom omy y and and to inform the patient and family of the risks accordingly. ingly. For For exampl example, e, it may be approp appropria riate te in certai certain n circ circum umst stan ance cess to offer offer ETV ETV to a pati patien entt with with hydroc hydroceph ephalu aluss secon secondar dary y to premat prematuri urity ty and intraventr intraventricula icularr hemorrhag hemorrhage. e. The family family should should be aware aware that that the proced procedure ure has a signifi significan cantly tly

Failure of third ventriculostomy The succes successs of third third ventri ventricul culost ostom omy y lies lies in larg largee part part in sele select ctin ing g pati patien ents ts whos whosee CSF CSF physio physiolog logy y can respo respond nd favora favorably bly to the proprocedure cedure.. Initia Initially lly,, the proced procedure ure was perfor performed med primarily for late-onset aqueductal stenosis, with good results [22] results  [22].. As familiarity with the technique has grown, grown, the indica indicatio tions ns have have broade broadened ned and patients patients with noncomm noncommunic unicating ating hydrocepha hydrocephalus lus result resulting ing from from earlyearly-ons onset et aquedu aqueducta ctall stenos stenosis, is, posterior posterior fossa masses, masses, tectal tectal plate tumors, tumors, and myelomeningocele have been included as well as younger patients [7,23–27] patients  [7,23–27].. A recent review found that a history of shunt infection infection and postopera postoperative tive meningiti meningitiss were in-

Fig. Fig. 3. An endosc endoscopi opicc view view of the floor of the third third ventricle ventricle in a patient patient with myelomeni myelomeningoc ngocele. ele. Almost Almost compl complete ete fusion fusion of the floor of the third ventric ventricle le is present. The mamillary bodies are not identifiable. There is thin thinni ning ng of the the floor floor in two two area areas. s. Succ Succes essf sful ul endoscop endoscopic ic third ventricu ventriculosto lostomy my was accompli accomplished shed through the most posterior area of thinning.

M.L. Walker Walker / Neurosurg Neurosurg Clin N Am 15 (2004) 61–66

less chance of success, however. In these patients, preo preope pera rati tive ve MR MRII shou should ld play play a larg largee role role in dete determ rmin inin ing g the the pati patien ent’ t’ss suit suitab abil ilit ity y for for the the procedure.

65

especially especially in previousl previously y shunted shunted patients patients whose shunts have been removed. With the exception of  infants, we prefer to leave an external ventricular drai drain n in plac placee and and moni monito torr the the pati patien entt in the the intensive care unit after surgery.

Proper training Manipulating the endoscope is a learned skill and one for which there can be a steep learning curve. Familiarity with the endoscope, knowledge of the relevant anatomy, and preoperative visualization of the trajectory are important factors in avoidi avoiding ng compli complicat cation ions. s. We are now now in an era when computer modeling of surgical procedures is possi possible ble,, and this this resour resource ce wil willl play play an increa increassingly important role in training for ETV. Positioning Proper positioning of the patient is crucial to maintain maintain orientatio orientation n during during the procedure procedure.. The head should be in the midline position and slightly elevated. The burr hole should be placed with the final final trajec trajector tory y in mind, mind, and the anatom anatomy y and trajectory should be visualized before the patient is covered by surgical drapes (see Fig. (see  Fig. 1). 1). Endoscopic equipment The The endo endosc scop opee with with the the smal smalle lest st diam diamet eter er appropriate to the patient should be chosen. The method of perforation of the floor is a subject on which there are many differing opinions. The most popular method is to use a pointed (but not sharp) instrument to open the floor and then to expand the opening with a balloon. We firmly believe that laser, cautery, and other forms of energy should not not be employ employed ed becaus becausee they they signifi significan cantly tly increase the risk of arterial injury  [17,18]  [17,18].. Intraoperative management of complications Irri Irriga gati tion on and and pati patien ence ce are are the the two two most most impo import rtan antt meth method odss for for achi achiev evin ing g hemo hemost stas asis is during ETV. The surgeon should also remember that ETV is a minimally invasive procedure and should be abandoned if conditions (eg, bleeding, unfavorable anatomy) conspire to make fenestrating the floor too dangerous. If significant bleeding occurs, an external ventricular drain should be left in place at the close of the procedure. Postoperative management In our our experi experienc ence, e, intrac intracran ranial ial pressu pressure re remain mainss elev elevat ated ed for for 24 to 48 hour hourss afte afterr ETV, ETV,

Summary

As experience with ETV grows, the procedure willl be perfor wil performed med by an increa increasin sing g numb number er of  neurosurgeons. Although the technique has been greatly refined since its advent almost a century ago, today’s neurosurgeon neurosurgeon must never forget that this seemingly simple procedure holds the potential tial for a numbe numberr of devast devastati ating ng compli complicat cation ions. s. Appropri Appropriate ate training training and experience experience are imporimportant tant to the the succ succes esss of ETV ETV and and for for avoi avoidi ding ng comp compli lica cati tion onss It is impe impera rati tive ve that that surg surgeo eons ns cont contin inue ue to repo report rt thei theirr expe experi rien ence ce with with the the complications of ETV so that the procedure can continue to be made as safe as possible.

References [1] Drake Drake J, Kestle Kestle J, Mil Milner ner R, Cinall Cinallii G, Boop F, Piatt Pia tt J, et al. Rando Randomiz mized ed trial trial of cerebr cerebros ospin pinal al fluid shunt valve design in pediatric hydrocephalus. Neurosurgery Neurosurgery 1998;43:294–303. [2] Teo C, Rahman Rahman S, Boop Boop FA, Cherny Cherny B. Compli Compli-cations cations of endoscop endoscopic ic neurosur neurosurgery gery.. Childs Childs Nerv Syst 1996;12:248–53. [3] Guzelbag Guzelbag E, Ersahin Ersahin Y, Mutluer Mutluer S. Cerebros Cerebrospina pinall fluid shunt complications. Turk J Pediatr 1997;39: 363–71. [4] [4] Iskan Iskanda darr B, Tubb Tubbss S, Ma Maps psto tone ne T, Grab Grabb b P, Bartolucci A, Oakes W. Death in shunted hydrocephalic children in the 1990s. Pediatr Neurosurg 1998;28:173–6. [5] Lazareff Lazareff J, Peacock Peacock W, Holly L, Halen JV, Wong A, Olmstead C. Multiple shunt failures: an analysis of relevant factors. Childs Nerv Syst 1998;14:271–5. [6] Lee JY, Wang KC, Cho BK. Functioning Functioning periods periods and complications of 246 cerebrospinal fluid shunting procedures in 208 children. J Korean Med Sci 1995;10:275–80. [7] [7] Broc Brockm kmey eyer er D, Abti Abtin n K, Care Carey y L, Wa Walk lker er M. Endosc Endoscop opic ic third third ventri ventricul culost ostom omy: y: an outco outcome me analysis. Pediatr Neurosurg 1998;28:236–40. [8] [8] Ho Hopf NJ, NJ, Grun Gruneert P, Fri riees G, Resc esch KD, Pernecz Perneczky ky A. Endoscop Endoscopic ic third ventricu ventriculost lostomy: omy: outcome analysis of 100 consecutive procedures [see comments]. Neurosurgery 1999;44:795–806. [9] Fukuhara T, Vorster Vorster S, Luciano M. Risk factors factors for failur failuree of endosc endoscopi opicc third third ventri ventricul culost ostomy omy for obstructive hydrocephalus. Neurosurgery 2000;46: 1100–9.

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[10] Drake JM. Ventriculostomy for treatment of hydrocephalus. Neurosurg Clin North Am 1993;4:657–66. [11] Lowry D, Lowry D, Berga S, Adelson P, Roberts M. Secondary amenorrhea due to hydrocephalus treated with endoscopic ventriculocisternostomy. Case report. J Neurosurg 1996;85:1148–52. [12] Hoffman HJ, Harwood-Nash D, Gilday DL. Percutaneous third ventriculostomy in the management of noncommunicating hydrocephalus. Neurosurgery 1980;7:313–21. [13] Jones R, Stening W, Brydon M. Endoscopic third ventriculostomy. Neurosurgery 1990;26:86–91. [14] Baskin JJ, Manwaring KH, Rekate HL. Ventricular shunt removal: the ultimate treatment of the slit ventricle syndrome. J Neurosurg 1998;88:478–84. [15] Reddy K, Fewer HD, West M, Hill NC. Slit ventricle syndrome with aqueduct stenosis: third ventriculostomy as definitive treatment [see comments]. Neurosurgery 1988;23:756–9. [16] Handler MH, Abbott R, Lee M. A near-fatal complication of endoscopic third ventriculostomy: case report. Neurosurgery 1994;35:525–8. [17] Abtin K, Thompson B, Walker M. Basilar artery perforation as a complication of endoscopic third ventriculostomy. Pediatr Neurosurg 1998;28:35–41. [18] McLaughlin M, Wahlig J, Kaufman A, Albright A. Traumatic basilar aneurysm after endoscopic third ventriculostomy: case report. Neurosurgery 1997; 41:1400–3. [19] Schroeder HW, Warzok RW, Assaf JA, Gaab MR. Fatal subarachnoid hemorrhage after endoscopic third ventriculostomy. Case report. J Neurosurg 1999;90:153–5.

[20] Cartmill M, Vloeberghs M. The use of transendoscopic Doppler ultrasound as a safety-enhancing measure during neuroendoscopic third ventriculostomy. Eur J Pediatr Surg Suppl 1999;1: 50–1. [21] Schmidt R. Use of microvascular Doppler probe to avoid basilar artery injury during endoscopic third ventriculostomy. J Neurosurg 1999;90:156–8. [22] Hirsch J, Hirsch E, Sainte-Rose C, Renier D, Pierre-Kahn A. Stenosis of the aqueduct of Sylvius. Etiology and treatment. J Neurosurg Sci 1986;30: 29–39. [23] Cinalli G, Sainte-Rose C, Chumas P, Zerah M, Brunelle F, Lot G, et al. Failure of third ventriculostomy in the treatment of aqueductal stenosis in children. J Neurosurg 1999;90:448–54. [24] Cinalli G, Salazar C, Mallucci C, Yada JZ, Zerah M, Sainte-Rose C. The role of endoscopic third ventriculostomy in the management of shunt malfunction. Neurosurgery 1998;43:1323–9. [25] Jones R, Kwok B, Stening W, Vonau M. The current status of endoscopic third ventriculostomy in the management of non-communicating hydrocephalus. Minim Invasive Neurosurg 1994;37: 28–36. [26] Jones R, Kwok B, Stening W, Vonau M. Third ventriculostomy for hydrocephalus associated with spinal dysraphism: indications and contraindications. Eur J Pediatr Surg 1996;6:5–6. [27] Teo C, Jones R. Management of hydrocephalus by endoscopic third ventriculostomy in patients with myelomeningocele. Pediatr Neurosurg 1996;25: 57–63.

Neurosurg Clin N Am 15 (2004) 67–75

Results of endoscopic third ventriculostomy Mark R. Iantosca, MDa,*, Walter J. Hader, MD, FRCS(C) b, James M. Drake, FRCS(C) c a

Connecticut Children’s Medical Center, 100 Retreat Avenue, Suite 705, Hartford, CT 06106–2565, USA b Division of Neurosurgery, University of Calgary, Alberta Children’s Hospital, Calgary, Alberta, Canada c Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8 Canada

The recent resurgence of interest in ventriculostomy has arisen out of dissatisfaction with the complications and long-term outcomes of conventional cerebrospinal fluid (CSF) shunting systems  [1,2].   Initial attempts at ventriculostomy via open craniotomy and subsequent percutaneous fluoroscopic and CT-guided techniques have largely been replaced by modern endoscopic procedures with reduced morbidity   [3,4]. Unfortunately, sufficient long-term follow-up data necessary for direct comparison with outcomes of  conventional shunting (CS) procedures are currently unavailable. Clinical decisions regarding use of endoscopic third ventriculostomy (ETV) are based on the results of studies with mean follow-up intervals of less than 5 years. Results of  ETV are most closely associated with the etiology of hydrocephalus encountered as well as with the clinical and radiographic features of the individual patient. Factors affecting outcome

Hydrocephalus etiology Third ventriculostomy is designed to treat noncommunicating hydrocephalus with patent subarachnoid spaces and adequate CSF absorption. It is not surprising, therefore, that the results

of this procedure are most strongly influenced by the etiology of hydrocephalus.   Box 1   depicts hydrocephalus etiologies divided according to reported success rates of ETV. Patients with acquired aqueductal stenosis or tumors obstructing third ventricular outflow have demonstrated the highest success rates, exceeding 75% in carefully selected series of patients   [4–10]. Previously shunted patients with or without myelomeningocele, tumors, or cystic abnormalities leading to fourth ventricular outflow obstruction (ie, arachnoid cyst, Dandy-Walker malformations) and patients with congenital aqueductal stenosis have shown an intermediate response   [6,7,9,11–  13]. Further study of this intermediate group is likely to identify subgroups with higher success rates. Infants developing hydrocephalus after hemorrhage or infection or with associated myelomeningocele (without prior shunting procedure) have demonstrated a poor response to ventriculostomy   [3,5,13–16]; despite limited reports of  success in such patients   [7,11,12,17–20], they are more controversial candidates for this procedure. The procedure is not advisable in patients who have undergone prior radiation therapy because of the extremely poor response rates, altered anatomy (ie, thickened third ventricular floor), and increased risk of bleeding  [3,7,11]. Aqueductal obstruction by stenosis or tumor

* Corresponding author. E-mail address: [email protected] (M.R. Iantosca).

Blockage to CSF flow at the level of the cerebral aqueduct by anatomic or postinflammatory septations/membranes or by extrinsic compression

1042-3680/04/$ - see front matter    2004 Elsevier Inc. All rights reserved. doi:10.1016/S1042-3680(03)00067-6

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Box 1.  Endoscopic

third ventriculostomy success rates by hydrocephalus etiology High success rates (>75%)  Acquired aqueductal stenosis Tumor, cyst, or infectious lesion obstructing third ventricular outflow Tectal, pineal, thalamic, or intraventricular tumor Arachnoid cyst Toxoplasmosis Shunt malfunction in patient with obstructive etiology Intermediate success rates  (approximately 50%)  Tumor obstructing fourth ventricular outflow Myelomeningocele (previously shunted, older patients) Congenital aqueductal stenosis ‘‘Cystic’’ abnormalities obstructing fourth ventricular outflow Arachnoid cysts Dandy-Walker malformation Previously shunted patients with ‘‘difficulties’’ Slit ventricle syndrome Recurrent or intractable shunt infections Recurrent or intractable shunt malfunctions Low success rates ( 6 mm Flexible > 4 mm Thinned floor of third ventricle Downward bulging floor draped over clivus Basilar posterior to mamillary bodies Absence of structural anomalies impeding procedure  Arteriovenous malformation (AVM) or tumor obscuring third ventricular floor Enlarged massa intermedia Insufficient space between mamillary bodies/basilar and clivus Basilar artery ectasia

before this age. Most of the successes in these groups were in previously shunted patients   [21]. Several studies show success rates at or below 50% in patients less than 2   [6,7,9] or 1   [8,15,16] year of age, regardless of etiology. Results are even poorer in patients less than 6 months of age [12,21]. Teo and Jones  [12] demonstrated statistically significant (P = 0.005) lower success rates in patients less than 6 months of age versus older patients (12.5% vs. 80%). Open third ventriculostomy has also been shown to have a dramatically decreased success rate in patients less than 6 months of age [18,22]. The results of these studies are seemingly contradicted by the recent report of  Cinalli et al [4], who demonstrated no difference in failure rates of ETV between patient groups older or younger than 6 months, concluding that patient age should no longer be considered a contraindication to the procedure. Despite the lower success rates and increased morbidity that they report in this younger age group, several authors still advocate an initial attempt at ventriculostomy in these patients so as

to avoid the lifelong complications of shunting [8,15,16]. These authors argue that the ‘‘successes’’ are spared the long-term morbidity, mortality, and economic burden of repeated evaluations and hospitalizations for shunt evaluation. Barlow and Ching   [23]   recently published an analysis of  anticipated cost reduction comparing ETV and CS for treatment of obstructive hydrocephalus at their institution, estimating a reduction of 74 hospital days and nine surgeries annually. This study, however, assumes a success rate of 80%, with no subsequent admissions or procedures for complications or failures among the successful procedures. Insufficient long-term data currently exist to support this argument in younger patient groups, particularly given the often-cited reduced success rates and increased rates of complications. ETV in this younger age group has also been advocated as a primary treatment to remove intraventricular hemorrhage or purulent CSF, assuming that this will result in a more suitable environment for shunt insertion   [15,24,25]. Comparison of this procedure with standard

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‘‘temporizing measures,’’ such as ventriculostomy, ommaya placement, and ventriculosubgaleal shunting is needed to determine comparative efficacy and safety. Interestingly, a recent report by Tisell et al [26] demonstrates an increased failure rate of ETV in older adults with aqueductal stenosis. These delayed failures were hypothetically attributed to decreasing CSF absorptive capacity as a result of  age-related loss of arachnoid villi and decreasing resistance to transependymal CSF resorption over time. Only 50% of ETVs were successful in this series, with almost all failures occurring after an initially favorable response lasting between 1 month and 1 year   [26]. An earlier report by Kelly [5]   demonstrated a 94% success rate in a population of adults with the same etiology treated with stereotactic CT-guided ventriculostomy. Interestingly, most patients in Kelly’s series were previously shunted (11 of 16), whereas only 3 of Tissell et al’s 18 patients had existing shunts. Clearly, further delineation of the pathophysiology of age-related changes in CSF absorption, and development of studies to quantify this capacity, would greatly benefit clinicians attempting to identify appropriate patients for ETV. Previous shunting Multiple studies have demonstrated a trend toward more successful ventriculostomy outcome in patients with existing shunt systems   [6,12,21]. Teo and Jones   [12]   demonstrated a statistically significant difference in success rates for previously shunted patients with myelomeningocele (84%) versus those never shunted (29%; P = 0.002). In fact, third ventriculostomy has been found to be useful in the treatment of  intractable shunt infections and malfunctions and even slit ventricle syndrome refractory to other treatments [5,11,24,27–30]. Other series of ventriculostomy in previously shunted patients have been less promising   [13,31]. These contradictory results may reflect the mix of patients in small series. High success rates in patients with aqueductal obstructive etiologies present a strong argument in favor of ETV for patients in this group who present with shunt malfunction. Improved outcome in previously shunted patients with other etiologies is commonly attributed to increased CSF absorptive capacity; however, the effect of the shunt itself on CSF absorption is difficult to distinguish from the effect of increased age in these patients.

Preoperative assessment of CSF absorptive capacity has been advocated by some authors [32,33], but these techniques have not been widely accepted   [7,21]. Because the patency of CSF pathways is one of the assumptions on which the procedure is based, a preoperative CSF absorption study would be invaluable in identifying patients who would likely benefit from ventriculostomy. The observed delay between operation and decrease in ventricular size (see section on assessing outcome) suggests that CSF absorption may increase slowly after ventriculostomy, however. Therefore, preoperative assessment of CSF absorptive capacity may fail to identify all appropriate patients [7]. Until an accurate functional predictor of this capacity is practical, radiographic assessment of the obstructive pattern of hydrocephalus by MRI is likely to remain the preoperative diagnostic procedure of  choice. Anatomy Preoperative MRI optimally demonstrates all relevant anatomic features and should be obtained for all proposed third ventriculostomy patients. Initially, confirmation of noncommunicating hydrocephalus of favorable etiology should be established by the pattern of ventricular dilatation. Anatomic obstruction of CSF pathways between the aqueduct and the fourth ventricular outflow foramina may be visible on T2- or T1-weighted contrast images. Additionally, T2-weighted and cine images should reveal no evidence of the normally present aqueductal CSF flow pattern. Once the patient’s suitability for the procedure has been established, the neurosurgeon must clarify the details of third ventricular anatomy that are likely to affect morbidity. First, the width of the third ventricle and diameter of the foramen of Monro must be sufficient to accommodate the endoscope of choice. Additionally, the thickness of the third ventricular floor and anatomy of  the proposed puncture site must be assessed in relation to vital structures, particularly the basilar artery and its branches. A downward bulging third ventricular floor draped over the clivus has been cited as a prerequisite for success of this procedure in the past, but others have not found this to be necessary  [3,7]. Ultimately, the surgeon must be satisfied that there is no structural lesion (ie, tumor, AVM) or anatomic variation that would render the procedure unduly difficult or

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hazardous. In cases of doubt, it is reasonable to visualize the floor of the third ventricle and to abandon the procedure if the floor is unsuitable. Reported procedure abort rates as a result of  unfavorable anatomy or intraoperative bleeding range from 0% to 26% (Table 1). Assessing outcome

ETV has yielded a higher success rate with lower morbidity and mortality than earlier methods of third ventriculostomy. Mortality rates for open ventriculostomy procedures varied between 5% and 27%, with success rates from 37% to 75%   [3,5,18,31,34,35].   Percutaneous radiographic and, later, CT-guided techniques reduced this mortality rate to 2% to 7%, with a 44% to 75% rate of shunt independence  [3,5,14,19,31,36]. Most recent studies using modern endoscopic techniques and equipment, with or without stereotactic CT or MRI guidance, have reported low morbidity (3%–12%) and extremely rare mortality, with success rates greater than 75% for carefully selected patient groups.   Table 1 depicts the results of recent ETV studies with success rates by etiology where these data are available. The current challenge is to define appropriate indications and devise objective measures for pre- and postoperative assessment of these patients. The goal of ETV and, to date, the best objectively quantifiable measure of a successful outcome is shunt independence. Vague outcome measures, such as ‘‘successful,’’ ‘‘improved,’’ or ‘‘favorable,’’ are used in a number of studies [12,21]. Only two reports have critically compared modern ETV techniques with CS  [37,38]. SainteRose   [38]   reported no statistically significant differences in measures of neurologic, endocrinologic, social, or behavioral outcomes in a group of  68 patients treated for aqueductal stenosis with either ETV (n = 30) or CS (n = 38). Tuli et al [37] demonstrated no difference in failure rate between ETV (n = 32, 44% failure rate) and CS (n = 210, 45% failure rate) in a prospectively followed group of patients with aqueductal stenosis or tumor. The long-term outcomes of CS, including multiple procedures for obstruction, infection, and overdrainage, have been well documented. Failure rates range from 30% to 47% over 1 year to 63% to 70% over 10 years   [39–42]. Additional long-term studies of ETV and analytic comparison to established CS outcomes are necessary to clarify clinical decisions in these patients.

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One of the most confusing aspects of outcome evaluation in ETV patients is the failure of the ventricles to return to normal size. Many reports detail a gradual decrease in the ventricular size over months to years after surgery, with resolution of periventricular edema and increased extracerebral spaces coinciding with clinical improvement [5–8,31,38]. One series of patients treated with either CSF shunts or ETV showed no difference in intellectual outcome despite enlarged ventricles in the ETV group   [38].   Radiographic evaluation of  suspected closure has been confounded by the presence of persistently enlarged ventricles. Studies detailing the serial measurements of  multiple radiographic indices of ventricular size after surgery show that the third ventricular size responds more quickly (usually within 3 months) than the lateral ventricular size (up to 2 years) [43,44]. Additionally, third ventricular size seems to correlate most closely with outcome in these patients [8,43,44]. A recent study limited to adult patients showed no relation between ventricular size reduction and outcome   [26].   Kulkarni et al [45]   have demonstrated a greater reduction in ventricular size after successful procedures versus treatment failures in 29 children. MRI and Doppler ultrasound studies documenting CSF flow through a patent ventriculostomy are currently the most useful and widely used postoperative radiographic indices. MRI detection of T2-weighted flow void around the ventriculostomy has been correlated with clinical outcome in ETV   [46–48]. This observation has proven most helpful in confirming ventriculostomy patency after surgery, particularly in patients with persistent ventriculomegaly   [47,48]. Kulkarni et al   [45]   have recently demonstrated a statistically significant relation between evidence of postoperative aqueductal CSF flow on MRI and clinical success. Multiple studies have reported long-term patency of third ventriculostomy by means of cine phase contrast (PC) MRI studies. A report by Cinalli et al [4]  included 15 patients with confirmed long-term (>10 years) patency of their ventriculostomy on cine PC MRI (median = 14.3 years, range: 10–17 years). Unfortunately, several recent studies in adults and children have demonstrated a lack of correlation between postoperative MRI findings and outcome [15,16,26,37]. Quantification of flow velocity through ventriculostomies has also been achieved by PC MRI and Doppler ultrasound   [49,50]. Hopefully, methods of quantifying ventriculostomy function will allow neurosurgeons to refine

 7   2   

Table 1 Outcome of endoscopic third ventriculostomy by etiology

Author/Year

Age mean (range)

Morbidity

Jones et al / 1990  [11] Jones et al / 1992 [6] Jones et al / 1994 [7] Sainte-Rose and Chumass / 1996 [8] Teo and Jones/ 1996  [12] Goumnerova and Frim / 1997 [47] Baskin et al / 1998 [30] Brockmeyer et al / 1998 [13] Buxton et al / 1998 [16] Buxton et al / 1998 [15] Tuli et al / 1998 [37] Gangemi et al / 1999 [10] Cinalli et al / 1999 [4] Hopf et al / 1999 [9] Tisell et al / 2000 [26]

(4 M–17 Y) (PNB–78 Y) N/R 5.3 Y 11 Y (1 W–32 Y) 11.2 Y (2 D–36 Y) 17.3 Y (1.5–49 Y) 8.1 Y (1 D–29.5Y ) 3.7 M (0 M–10 M) 2 M (0–11 M)* All PNB 8.1 Y (0 M–18 Y) 31 Y (7 D–81 Y) NR (1 M–18 Y) 36 Y (3 W–77 Y) 48 Y (17–80 Y)

8% 7% 5% N/R 3% 9% 12% 6% 15% 21% N/R 12% N/R 6% N/R

Procedure abort rate

Follow-up mean (range)

16% 9% 6% N/R 9% N/R N/R 26% 0.4% 11% N/R

N/R 27 M (3 M–7 Y) N/R 1.8 Y 32 M (1 l –17 Y) 17 M (7 l –44 M) (21.4 M) 24.2M (15 l –69 M) N/R (6 l –42 M) (6 l –42 M) N/R (1 Y–11 Y) 28 M (12 l –54 M) 2.1 Y (4 D–9 Y) 26 M (3 l –71 l) 37 M (3 M–5 Y)

6% 2% N/R

Success rate (%) by etiology (n) Tumor/AS

Dysraphic

PHH/PIH

59% 68% 80% 81%

40% (5) 40% (10) 52% (21)

0% (2)

(17) (19) (25) (82)

Other (n-etiology)

72% (69) 70% (20) 59% (34) 57% (7) 43% (7) 66% (32) 91% (110) 86% (119) 83% (82) 50% (18)

0% (1) 50% (16) 0% (2)

0% (7) 10% (10) 30% (10)

100% (2-IDO) 64% (22-SVS) 20% (5-IDO)

63% (8)

Abbreviations:  AS aqueductal stenosis; D, days; IDO, idivpathie hydrocephalues; m, months; N/R, not reported; MMC, myelomeningocele, PHH post hemorrhagic hydrocephalus; PIH post infectious hydrocephalus; PNB, Premature newborn, SC; shunt complications (intractable shunt infection/malfunction); SVS, slit-ventricle syndrome; W, weeks; Y, year’s. * All patients born prematurely: mean age at birth was 31.9 weeks (range: 26–36 weeks).

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the techniques necessary to improve outcome further. Radiographic confirmation may also help to define indications with more subjective outcomes, for example, the observation of less fulminant shunt malfunctions in patients after ventriculostomy [11]. The authors use postoperative MRI imaging with sagittal T2-weighted images or cine MRI to confirm ventriculostomy flow and assess ventricular size 3 to 6 months after surgery. The absence of a flow void, although occasionally present in patients with good clinical outcome, was present in 12 of 13 patients presenting with delayed treatment failure in the series by Cinalli et al [4]. Increasing head circumference, signs and symptoms of elevated ICP, or evidence of CSF egress at the ventriculostomy incision site generally heralds early failures. Because of the risk of delayed failure of ETV, and the potential mortality if  this is unrecognized, we recommend that these patients use medical alert bracelets or wallet identification cards. A low threshold of suspicion for reimaging these patients should be followed, especially for the first 5 years after ETV. Families and caregivers are given the same education as for patients with shunts regarding symptoms of  failure. Education and regular follow-up are

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case of ETV with an average of 2.1 years of  follow-up (range: 4 days to 9 years). The overall functional ventriculostomy rate for the study was 72% at 6 years, without significant differences in the long-term results between the stereotactic and endoscopic groups [4]. Cine PC MRI studies on 15 patients up to 17 years after stereotactic ventriculostomy confirmed long-term patency (range: 10–  17 years, median = 14.3 years) [4].   No failures were reported in either group after 5 years of  follow-up. Additionally, 7 of 9 patients failing ventriculostomy with radiographically proven obstruction of the stoma had successful repeat ventriculostomies. Long-term data on ETV outcomes are only now beginning to emerge, and comparison to known outcomes of standard shunting procedures will be instrumental in defining the indications for initial treatment with ETV and the management of treatment failures. Summary

ETV is emerging as the treatment of choice for aqueductal stenosis caused by anatomic, inflammatory, and selected neoplastic etiologies. The technique has also proven useful in the pathologic diagnosis and treatment of these conditions

M  .R  . I    a  n  t    o  s   c   a  e   t    a  l      /    N  e   ur   o  s   ur   g  C  l     i    n  N A  m 1   5   (  2   0   0   4   )   6   7  –  7   5 

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the techniques necessary to improve outcome further. Radiographic confirmation may also help to define indications with more subjective outcomes, for example, the observation of less fulminant shunt malfunctions in patients after ventriculostomy [11]. The authors use postoperative MRI imaging with sagittal T2-weighted images or cine MRI to confirm ventriculostomy flow and assess ventricular size 3 to 6 months after surgery. The absence of a flow void, although occasionally present in patients with good clinical outcome, was present in 12 of 13 patients presenting with delayed treatment failure in the series by Cinalli et al [4]. Increasing head circumference, signs and symptoms of elevated ICP, or evidence of CSF egress at the ventriculostomy incision site generally heralds early failures. Because of the risk of delayed failure of ETV, and the potential mortality if  this is unrecognized, we recommend that these patients use medical alert bracelets or wallet identification cards. A low threshold of suspicion for reimaging these patients should be followed, especially for the first 5 years after ETV. Families and caregivers are given the same education as for patients with shunts regarding symptoms of  failure. Education and regular follow-up are important to counteract the false sense of security that may arise in the absence of a shunt. Failure of endoscopic third ventriculostomy

Studies of ETV are currently limited to studies with an average of less than 5 years of follow-up. These studies have documented early (1 year) postoperative failures. Early failures are more frequently reported in patients less than 6 months of age  [4,15,16].  Buxton et al [15,16]   have reported a mean time to failure in patients younger than 1 year of age of 1.36 months. Multiple authors have reported ‘‘late failures,’’ where the ventriculostomy closes, sometimes years after surgery [4,7,9,24,26]. Obstruction of the ventriculostomy by a gliotic scar or arachnoid membranes has been described  [31,51]. Rare cases of sudden death after late failure of ETV have been reported [52]. Although the long-term results of ETV are largely unknown, studies that include long-term follow-up on stereotactic ventriculostomy cases are likely applicable to ETV. Cinalli et al’s recent report [4]   included 94 cases of stereotactic ventriculostomy with an average of 6.32 years of  follow-up (range: 20 days to 17.4 years) and 119

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case of ETV with an average of 2.1 years of  follow-up (range: 4 days to 9 years). The overall functional ventriculostomy rate for the study was 72% at 6 years, without significant differences in the long-term results between the stereotactic and endoscopic groups [4]. Cine PC MRI studies on 15 patients up to 17 years after stereotactic ventriculostomy confirmed long-term patency (range: 10–  17 years, median = 14.3 years) [4].   No failures were reported in either group after 5 years of  follow-up. Additionally, 7 of 9 patients failing ventriculostomy with radiographically proven obstruction of the stoma had successful repeat ventriculostomies. Long-term data on ETV outcomes are only now beginning to emerge, and comparison to known outcomes of standard shunting procedures will be instrumental in defining the indications for initial treatment with ETV and the management of treatment failures. Summary

ETV is emerging as the treatment of choice for aqueductal stenosis caused by anatomic, inflammatory, and selected neoplastic etiologies. The technique has also proven useful in the pathologic diagnosis and treatment of these conditions [53–56]. Long-term results of this procedure and comparison to standard shunting procedures are necessary to define indications for patients with pathologic findings in the intermediate response groups. Development of new studies for preoperative assessment of CSF absorptive capacity and quantitative postoperative measures of  ventriculostomy function would be invaluable additions to our ability to assess candidates for this procedure and their eventual outcome. Further study and technical refinements will, no doubt, lead to many more potential uses for these procedures in the treatment of hydrocephalus and its associated etiologies. The challenge for neurosurgeons will be to define the operative indications and outcomes, while refining techniques for safely performing these useful procedures. References [1] Sainte-Rose C, Hoffman HJ, Hirsch JF. Shunt failure. Concepts Pediatr Neurosurg 1989;9:7–20. [2] Hoppe-Hirsch E, et al. Late outcome of the surgical treatment of hydrocephalus. Childs Nerv Syst 1998; 14(3):97–9. [3] Drake JM. Ventriculostomy for treatment of  hydrocephalus. Neurosurg Clin North Am 1993; 4(4):657–66.

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[4] Cinalli G, et al. Failure of third ventriculostomy in the treatment of aqueductal stenosis in children. J Neurosurg 1999;90(3):448–54. [5] Kelly PJ. Stereotactic third ventriculostomy in patients with nontumoral adolescent/adult onset aqueductal stenosis and symptomatic hydrocephalus [see comments]. J Neurosurg 1991;75(6): 865–73. [6] Jones RF, et al. Neuroendoscopic third ventriculostomy. In: Manwaring KH, Crone KR, editors. Neuroendoscopy, vol. 1. New York: Mary Ann Liebert; 1992. p. 63–77. [7] Jones RF, et al. The current status of endoscopic third ventriculostomy in the management of noncommunicating hydrocephalus. Minim Invasive Neurosurg 1994;37(1):28–36. [8] Sainte-Rose C, Chumas P. Endoscopic third ventriculostomy. Tech Neurosurg 1996;1:176–84. [9] Hopf NJ, et al. Endoscopic third ventriculostomy: outcome analysis of 100 consecutive procedures [see comments]. Neurosurgery 1999;44(4):795–806. [10] Gangemi M, et al. Endoscopic third ventriculostomy for hydrocephalus. Minim Invasive Neurosurg 1999;42(3):128–32. [11] Jones RF, Stening WA, Brydon M. Endoscopic third ventriculostomy. Neurosurgery 1990;26(1): 86–92. [12] Teo C, Jones R. Management of hydrocephalus by endoscopic third ventriculostomy in patients with myelomeningocele. Pediatr Neurosurg 1996;25(2): 57–63. [13] Brockmeyer D, et al. Endoscopic third ventriculostomy: an outcome analysis. Pediatr Neurosurg 1998;28:236–40. [14] Jaksche H, Loew F. Burr hole third ventriculocisternostomy. An unpopularbut effective procedure for treatment of certain forms of occlusive hydrocephalus. Acta Neurochir (Wien) 1986;79:48–51. [15] Buxton N, et al. Neuroendoscopy in the premature population. Childs Nerv Syst 1998;14(11):649–52. [16] Buxton N, et al. Neuroendoscopic third ventriculostomy in patients less than 1 year old. Pediatr Neurosurg 1998;29(2):73–6. [17] Natelson SE. Early third ventriculostomy in meningomyelocele infants—shunt independence? Childs Brain 1981;8(5):321–5. [18] Patterson RH Jr., Bergland RM. The selection of  patients for third ventriculostomy bases on experience with 33 operations. J Neurosurg 1968;29(3): 252–4. [19] Sayers MP, Kosnik EJ. Percutaneous third ventriculostomy: experience and technique. Childs Brain 1976;2(1):24–30. [20] Vries JK, Friedman WA. Postoperative evaluation of third ventriculostomy patients using 111inDTPA. Childs Brain 1980;6(4):200–5. [21] Jones RF, et al. Neuroendoscopic third ventriculostomy. A practical alternative to extracranial

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[38] Sainte-Rose C. Third ventriculostomy. In: Manwaring KH, Crone KR, editors. Neuroendoscopy, vol. 1. New York: Mary Ann Liebert; 1992. p. 47–62. [39] Sainte-Rose C, et al. Mechanical complications in shunts. Pediatr Neurosurg 1991;17:2–9. [40] Di Rocco C, Marchese E, Verladi F. A survey of the first complication of newly implanted CSF shunt devices for the treatment of nontumoral hydrocephalus. Cooperative survey of the 1991–1992 Education Committee on the ISPN. Childs Nerv Syst 1994;10(5):321–7. [41] Albright AL, Haines SJ, Taylor FH. Function of  parietal and frontal shunts in childhood hydrocephalus. J Neurosurg 1988;69:883–6. [42] Piatt JH Jr. Cerebrospinal fluid shunt failure: late is different from early. Pediatr Neurosurg 1995;23: 133–9. [43] Oka K, et al. The radiographic restoration of the ventricular system after third ventriculostomy. Minim Invasive Neurosurg 1995;38(4):158–62. [44] Schwartz TH, et al. Third ventriculostomy: postoperative ventricular size and outcome. Minim Invasive Neurosurg 1996;39(4):122–9. [45] Kulkarni AV, et al. Imaging correlates of successful endoscopic third ventriculostomy. J Neurosurg 2000;92(6):915–9. [46] Jack CR Jr., Kelly PJ. Stereotactic third ventriculostomy: assessment of patency with MR imaging. AJNR Am J Neuroradiol 1989;10(3):515–22. [47] Goumnerova LC, Frim DM. Treatment of hydrocephalus with third ventriculocisternostomy: out-

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come and CSF flow patterns. Pediatr Neurosurg 1997;27(3):149–52. Wilcock DJ, et al. Neuro-endoscopic third ventriculostomy: evaluation with magnetic resonance imaging. Clin Radiol 1997;52(1):50–4. Lev S, et al. Functional analysis of third ventriculostomy patency with phase-contrast MRI velocity measurements. Neuroradiology 1997;39(3): 175–9. Wilcock DJ, Jaspan T, Punt J. CSF flow through third ventriculostomy demonstrated with colour Doppler ultrasonography. Clin Radiol 1996;51(2): 127–9. Hirsch JF, et al. Stenosis of the aqueduct of Sylvius. Etiology and treatment. J Neurosurg Sci 1986; 30(1–2):29–39. Hader W, et al. Death following late failures of  third ventriculostomy in children: a report of 3 cases. J Neurosurg 2002, in press. Ellenbogen RG, Moores LE. Endoscopic management of a pineal and suprasellar germinoma with associated hydrocephalus: technical case report. Minim Invasive Neurosurg 1997;40(1):13–6. Drake J. Neuroendoscopy tumour biopsy. New York: Mary Ann Leibert; 1992. p. 103–9. Ferrer E, et al. Neuroendoscopic management of  pineal region tumours. Acta Neurochir (Wien) 1997;139(1):12–21. Oka K, et al. Endoneurosurgical treatment for hydrocephalus caused by intraventricular tumors. Childs Nerv Syst 1994;10(3):162–6.

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Neuro-oncologic applications of endoscopy Charles Teo, MBBS, FRACS a, Peter Nakaji, MDa,b,* a

Centre for Minimally Invasive Neurosurgery, Prince of Wales Hospital/University of New South Wales, Barker Street, Randwick, NSW 2031, Sydney, Australia b Division of Neurological Surgery University of California at San Diego Medical Center, San Diego, CA, USA

No other subspecialty of neurosurgery exemplifies the advantages of endoscopy more than neuro-oncology. From a pure technical standpoint, visualization is the  sine qua non of surgery. If a surgeon cannot see what he is doing, he is ineffective and dangerous. Cranial neurosurgery in particular is a constant struggle against poor visualization. In an attempt to minimize operative trauma, the surgeon aims to limit the size of the exposure and to avoid vigorous brain retraction. Meanwhile, the tumor/brain interface is often hard to distinguish, and the tumor often insinuates itself behind or between structures that cannot be sacrificed. Critical structures, such as cranial nerves, vessels, and eloquent brain tissue, may prohibit direct visual access to some parts of  the tumor. At the same time, in the case of the more benign tumors that occur in the cranial cavity, total excision is vital to the patient’s survival   [1,2].   Complete removal of an acoustic neuroma is nearly tantamount to cure. Other extra-axial tumors, such as craniopharyngiomas and meningiomas, also must be removed as completely as possible to reduce the incidence of  tumor recurrence. Because low-grade gliomas respond poorly to radiotherapy and chemotherapy, prognosis is directly related to the degree of tumor resection. Ependymomas are also historically insensitive to adjuvant therapies, and total macroscopic removal is paramount [3]. Any tool that improves visualization, thereby offering

* Corresponding author. E-mail address:   [email protected] (C. Teo).

patients a better surgical outcome, should be embraced by the neuro-oncologic surgeon. The endoscope is such a tool. It enhances the surgeon’s view by increasing illumination and magnification [4,5]. It allows the surgeon to view tumor remnants, such as those hidden behind the tentorial edge, a cranial nerve, or eloquent brain tissue. Once the tumor is removed, the surgeon can use the endoscope to assess the degree of  resection. Often, the same surgery can be performed through a smaller craniotomy by using the endoscope, in keeping with the concept of  minimally invasive yet maximally effective surgery [6]. Adjunctive procedures, such as third ventriculostomy and septostomy, can be performed through the same access to manage related problems, such as secondary hydrocephalus. Endoscopic tumor removal or cerebrospinal fluid (CSF) diversion may allow patients to avoid shunt placement. Finally, the endoscope is an excellent teaching tool. The anatomic definition and unique angles of view available to the endoscope help residents with their understanding of operations and help to illuminate anatomicopathologic concepts underlying neuro-oncologic surgery. Applications

Applications for the endoscope are limited only by one’s imagination. Initially used for intraventricular surgery alone, the endoscope has also become an invaluable tool in the surgical management of extra-axial pathologic processes. It is being increasingly applied as an adjunct to the removal of masses in the subarachnoid space. Within the ventricle, the endoscope is a versatile tool for diagnosing and treating tumors and associated problems of CSF circulation.

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We discuss the neuro-oncologic applications of  endoscopy under the following headings: 1. 2. 3. 4. 5.

Ventriculoscopy Management of secondary hydrocephalus Endoscopic tumor biopsy Endoscopic intraventricular tumor resection Endoscope-assisted microsurgery

Ventriculoscopy The prognosis of some primary intracranial tumors is dependent on the presence or absence of  ependymal spread of tumor. Patients with primitive neuroectodermal tumors, for example, fall into the high-risk group rather than the low-risk group if there is evidence of spinal or ventricular ependymal tumor involvement. Although MRI is reliable in the detection of ependymal tumor spread in most cases, some patients may have ependymal spread without radiologic evidence [7]. Ventriculoscopy can be more sensitive than MRI with little added morbidity. Through a frontal or parietal burr hole, one can access the lateral ventricle, examine the surface, document any findings with color photography, and even biopsy suspicious areas. This can be performed with a 10minute general anesthetic, which is substantially less time than is needed for an MRI examination. Furthermore, if present, definitive treatment of  CSF obstruction can be achieved by either third ventriculostomy or tumor resection at the same sitting. Fig. 1 shows endoscopic pictures of the lateral ventricle of a patient with a pineal primitive neuroectodermal tumor who had no imaging evidence of ependymal tumor involvement. The patient had an endoscopic third ventriculostomy (ETV) and, thereafter, chemotherapy. The response to chemotherapy was well documented by ventriculoscopy, thereby allowing the patient to be a candidate for high-dose chemotherapy and autologous bone marrow transplantation. Management of secondary hydrocephalus The management of secondary hydrocephalus is a controversial area of pediatric neurooncology. There are several different treatment

paradigms. A popular option would be to place a temporary external CSF drain as a primary procedure, remove the obstruction, and then, as a secondary procedure, shunt those patients who continue to require CSF drainage. Another option is to insert a permanent shunt as a primary procedure before tumor resection. A third option would be to perform an ETV either primarily or secondarily. The arguments in favor of the early management of the hydrocephalus are as follows: 1. There are some circumstances in which the surgeon cannot definitively treat the primary cause of obstruction, and CSF diversion is the only option. These patients may present with symptoms of raised intracranial pressure and impending brain herniation. 2. The surgeon may need more time for preoperative assessment (eg, the patient with a bleeding diathesis, the patient who needs staging of his or her tumor). 3. The primary CSF diversionary procedure may be definitive. An example of this is the patient with a tectal glioma, in whom symptoms are usually secondary to hydrocephalus and not the primary tumor. 4. On rare occasions, MRI reveals pathology previously ‘‘hidden’’ by the hydrocephalus (Fig. 2). The patient in  Fig. 2 presented with severe intracranial hypertension and was thought to have hydrocephalus from aqueductal stenosis. After ETV, it became clear that the obstruction was secondary to a pineal region tumor. 5. Some surgeons believe that operative conditions for the definitive surgery are better after prior drainage of CSF. The arguments against initial treatment of the hydrocephalus are as follows: 1. Many patients do not have a permanent CSF flow problem; therefore, some shunts are placed unnecessarily. Of course, this is not a concern when temporary CSF diversion is undertaken using external ventricular drainage. 2. If the obstruction is caused by a posterior fossa tumor, there is potential for upward

c

Fig. 1. (A) The ependyma is frosted with plaque-like tumor that was not seen on MRI. (B) After conventional chemotherapy, the clinical response is documented ventriculoscopically. (C ) After high-dose chemotherapy and autologous bone marrow transplantation, the ependymal surface is clear of visible tumor.

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Fig. 2. (A) The patient is an 11-year-old boy with profound hydrocephalus of unclear etiology. (B) After an endoscopic third ventriculostomy and resolution of the hydrocephalus, an occult pineal region tumor is now apparent.

herniation with decompression of the supratentorial CSF spaces. 3. There is a risk of infection with external drainage. 4. There is a risk of spreading tumor cells to the peritoneum with extracranial CSF diversion. ETV is a reasonable option if the surgeon decides to treat the secondary hydrocephalus before definitive treatment of the primary tumor. This operation can be done through a standard frontal burr hole similar to that which would be made for insertion of an external ventricular drain (Fig. 3). Similarly, CSF samples can be taken at the time of surgery, and one may also explore the third ventricle, taking biopsies if necessary. There is no risk of ongoing infection as can be seen with external drainage; no risk of seeding as has been documented with ventriculoperitoneal shunting; and no risk of upward herniation, which can potentially happen with any extracranial diversionary procedure. Finally, ETV may be the definitive treatment if the obstruction is caused by a tumor that does not require removal, such as a tectal plate tumor.

Endoscopic septum pellucidotomy may also be the definitive treatment for some types of hydrocephalus. Fig. 4 shows the MRI scan of an elderly lady who presented with headaches and disorientation. She was found to have a cystic tumor of  the third ventricle causing obstruction of only one of the lateral ventricles. The provisional diagnosis was a craniopharyngioma, and she underwent endoscopic cyst fenestration and drainage, followed by septum pellucidotomy. The postoperative scans showed complete resolution of  the unilateral hydrocephalus and shrinkage of  the cystic component of the biopsy-proven craniopharyngioma. Technical notes The technique of ETV is described in elsewhere in this issue. There are a few precautions when performing ETV for hydrocephalus secondary to a tumor. First, the anatomy may be altered. A tumor like a pontine glioma may distort the floor of the third ventricle and displace the basilar artery forward so that the safe zone to penetrate the floor is a submillimetric area just

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Fig 3. (A) The endoscopic third ventriculostomy is performed in the third ventricular floor just behind the mamillary bodies. The close relation to the basilar apex is illustrated. ( B) In chronic hydrocephalus, the third ventricular floor is thin and visualization of the mamillary bodies is easy. ( C ) In acute hydrocephalus, it may not be possible to see the usual landmarks. The floor is thicker, and a sharp technique may be necessary. In this instance, more experience is required to identify the proper location for the ventriculostomy safely.

behind the dorsum sella and just in front of the basilar bifurcation. Using a blunt technique to create the stoma would be prudent in such a case. Second, hydrocephalus resulting from tumor obstruction may be relatively acute in onset. When this is the case, the floor of the third ventricle is often opaque and nonattenuated. This makes penetration more difficult and invariably requires a sharper technique without visualization of the underlying neurovascular structures. This ‘‘blind’’ fenestration through a thick floor can be hazardous and should not be undertaken by the novice endoscopist. Third, ETV combined with biopsy of posterior third ventricular tumors cannot be done through the standard ETV burr hole. The ideal trajectory for the anterior third ventricular floor is just anterior to the coronal suture, whereas that for the posterior third ventricle is just posterior to the hairline or 8 cm

behind the nasion and 3 cm from the midline. The foramen of Monro is sometimes expanded enough to allow access to both parts of the third ventricle through a single burr hole placed between the coronal suture and the hairline. This may be assessed before surgery by close inspection of the MRI. A comment should be made about the use of  flexible fiberscopes. It is true that with a rigid endoscope, it is difficult to perform an ETV and biopsy of a posterior third ventricular tumor through the same burr hole. Nonetheless, we believe that a rigid endoscope is preferable to using a flexible scope insofar as it can be impossible to be sure where the back of the flexible endoscope is. The risk of complications in most hands is consequently higher with flexible endoscopes. It is our personal practice not to use flexible endoscopes in the head.

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Fig. 4. Cystic craniopharyngioma in an elderly woman who presented with high intracranial pressure. The cyst was fenestrated endoscopically, and a septum pellucidotomy was performed. The patient’s symptoms resolved, and she did not require shunting.

Endoscopic tumor biopsy There are no studies showing that endoscopic tumor biopsy is any better than stereotactic needle biopsy. Anecdotally, however, there seem to be definite advantages to this technique. Endoscopic biopsy should be considered when the tumor is either within the ventricle or at least presenting to the ventricular surface. The advantages are as follows: 1. Direct visualization of the tumor allows more accurate and safer sampling. A region for biopsy can be chosen under endoscopic vision, and vessels can be avoided. 2. The specimen obtained is larger and not subjected to as much mechanical artifact. It does not need to be sucked up a needle or manipulated. 3. Any resultant bleeding can be stopped by either coagulation or packing under direct visualization. 4. If the tumor is relatively avascular, it may be removed totally by endoscopic techniques. 5. Other procedures can be performed at the same operation (eg, ETV, septum pellucidotomy). Examples of tumors that are typically approachable endoscopically are colloid cysts, subependymal giant cell astrocytomas, other

Fig. 5. Biopsy of a tumor in the posterior wall of the third ventricle with grasping forceps. Bleeding after such a biopsy can usually be managed with irrigation alone.

low- (including tectal gliomas) and high-grade gliomas [Fig. 5], central neurocytomas, subependymomas, and choroid plexus tumors and cysts [8]. Most of these tumors are relatively avascular, and hemorrhage is rarely a problem. The burr hole is made so that the scope enters the ventricle as far from the tumor as possible and so that the scope is directly viewing the tumor rather than peering from around a corner. The distal approach allows the surgeon to orient himself by identifying normal anatomic structures before encountering the abnormal anatomy. Because most of the distal part of the scope is within the ventricle, it also allows the surgeon to move the scope in multiple directions more freely without damaging the surrounding normal brain. Starting from farther away means that only relatively small excursions are necessary within the normal brain to visualize the entire target. Many surgeons are hesitant to employ endoscopy for tumors because of the fear of bleeding. Almost all bleeding can be controlled with irrigation alone until the bleeding stops. If bipolar and monopolar instruments are available, they can be used, but they are often ineffective. Patience and copious irrigation are the keys. For tumors that are primarily intra-axial, there are few advantages of endoscopic biopsy over standard stereotactic techniques. Some extra-axial tumors that require biopsy, such as those that might be seen around the circle of Willis and suprasellar region, are well suited to this technique, however. For these tumors, stereotactic techniques are too dangerous and standard open

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craniotomy is extremely invasive. Endoscopic biopsy allows a minimally invasive approach with excellent visualization and safety. The opening is made through a supraorbital brow incision and a small frontal craniotomy. The suprasellar region is then approached using standard microsurgical technique, and the scope is introduced when the cisterns have been opened. Biopsies should be taken with straight or angled cup forceps passed along the scope and not down a working channel. The instruments should always be passed ahead of  the endoscope so that their progress can be observed. Blind passage of the instruments into the endoscope’s field of view risks damaging structures located behind the tip. Endoscopic intraventricular tumor resection Not all intraventricular tumors should be approached endoscopically. The ideal tumor for endoscopic consideration has the following characteristics: 1. Moderate to low vascularity 2. Soft consistency

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3. Less than 2 cm in diameter [9] 4. Associated secondary hydrocephalus 5. Histologically low grade 6. Situated in the lateral ventricle Clearly, from this list of desirable features, almost all patients with colloid cysts are appropriate candidates for this technique. The results with these tumors are often excellent, and in at least one study, endoscopic resection was clearly superior to microsurgery (Figs. 6 and 7)   [10]. Other tumors that are well suited to total endoscopic removal are subependymal giant cell astrocytomas around the frontal horn of the lateral ventricle, other low-grade gliomas that are exophytic into the ventricles, central neurocytoma, small choroid plexus tumors, and the purely intraventricular craniopharyngioma. There are few articles in the neurosurgical literature on the application of endoscopy for the removal of intraventricular tumors. Most of the experience with endoscopic tumor resection has specifically addressed the removal of colloid cysts [10–12]. Whichever technique is used, patient

Fig. 6. Pre-endoscopic (A) and postendoscopic (B) removal of a colloid cyst. Note resolution of the hydrocephalus and preservation of the normal anatomy.

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Fig. 7. (A) Initially narrow view of the foramen of Monro. The choroid plexus is to the left of the image, with the septal vein located superiorly. (B) The choroid plexus is coagulated with monopolar cautery. The cyst is now clearly visible as a gray structure through the foramen. ( C ) View of the foramen of Monro after removal of the colloid cyst. The fornix is seen to the right of the image, the septal vein superiorly, the thalamostriate vein to the lower left, and the choroid plexus to the upper left.

selection is controversial. For tumors in the vicinity of the foramen of Monro, the presence of hydrocephalus is an absolute indication for some form of surgical intervention. Headache in the absence of hydrocephalus can be a sign of  intermittent obstruction of the foramen of Monro or some other part of the ventricular system, and patients should be informed of the possibility of  insidious onset of hydrocephalus and sudden death. Another indication for surgery would be radiologic progression either in size or enhancing characteristics. This is particularly true for giant cell subependymal astrocytomas that are located in the frontal horn of the lateral ventricle. Whatever tumor is approached, some basic

principles apply. An approach trajectory that avoids eloquent structures but allows a good view of the tumor is essential. Most intraventricular tumors are dealt with in the same fashion. Once good visualization is achieved, the outside of the tumor is coagulated with either monopolar electrocautery or a laser. Copious irrigation is used to clear blood and debris and to prevent too much heat from building up inside the ventricle. If  there is a cyst, it is opened and drained. The contents are removed via suction or piecemeal. The remaining wall is coagulated and removed piecemeal. Hemostasis is obtained with copious irrigation. The scope is withdrawn while inspecting the tract for intraparenchymal bleeding. A

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small wick of Gelfoam is placed in the cortical opening to prevent CSF leakage from the ventricle. Endoscopic colloid cyst removal  The colloid cyst is the prototypical intraventricular tumor; as such, we discuss its removal in some detail. The colloid cyst represents the ideal intraventricular tumor that can be completely resected via the endoscopic approach. The goals of surgery are to extirpate totally the cyst wall, to avoid spillage of the cyst contents, to minimize trauma to the adjacent structures (ie, fornices, walls of the third ventricle), to spare venous structures, and to minimize cortical damage along the approach route. The first two goals are more difficult with the endoscope than with open surgery, whereas the last three are actually easier to achieve. The lower morbidity and shorter operating time form the rationale for the endoscopic approach. In practice, complete cyst drainage and removal can be better accomplished endoscopically than microsurgically once the skill is mastered. The choice of endoscopy as the treatment modality should depend on (1) proper patient selection, (2) adequacy of the equipment, and (3) adequacy of the surgeon’s experience and preparation. Patient selection Almost all patients with colloid cysts are good candidates for the endoscopic approach. We encourage endoscopic removal as the preferred first procedure, with the option of craniotomy if  endoscopy is unsuccessful. In fact, a wide range of  management strategies and therapeutic options are available to treat patients with colloid cysts. These include observation, shunting of the lateral ventricles, stereotactic aspiration, open transcortical or transcallosal resection, and endoscopic removal. For a patient who presents nonemergently, such as with an incidentally discovered colloid cyst, it is important to discuss all options. Nonetheless, given the risk of acute CSF obstruction, herniation, and death associated with these masses, we recommend definitive treatment by the least morbid route, which is via the endoscope. The main technical factor that affects colloid cyst removal is the density of the cyst contents. This can best be estimated using noncontrast CT. Hypodense or isodense contents are usually fairly liquid and can be removed through the small apertures of the endoscope without difficulty  [13]. A small suction catheter attached to a 10- or 20mL syringe may help in this regard. Hyperdense

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cysts may have more tenacious contents, which can prove more difficult to remove with the endoscope. Cup forceps may need to be used to remove the contents of these denser cysts piecemeal. On MRI, high signal on T1-weighted imaging correlates with higher cholesterol content   [14],   thicker consistency, and more difficult removal. Technique The patient is positioned straight supine with the head up 45 . A single burr hole is placed on the nondominant side 8 cm behind the nasion and approximately 7 cm lateral to the midline. This is farther lateral than previously published by the senior author (C.T.), a modification that has allowed better removal of the component of the cyst in the roof of the third ventricle. A strip shave is made for the incision, which is 4 cm long and coronally oriented over the site of the burr hole. Preparations should be made to preserve the option of converting to an open craniotomy, with a craniotomy tray and microscope available. If the ventricles are small, frameless stereotactic guidance is used to guide the placement of the endoscope sheath and trocar. Otherwise, freehand cannulation of the ventricle with a ventricular needle precedes placement of the sheath. A 2- to 5-mm 30 rigid endoscope with at least one working channel is placed down into the ventricle. The boundaries of the foramen of  Monro are appreciated: the fornix above and anteriorly, the choroid plexus and the septal and thalamostriate veins exiting posteroinferiorly, and the anterior nucleus of the thalamus located below. The foramen of Monro is normally 0.3 to 0.8 mm in diameter. In the presence of a colloid cyst, it is variably expanded. The cyst is attached to the roof of the anterior third ventricle, and its anterolateral surface usually bulges into or through the visible part of the foramen. Every effort is made to preserve all normal structures in removing a colloid cyst. Generally, this can be accomplished; however, three structures may be sacrificed, if necessary, to provide widened access to the tumor, in descending order of preference: choroid plexus, the thalamostriate vein, and the ipsilateral fornix. The first structure is sacrificed with impunity, but sacrifice of the latter two should only be considered if all other options have been exhausted. If choroid plexus obstructs the view of the cyst, it can be coagulated with a monopolar probe and dissected free from the foramen without difficulty. No morbidity attends 

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this maneuver. The thalamostriate vein may be large and present an obstacle. Every effort should be made to preserve the vein. Past authors have warned of potentially devastating consequences from sacrificing a thalamostriate vein, but this has not been borne out in subsequent reports by other authors or in our own experience. The primary reason not to sacrifice the vein is that it is far more difficult to do this safely using the endoscope than microsurgically. The bleeding from the vein can be daunting. Fortunately, sacrifice of the vein rarely becomes necessary. Last, although it is not preferable, a thinned-out ipsilateral fornix may need to be sacrificed to provide adequate access to a large colloid cyst. Permanent short-term memory loss is sometimes a consequence of this maneuver. Other structures that may be pitfalls in this case are the thalamus, the internal capsule, and the head of the caudate, all of which must not be harmed. The internal capsule runs in the groove between these other two structures; damage to this structure during endoscopic procedures has resulted in contralateral hemiparesis. Once exposed, the surface of the cyst is gently devascularized with electrocautery. Although a laser may also be used for this role, the results are not superior to monopolar electrocautery despite the greater expense and complexity. The wall of  the cyst is then pierced with the monopolar probe, and the contents are removed piecemeal or with suction attached to a hand syringe once inside the cyst. After it is emptied, the cyst wall is coagulated and removed piecemeal. Care is taken not to provide excessive traction on the roof of the third ventricle, because severe bleeding from the internal cerebral veins can result. Other authors have written that a small amount of the cyst wall may have to be left on the third ventricle roof and the columns of the fornix, but this has at times been associated with recurrence. In the senior author’s personal series, complete removal was possible in 24 of 26 cases; the remaining two patients underwent transcortical removal of the residual. From the anterolateral approach described here, the 30 endoscope affords a view of  the roof of the third ventricle that can help to confirm complete removal of the cyst wall. It has not been necessary to place drains at the time of surgery or to maintain them after surgery. Most authors with experience in this area have used drains in their early cases and, over time, moved away from using them. A drain may be considered in a patient in whom the risk of sudden 

decompensation because of postoperative hydrocephalus is believed to be high. Ultimately, it is up to the surgeon to make an individual assessment on a case-by-case basis. In the senior author’s personal series, no patient has required placement of a permanent ventricular shunt. Variations in technique Endoscopic removal of colloid cysts using a flexible fiberscope has been described. Although this approach is possible, it offers no advantage over rigid endoscopy, has a substantially higher learning curve, requires more coordination with an assistant, and is associated with greater risk. This approach is absolutely contraindicated for any surgeon not already familiar with the fiberscope. The technique described previously is a oneportal technique. We have found this approach adequate in most cases. From the anterolateral approach, both fornices and the roof of the third ventricle can be seen from one side. A two-portal ipsilateral technique has been described by Jimenez  [15],   but we have not found this to add much to the procedure and believe that the addition of more portals goes against the goals of a minimally invasive approach. Complication avoidance Copious irrigation is important throughout the procedure to maintain good visualization and dissipate heat generated by the electrocautery. We use 20-mL syringes to provide pulsed handinjected irrigation. This allows good feedback as to how much pressure is being generated as well as rapid adjustment of irrigation depending on local conditions. This method does necessitate frequent changing of syringes throughout the case. It is important that a good path for egress of CSF be maintained so that fluid does not build up under pressure during the procedure. Herniation has been described as a result of induced hydrocephalus in this setting. A tube attached to the outlet port, which can be raised or lowered, permits the ‘‘pop-off’’ pressure to be varied, allowing the amount of ventricular dilatation to be controlled. Lactated Ringer’s solution is used as the irrigation solution. It is slightly hypo-osmolar (276 mOsm) but is physiologically more like CSF than normal saline. Some authors have described postoperative confusion for 24 to 48 hours after procedures in which normal saline (308 mOsm) is used as the irrigant. There is no widely commercially available CSF substitute at present.

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Blee Bleedi ding ng from from the the coll colloi oid d cyst cyst or chor choroi oid d plex plexus us shou should ld be addr addres esse sed d with with mono monopo pola larr coagul coagulati ation on.. All other other bleed bleeding ing should should be addressed with irrigation. Almost all bleeding stops with irrigation alone if the irrigation is continued long enough; this may mean continuous irrigation for as long as 20 minutes. The value of copious irriga irrigatio tion n canno cannott be overem overempha phasiz sized. ed. With With patience tience,, almost almost any degree degree of bleedi bleeding ng can concontrolled in this manner. If this is not adequate, in some some case cases, s, blee bleedi ding ng vess vessel elss may may have have to be sacrificed with the use of electrocautery. In cases of genera generaliz lized ed ooze, ooze, a balloo balloon n may be inflate inflated d gently in the foramen of Monro or the endoscope itself may be used to provide focal compression. Other techniques for controlling difficult bleeding include irrigation with cool saline (which causes vasoconst vasoconstricti riction), on), draining the CSF to perform perform ‘‘dry field’’ coagulation, and raising the height of  the drain until until the intracrani intracranial al pressure pressure exceeds venous pressure. If nothing stops the bleeding, the procedure may be need to be converted to an open craniotomy. In our experience, this last step has never actually been necessary. necessary. Conclusions The endoscopic removal of colloid cysts is one of the most most satisf satisfyin ying g of neuroe neuroendo ndosco scopic pic proprocedu cedure res. s. Once Once some some expe experi rien ence ce is gai gaine ned, d, the the technique is faster and less morbid than the open appr approa oach ch.. Skil Skills ls obta obtain ined ed work workin ing g on thes thesee tumors provide the foundation for the techniques that allow the removal of other other intraventr intraventricula icularr tumors. The princi principle pless discus discussed sed here here can be applie applied d to any mass that meets the indications for endoscopic scopic remova removal. l. The follow following ing points points reiter reiterate ate the techniques applicable to the removal of intraventricular tumors in general: 1. Have the correct correct instrume instrumentati ntation on availa available. ble. Essential tools are a pair of grabbing forceps and and scis scisso sors rs,, a good good assi assist stan antt or a scop scopeehold holdin ing g devi device ce so you you can can work work with with two two hands, hands, a coagul coagulati ation on device device (eithe (eitherr mono mono-polar or bipolar), a means of irrigating, and straight and 30 angled scopes. 2. Make the ventricular entry as far away from the tumor as possible. The further the tip of  the scope is from the burr hole, the smaller is the angle required to displace the end of  the scope a giv given en dista distance nce.. This This allows allows the surgeon to angle the rigid scope in different dire direct ctio ions ns with withou outt causi causing ng as much much brai brain n 

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injury as would otherwise occur. It also gives the surgeon a chance to view the tumor from a distance, an important point when there is excessive bleeding. A good amount of ventricle between between the entry point point and the tumor tumor means the scope can be pulled back from the bleeding site without exiting the ventricle. 3. Maintai Maintain n the ventri ventricul cular ar volum volumee to ensure ensure a workab workable le opera operativ tivee field. field. This This is achiev achieved ed with with contin continuo uous us irriga irrigatio tion. n. Of course course,, it is impe impera rati tive ve to make make sure sure ther theree is an ununimpe impede ded d egre egress ss of fluid fluid so as to prev preven entt iatrogenic intracranial hypertension. A channel on the endoscope leading to an open port, serving as a pop-off valve, may be useful in this regard. 4. Ma Mana nage ge hemo hemorr rrha hage ge with with the the foll follow owin ing g techniques techniques:: copious copious irrig irrigation ation usually usually clears the the oper operat ativ ivee field field of bloo blood d and and allo allow w the the surgeon to continue without using the other tech techni niqu ques es.. It is impo import rtan antt to keep keep the the tem temperat eratu ure of the fluid uid clos closee to body temperature and the composition as close to CSF as possible. Lactated Ringer’s solution is preferred because it is the closest to isotonic of the relati relativel vely y ava availa ilable ble fluids. fluids. Irr Irriga igatio tion n sett settle less almo almost st all all blee bleedi ding ng even eventu tual ally ly,, alalthough it may take upward of 20 minutes of  contin continuou uouss lav lavage age in some some cases. cases. Using Using the scop scopee or an inst instru rume ment nt to tamp tampon onad adee the the blee bleede derr can can be effec effecti tive ve,, espe especi cial ally ly when when combined with head-up elevation and irrigation. The next technique is to attempt direct coagul coagulati ation on with with either either a bipola bipolarr or monomonopolar instrument. This technique can be quite a challenge given the obscuration of the field with blood, the mobile vessels, the presence of  adjacent vital structures, and the difficulty of  finding the exact bleeding point with a single instru instrumen ment. t. Finall Finally, y, if all these these techn techniqu iques es fail, the ventricle can be drained drained of CSF. This allows more effective bipolar and monopolar coagulation without clouding of the operative field. The obvious downside is the collapse of  the ventricular walls, resulting in constriction of the operativ operativee field. field. This This can be partia partially lly offset by injecting air into the ventricle, which keeps the walls apart if there is a good seal around the working channels and around the brain/scope interface. 5. Finally, it is imperative to keep in mind the patien patient’s t’s best best intere interests sts.. Large Large and vascula vascularr intrav intravent entric ricula ularr tumors tumors are difficul difficultt to remove move by pure pure endosc endoscopi opicc techn techniqu iques. es. The The

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operation can become long and tedious with more more bloo blood d loss loss and and risk risk to surr surrou ound ndin ing g eloqu eloquent ent brain brain tissue tissue than than a routin routinee micromicrosurgical approach. Do not hesitate to abandon the endoscope if you feel more confident usin using g a more more fami famili liar ar tech techni niqu que. e. Alwa Always ys rememb remember er the dictum dictum:: minima minimally lly invasi invasive ve and maximally effective.

Endoscope-assisted microsurgery Endoscope-assisted microsurgery is the area of  neur neuroe oend ndos osco copy py that that has has rece receiv ived ed the the leas leastt attention attention by neurosurg neurosurgeons eons but whose whose potential potential valu valuee to the the neur neuroo-on onco colo logi gicc surg surgeo eon n is the the greatest. Microsurgery itself evolved to maximize visualization and minimize retraction; endoscopy allows allows the neuros neurosurg urgeon eon to move move anothe anotherr step step further toward achieving these goals. With endoscopy, previously inaccessible or poorly accessible tumors located in the skull base, within narrow cavities, deep to key vascular or neural structures, or around corners in the intracranial space can be clearl clearly y visual visualize ized; d; once once visual visualize ized, d, they they can be resected. The introduction of the endoscope has the poten potentia tiall to revolu revolutio tioniz nizee the approa approach ch to certa certain in tumo tumorr type typess by allo allowi wing ng safe safe radi radica call removal. These techniques are particularly applicable cable to a wide wide rang rangee of trou troubl bles esom omee tumo tumors rs,, includ including ing but not limite limited d to sellar sellar tumors tumors,, including pituitary tumors, craniopharyngioma, and Rathke Rathke’s ’s cleft cleft cysts; cysts; clival clival chordo chordomas mas;; pineal pineal lesions, intraparenchymal tumors near the brain stem stem or cran crania iall base base;; acou acoust stic ic neur neurom omas as;; and and anteri anteriorl orly y or centra centrally lly locate located d poste posterio riorr fossa fossa tumors   [16,17]. [16,17]. At the point at which dissection must halt because of the failure of the microscope to prov provid idee an adeq adequa uate te view view,, the the endo endosc scop opee should be brought into play. A summ summar ary y of the the adva advant ntag ages es of the the endo endo-scope as an adjunct to microsurgery includes the following: 1. Better Better definit definition ion of the norma normall and pathopathologic logic anatom anatomy. y. The endosc endoscop opee can be used used to clar clarif ify y the the anat anatom omy y befo before re and and duri during ng tumor removal. Key neural or vascular structures tures can be identi identified fied and thereb thereby y spared spared.. This This may may be part partic icul ular arly ly impo import rtan antt when when worki working ng around around or within within the brain brain stem, stem, between small perforating vessels, or between the cranial nerves. 2. Iden Identi tific ficat atio ion n of port portio ions ns of the the tumo tumorr located behind or adherent to vital structures.

Some portions of tumor that are apparently inva invasi sive ve into into the the brai brain n have have brai brain/ n/tu tumo morr interfaces that can be identified when visualized ized at more more direct direct angles angles than than is possib possible le with the operating microscope alone. 3. Mi Mini nimi mizat zatio ion n of retr retrac acti tion on.. The The auth author orss seldom seldom employ employ any fixed fixed retrac retractor torss even even in the approach to extremely deep lesions. The endo endosc scop opee allo allows ws narr narrow ow corr corrid idor orss to be used, reducing the need to displace sensitive structures. 4. Assessing Assessing adequacy adequacy of tumor removal. removal. At the conclusio conclusion n of the procedure procedure,, endoscop endoscopic ic inspection allows a more accurate estimation of  the completeness of resection or, if complete resection cannot be achieved, documentation of wher wheree and and how how much uch resi residu dual al tumo tumorr remains. 5. As As a teac teachi hing ng tool tool.. The The endo endosc scop opee offer offerss a sup superio eriorr and and often ften novel vel view view of the the anatomy, which can be beneficial to residents’ unde unders rsta tand ndin ing g of the the surg surgic ical al appr approa oach ch.. Furt Furthe herm rmor ore, e, the the oper operat atin ing g surg surgeo eon n and and the the stud studen entt shar sharee the the same same view view,, whic which h is not not gene genera rall lly y true true even even with with an oper operat atin ing g microscope. The benefit contributed by adding endoscopy to a tradit tradition ional al cranio craniotom tomy y canno cannott be overem overem-phas phasiz ized ed.. Tumo Tumors rs freq freque uent ntly ly exte extend nd at acut acutee angl angles es to the the cran crania iall base base or to the the cort cortic ical al surf surface acess alon along g whic which h the the trad tradit itio iona nall surg surgic ical al app approac roach h is made ade (Fig. 8). Alth Althou ough gh thes thesee avenues are inaccessible to the microscope, which requires a direct line of sight, they are ideal for endoscopy. The degree of retraction required can frequently be lessened substantially. Traditionally, all microsurgi microsurgical cal approaches approaches can be conceptua conceptuallized as forming the shape of a cone, with the base on the surface of the head and the working space at the apex. With the use of angled endoscopes, this limitation can be overcome. At the tip of the cone of visualization and illumination available to the microscop microscope, e, 360 of additi additiona onall view view can be obtained. When working around the brain stem and cranial nerves, the corridor available to the micro microsco scope pe is often often narrow narrow,, becaus becausee extens extensive ive retr retrac acti tion on is freq freque uent ntly ly not not an opti option on.. The The endo endosc scop opee allo allows ws the the surg surgeo eon n to obta obtain in the the maximal access possible via the spaces naturally present in the extra-axial compartment. The The endo endosc scop opee has has allo allowe wed d a conc concep eptu tual al change in the approach to low-grade or ‘‘benign’’ tumors. A specific example of this point may be 

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Fig. 8. Preoper Preoperativ ativee ( A) and postoperative ( B) views of a tumor approached using a purely microsurgical approach. Note the location of residual tumor. This residuum would still be accessible with the endoscope.

illust illustrat rated ed by the case case of cranio craniopha pharyn ryngio gioma: ma: failure to achieve a complete resection ultimately proves disastrous for the patient. In the past, some surgeons surgeons have discouraged discouraged radical debulkin debulking g of  the hypothalamic portion of these tumors because of the the unac unacce cept ptab able le side side effec effects ts atte attend nded ed by dama damage ge to this this vita vitall stru struct ctur ure. e. In fact fact,, poor poor visual visualiza izatio tion n is what what limits limits adequa adequate te and safe safe removal of tumor. With the endoscope, the occult parts of the tumor can be removed under vision, making this part of the tumor as accessible as the directly visualized portion (Fig. ( Fig. 9). 9). Angled instruments allow access to the endoscopically visualized parts of the tumor. Because the prognosis for a number of tumors is a function of the adequacy of tumor removal, the use of the endoscope in this fashion to obtain the best removal possible and to document document that removal removal is highly highly recommend recommended. ed. Using Using this this ration rationale ale,, the author authorss encou encourage rage an aggressive approach to the management of lowgrade gra de tumors tumors,, such such as pilocy pilocytic tic astroc astrocyto ytomas mas,, pleom pleomorp orphic hic xantho xanthoast astroc rocyto ytomas mas,, and dysemdysembryopl bryoplast astic ic neuroe neuroepit pithel helial ial tumors tumors,, as well well as so-called ‘‘benign tumors,’’ such as craniopharyngiomas and meningiomas. Thus far, there are no studies documenting the superiority of the endoscopic approach to tumor removal. Some reports have begun to document its its use use in tran transs ssph phen enoi oida dall surg surger ery; y; surg surgeo eons ns famili familiar ar with with the improv improved ed view view offered offered in this this venue can easily imagine the same benefits applied within the rest of the cranial cavity. The endoscope is a powerful ally, but as is the case case with with all tools, tools, the surgeo surgeon n should should become become fully familiar with it before using it with patients. Practi Pra ctice ce is requir required ed to develo develop p the visuom visuomoto otorr skil skills ls nece necess ssar ary y to guid guidee the the tip tip in and and out out of  narrow narrow spaces spaces safely safely,, to watch watch the video image image while while still respecting respecting superficia superficiall structure structuress along along the shaft, shaft, and to work work with with other other instru instrumen ments ts

while while mainta maintaini ining ng good good visual visualiza izatio tion n with with the endoscop endoscope. e. Familiari Familiarizatio zation n with the endoscopi endoscopicc perspective and a review of the pertinent microsurgic surgical al anatom anatomy y are essent essential ial before before using using the endosc endoscop opee on patien patients. ts. Used Used proper properly, ly, it is an invaluable adjunct to traditional microsurgery. Technical notes 1. Guide the endoscope in and out of the field unde underr dire direct ct visi vision on.. The The most most dang danger erou ouss aspect of using the endoscope is the risk of  impact impacting ing struct structure uress while while introd introduci ucing ng the endo endosc scop ope. e. It is impo import rtan antt to guid guidee the the endoscope by viewing it along the length of  its barrel rather than by watching the image on the screen screen.. After After placin placing g the endosc endoscop opee into into the the work workin ing g area area,, it is esse essent ntia iall to cont contin inue ue to mind mind the the shaf shaft: t: if the the scop scopee is not fixed, small barely noticed movements at the tip can be the result of larger excursions at the back of the scope, which potentially can have have disast disastrou rouss conseq consequen uences ces.. An experi experi-enced assistant or a microscope with a headup endoscope display can help in this regard. 2. Use a fixed endoscope endoscope holder holder so that once the endoscope is in place, the surgeon can work with both hands. This allows the surgeon to use use more more comp comple lex x inst instru rume ment ntss and and also also prevents the endoscope from drifting against vital structures located superficially along the operative corridor.

Summary

Neuro-oncology, in all its aspects, provides an ideal ideal venue venue for the applic applicati ation on of endosc endoscopy opy.. The The main main obst obstacl aclee to its its use use has has been been neur neuroosurgeons’ lack of familiarity with the techniques

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Fig. 9. (A–C ) These MRI scans show a midbrain tumor in a 5-year-old girl. The tumor was removed through a small keyhole craniotomy and a transcallosal subchoroidal approach to the third ventricle. Once the microscope demonstrated what appeared to be complete removal, the endoscope was passed into the tumor cavity and more tumor was removed. (D–F ) These MRI scans show complete tumor removal. The pathologic finding was a benign xanthoma. There has been no recurrence after 4 years of follow-up.

and their advantages. As the neuro-oncologic surgeon uses the endoscope more, endoscopy will take its rightful place in the surgeon’s armamentarium. The advantages of improved visualization of intraventricular pathology, better management of tumor-related hydrocephalus, less morbid biopsies, and minimally invasive removal of intraventricular tumors are invaluable

adjuncts to traditional tumor management. Furthermore, endoscopy is the logical next step for surpassing the limitations of traditional microsurgery. Endoscopy is still in its infancy. Rigorous application of the technology is increasingly allowing us to provide our patients the most maximally effective and minimally invasive surgery possible.

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Fig. 9 (continued )

References [1] Wallner KR, Gonzales M, Sheline GE. Treatment of oligodendrogliomas with or without post-operative irradiation. J Neurosurg 1988;68:684–8. [2] Garcia DM, Fulling KH. Juvenile pilocytic astrocytomas of the cerebrum in adults. A distinctive neoplasm with favorable prognosis. J Neurosurg 1985;63:382–6. [3] Good CD, Wade AM, Hayward RD, Phipps KP, Michalski AJ, Harkness WF, et al. Surveillance neuroimaging in childhood intracranial ependymoma: how effective, how often, and for how long? J Neurosurg 2001;94(1):27–32. [4] Perneczky A, Fries G. Endoscope-assisted brain surgery:. part I—evolution, basic concept, and current technique. Neurosurgery 1998;42:219–25. [5] Teo C. Endoscopic-assisted tumor and neurovascular procedures. Clin Neurosurg 2000;46:515–25. [6] Perneczky A, Muller-Forell W, van Lindert E, Fries G. Keyhole concept in neurosurgery. Stuttgart: Thieme; 1999. [7] Ebinger F, Bruehl K, Gutjahr P. Early diffuse leptomeningeal primitive neuroectodermal tumors can escape detection by magnetic resonance imaging. Childs Nerv Syst 2000;16(7):398–401. [8] Oka K, Kin Y, Go Y, et al. Neuroendoscopic approach to tectal tumors: a consecutive series. J Neurosurg 1999;91(6):964–70. [9] Gaab MR, Schroeder HWS. Neuroendoscopic approach to intraventricular lesions. J Neurosurg 1998;88:496–505.

[10] Lewis AI, Crone KR, Taha J, et al. Surgical resection of third ventricle colloid cyst. Preliminary results comparing transcallosal microsurgery with endoscopy. J Neurosurg 1994;81:174–8. [11] Abdou MS, Cohen AR. Endoscopic treatment of  colloid cysts of the third ventricle: technical note and review of the literature. J Neurosurg 1998;89: 1062–8. [12] Rodziewicz GS, Smith MV, Hodge CJ. Endoscopic colloid cyst surgery. Neurosurgery 2000;46:655–  62. [13] El Khoury C, Brugieres P, Decq P, CossonStanescu R, Combes C, Ricolfi F, et al. Colloid cysts of the third ventricle: are MR imaging patterns predictive of difficulty with percutaneous treatment? AJNR Am J Neuroradiol 2000;21(3): 489–92. [14] Maeder PP, Holtas SL, Basibuyuk LN, Salford LG, Tapper UA, Brun A. Colloid cysts of the third ventricle: correlation of MR and CT findings with histology and chemical analysis. AJR Am J Roentgenol 1990;155(1):135–41. [15] Jimenez DF, editor. Intracranial endoscopic neurosurgery. Park Ridge, IL: American Association of  Neurological Surgeons; 1998. p. 132. [16] Abdullah J, Caemart J. Endoscopic management of  craniopharyngioma: a review of 3 cases. Minim Invasive Neurosurg 1995;38:79–84. [17] Cohen AR, Perneczky A, Rodziewciz GS, et al. Endoscope-assisted craniotomy: approach to the rostral brainstem. Neurosurgery 1995;36:1128–30.

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Index Note:  Page numbers of article titles are in  bold face  type.

A Aesculap neuroendoscopes, 23–26 Age factors, in third ventriculostomy outcome, 74–76 Aqueduct of Sylvius, occlusion of  CSF entrapment in, 84–85 third ventriculostomy for, 49–51, 73–74

Cerebellum anatomy of, 42–43 developmental anatomy of, 35 vermis of, agenesis of, 43 Cerebral aqueduct, anatomy of, 42 Cerebral arteries, injury of, in third ventriculostomy, 69–70

Arachnoid cysts,  9–17 clinical presentation of, 10 complications of, 16 diagnosis of, 10–11 frameless stereotactic systems for, 13–14 intraventricular, 10–11 laterally projecting, 13 locations of, 10 pathology and pathogenesis of, 9–10 shunting of, 15 suprasellar, clinical presentation of, 10 treatment of, 4, 11–16

Cerebrospinal fluid hydraulics of, 45–47 leakage of, in third ventriculostomy, 67

Arachnoid granulations, obstruction of, 48 Asystole, in third ventriculostomy, 69

Choroid plexus anatomy of, 37, 57–58 endoscopy of, 3

Auer Neuro-Endoscope, 23–24

Choroidal cysts, of lateral ventricle, 39–40

B Basilar artery, in third ventricle anatomy of, 41 injury of, in third ventriculostomy, 63, 69–70

Choroidal fissure, developmental anatomy of, 34

Biopsy, of tumor, endoscopic, 4, 100–101 Bleeding. See  Hemorrhage.

Channel neuroendoscope, 26 Chavantes-Zamorano Neuro-Endoscope, 23–24 Chiari II malformation, 43–44 fourth ventricle malformation in, 43–44 third ventricle malformation in, 42 third ventriculostomy contraindicated in, 48–49 Chip cameras, for endoscopy, 21

Clarus neuroendoscopes, 26 Coagulation, endoscopic equipment for, 27–28 Codman & Shurtleff neuroendoscopes, 26 Colloid cysts, endoscopic removal of, 4, 103–106

Bradycardia, in third ventriculostomy, 69

Communicating arteries, posterior, injury of, in third ventriculostomy, 69–70

Brain, tumors of. See  Tumor(s), brain.

Computed tomography, in arachnoid cysts, 11

Bugbee Wire, for hemostasis, 27

Cook & Codman, cauterization equipment of, 27–28

C Cameras, for endoscopy, 21 Catheter, peel-away, for endoscopy, 22 Cauterization, equipment for, 27–28

Copocephaly, 39 Corpus callosum agenesis of, 39, 42 developmental anatomy of, 34–35

1042-3680/04/$ - see front matter    2004 Elsevier Inc. All rights reserved. doi:10.1016/S1042-3680(03)00100-1

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Index / Neurosurg Clin N Am 15 (2004) 105–108

Craniopharyngioma, versus arachnoid cyst, 11–12 CSF. See  Cerebrospinal fluid. Cyst(s) arachnoid. See  Arachnoid cysts. choroidal, of lateral ventricle, 39–40 colloid, endoscopic removal of, 4, 103–106 Dandy Walker, 43 ependymal, of lateral ventricle, 39–40 solitary, drainage of, 88–89

scope holders, 29 syringomyeloscope, 27 video monitors, 21–22

F Fenestration of arachnoid cyst, 12–16 of multiloculated ventricles, 89–90 Fiberoptic endoscopes, 19–20, 25–26 Fogarty balloon, for endoscopy, 28

D Dandy classification, of hydrocephalus, 45

Foramen of Monro, anatomy of, 35–36

Dandy Walker cysts, 43

Fornix, anatomy of, 58

Decq Neuro-Endoscope, 23–24

Fourth ventricle anatomy of, 42–43 CSF entrapment in, 84–86, 89 malformations of, 43–44

Diverticula, of lateral ventricle, 39

E Electrocauterization, equipment for, 27–28 Embryology, of ventricular system, 33–36 Endocrine disorders, in third ventriculostomy, 64 Endoscopy equipment for,  19–31 for arachnoid cysts,  9–17 for cancer,  95–109 for hydrocephalus, with loculated ventricles, 83–93

history of, 1–7 principles of,  19–31 third ventriculostomy. See  Third ventriculostomy, endoscopic. ventricular anatomy for,  33–44 Ependymal cysts, of lateral ventricle, 39–40 Equipment, endoscopic,  19–31 cameras, 21 fiberoptic, 19–20, 25–26 for arachnoid cyst endoscopy, 12–15 for coagulation, 27–28 for CSF entrapment, 87–88 for shunt placement, 27 for third ventriculostomy, 60–61, 71 history of, 19–20 instruments, 28–29 lasers, 29, 62–63 light sources for, 20–21 optic angles in, 20 peel-away catheter, 22 rigid, 19, 22–26

Forceps, for endoscopy, 28

G Gaab Neuro-Endoscope, 23–24 H Headache in arachnoid cyst, 10 in slit ventricle syndrome, shunt removal in, third ventriculostomy for, 53–54 Hematoma, subdural, in third ventriculostomy, 68 Hemorrhage in arachnoid cyst endoscopy, 16 in third ventriculostomy, 63, 69–70 intraventricular, hydrocephalus in, third ventriculostomy for, 52 subarachnoid, hydrocephalus in, third ventriculostomy for, 52 ventricular, CSF entrapment in, 85–86 Hippocampus, developmental anatomy of, 33 Holoneural canal dilatation, in hydrocephalus, 85 Holoprosencephaly, 38 Hydranencephaly, 38–39 Hydrocephalus communicating, third ventriculostomy contraindicated in, 47–48 Dandy classification of, 45 double compartment, 85 etiology of, third ventriculostomy outcome and, 73, 78 hydromyelic, 85

Index / Neurosurg Clin N Am 15 (2004) 105–108

in aqueduct of Sylvius occlusion, 49–51 in arachnoid cyst, 10 in brain tumors, 51–52 in fourth ventricle malformations, 43–44 in infants, third ventriculostomy for, 52–53 in intracranial hemorrhage, third ventriculostomy for, 52 in lateral ventricle malformations, 38–40 in third ventricle malformations, 41–42 isolated compartments in,  83–93 multiloculated, 89–90 postinflammatory, 85–86 shunt-related, 83–85 solitary cysts in, 88–89 treatment of, 86–91 occlusive, in third ventriculostomy, 63 secondary, endoscopic treatment of, 96–99 third ventriculostomy for. See  Third ventriculostomy. Hypertension, intracranial, endoscopic treatment of, 3 Hypothalamus anatomy of, 40–41, 58 injury of, in third ventriculostomy, 64, 68

I Infant(s), hydrocephalus in, third ventriculostomy for, 52–53 Infections, CSF entrapment in, 85–86 Inflammation, CSF entrapment in, 85–86 Instruments, for endoscopy, 28–29 Intracranial hypertension, endoscopic treatment of, 3

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M Magnetic resonance imaging in aqueduct of Sylvius occlusion, 50 in arachnoid cysts, 10–11 in third ventriculostomy outcome assessment, 77, 79 Mamillary bodies, anatomy of, 40 Microsurgery, endoscopic-assisted, for tumors, 106–107 MINOP Neuroendoscopy System, 23–25 MurphyScope, 26 Myeloscopy, 4

N Neuroendoscopy. See  Endoscopy. NeuroNavigational endoscopes, 26 NeuroPen endoscope, 26 Neuroview endoscope, 25–26

O Occipital pole, anatomy of, 38 P Pneumocephalus, in third ventriculostomy, 67 Porencephaly, 39

R Rigid endoscopes, 19, 22–26

Intraventricular hemorrhage, hydrocephalus in, third ventriculostomy for, 52

S Schizencephaly, 38

L Lasers, for endoscopy, 29, 62–63

Seizures, in arachnoid cyst, 10

Light sources, for endoscopy, 20–21

Shunt CSF entrapment due to, 83–85 endoscopic equipment for, 27 existing, third ventriculostomy outcome with, 76 for arachnoid cyst, 15 removal of, third ventriculostomy for, 53–54

Loculations CSF entrapment in,  83–90 of fourth ventricle, 43 of lateral ventricle, 40

Slit ventricle syndrome entrapped CSF in, 83–85 shunt removal in, third ventriculostomy for, 53–54

Longstanding overt ventriculomegaly of the adult, 50–51

Subarachnoid hemorrhage, hydrocephalus in, third ventriculostomy for, 52

Lateral ventricle anatomy of, 36–38 CSF entrapment in, 84 malformations of, 38–40