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Endoscopic Approaches to Ventricular Tumors and Colloid Cysts
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Endoscopic Approaches to Ventricular Tumors and Colloid Cysts HELEN QUACH, SCOTT D. WAIT, VIJAY AGARWAL, CHARLES TEO
CLINICAL PEARLS • It is essential to be knowledgeable about the equipment and practice on a cadaver or to be under the guidance of an experienced neuroendoscopist. • Orientation and anatomy are everything. Knowledge of the anatomy will ensure that you know where you are, what you are looking at, and your orientation at all times. If you are not sure, abort the procedure. • Use the endoscope for its advantages, and do not fight its disadvantages. Increase the use of angled scopes, and increase the size of the visual field.
• Become comfortable with the endoscopic management of hydrocephalus (endoscopic third ventriculostomy) prior to using the endoscope for neuro-oncologic applications. • Endoscopic ventricular applications are not all or nothing. Some lesions are more safely dealt with from an open microsurgical approach. In these cases use an endoscope-assisted approach to your advantage.
Introduction The role for neuroendoscopy in the management of intraventricular tumors and colloid cysts is expanding. The endoscope provides an extended range of view not typically seen with microscopy, and it is also a useful adjunct to confirm the completeness of microscopic resection. On its own, it can be used to biopsy tumors, treat hydrocephalus, and definitively resect select tumors. Endoscopy remains a relatively new tool within the practice of many neurosurgical centers around the world, and it presents a significant learning curve to new practitioners. This chapter outlines how it may be used optimally in the context of colloid cyst and intraventricular tumor management and endoscope-assisted microsurgical procedures.
illumination, and instrumentation.3 It was not until technologic developments in lenses, electrical conduction, and fiber optics arose that a new generation of endoscopes could be created.4–6 Since the 1980s there has been a resurgent interest in neuroendoscopy, initially with regard to endoscopic third ventriculostomy procedures.7–11 As this has become increasingly popular, neurosurgeons have further explored the use of endoscopy for the treatment of more complicated pathologies,12–14 such as the biopsy and resection of ventricular tumors,15–18 the management of skull-base tumors,19,20 and even applications in spine surgery.21,22 The applications for neuroendoscopy have changed dramatically over the past century and will continue to evolve as technology advances and the next generation of pioneering surgeons is introduced to its use.
History
Instrumentation
The endoscope has long been used in neurosurgery. The first neuroendoscopic surgical procedure was performed in 1910 by Victor L’Espinasse, who used a cystoscope to treat hydrocephalus in children.1 Walter Dandy then performed the first endoscopic ventriculostomy in 1922.2 Though several pioneering neurosurgeons explored the use of the endoscope in ventricular surgery, its use was limited by difficulties in visualization,
The endoscope consists of a flexible or rigid tube with a lens system and a light source (typically fiber optic). The two main types of endoscopes are rigid lens scopes and flexible fiberscopes. Rigid lens scopes are fixed in length and geometry and come in a variety of viewing angles (0, 30, and 70 degrees to the long axis of the endoscope). They are optically superior and easier to orientate than flexible scopes. Flexible scopes are
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CHAPTER 45 Endoscopic Approaches to Ventricular Tumors and Colloid Cysts
composed of malleable fiber-optic cables, and thus steerable along three axes, and are able to be used on a curved trajectory. This functionality can be particularly useful in procedures such as pineal tumor biopsies along a curved path traversing the foramen of Monro to the posterior third ventricle, as seen in Fig. 45.1. Instrumentation is limited, as working channels are smaller and fewer than those with a rigid scope. Surgeons using the flexible fiberscope should also take extra care to not retract the scope while it is bent, as this can cause significant damage to vital surrounding structures. The two different types of scopes have their own unique uses and can be used in conjunction with one another. Some surgeons opt to use a rigid endoscope holding arm, which eliminates the need for an assistant to hold the scope and allows the surgeon to use both hands to operate. Although the holding arm can reduce tremor and accidental hand movements, small dynamic adjustments can be difficult to achieve. Frameless stereotactic neuronavigation is useful for the localization of periventricular cysts under an intact ependyma,
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as well as the selection of a trajectory and burr hole placement in colloid cyst removal.23 It increases the safety of neuroendoscopic procedures when the surgeon becomes disorientated or when anatomic landmarks are lacking.23,24 This may be particularly useful for patients without ventriculomegaly, which, when present, provides a naturally wider operative corridor. The resection of intraventricular cysts and tumors is currently hindered by limitations in instrumentation. Variable aspiration tissue resectors are emerging as a potential solution to decrease the time involved in the dissection and debulking of tumors. They have been reported to be safe and effective in reaching and removing tumors accessible only through narrow working corridors.25–28 One study on their use in neuroendoscopic resections of intraventricular tumors demonstrated feasibility for use with a variety of pathologies, though tumors larger than 20 mm were only subtotally resected.28 They should be used for nonvascular or devascularized tumors, as tumors cannot be devascularized by the device prior to debulking.29
Principles B
A
A
B • Figure 45.1 (A) Using a rigid endoscope requires two approaches to perform an endoscopic third ventriculostomy and biopsy a pineal tumor in most cases. (B) Using a flexible endoscope allows the same maneuvers through the traditional single burr hole approach used for endoscopic third ventriculostomy. (Adapted with permission from Barrow Neurological Institute; originally published in Winn HR, ed. Youmans Neurological Surgery. 6th ed. Philadelphia: WB Saunders; 2011.)
Endoscopic procedures are categorized as purely endoscopic neurosurgery, endoscope-assisted neurosurgery, or endoscopecontrolled microsurgery.30 Purely endoscopic techniques are performed through a burr hole, and instruments are introduced through the working channels in the sheath. It is considered a coaxial approach, as the components of the endoscopic system (lighting, camera, working channels, irrigant channels, and instruments) are in parallel and enclosed in a single sheath. Damage to surrounding brain from the retraction and introduction of instruments is minimized. Most intraventricular endoscopic procedures are coaxial.31 Extra axial approaches involve the introduction of instruments separate from the endoscope. Endoscope-assisted microsurgery and endoscope-controlled microsurgery are considered extra axial. In endoscope-assisted microsurgery, instruments are used in a bimanual technique under the microscope, and the endoscope assists visualization in, and around, corners. With endoscope-controlled microsurgery, the video image is used for guidance of microsurgical instruments rather than the microscope. In this scenario, curved instruments and suckers can be utilized to operate around corners. This results in a greater degree of technical difficulty due to peripheral distortion, disorientation from using an angled scope, and the proximity of the surgical field to the tip of the endoscope. However, mastering this skill can lead to more precise dissections and greater completeness of resection. For the management of selected colloid cysts and ventricular tumors, purely endoscopic techniques can be used safely and effectively.32–36 The scope is introduced through a burr hole under stereotactic guidance to the lateral ventricle. The resection of large or vascular intraventricular or periventricular tumors is enhanced by using both the microscope and the endoscope for visualization. The advantages and disadvantages to both endoscopy and microscopy are summarized in Table 45.1.
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TABLE 45.1 Advantages and Disadvantages of Using Microscopy and Endoscopy for Neurosurgical Procedures
Advantages
Disadvantages
Endoscopy
Greater visualization of areas not seen under microscopy Does not need focusing due to large depth of field Greater precision in viewing small detail. Image becomes brighter when the endoscope is closer to the object viewed Wide range of view Pure endoscopic techniques are more minimally invasive
Learning curve for instrumentation and orientation View easily obscured by hemorrhage Cannot see behind the endoscope Surgical manipulation limited to one hand Requires an assistant to hold endoscope, or endoscope holder View easily obscured by bleeding Limited instrumentation Pure endoscopic techniques should only be used for small tumors
Microscopy
Good visualization of objects in a straight path Good overview of surgical bed Allows for free bimanual technique
Difficulty seeing deeper structures and hidden corners—may require brain retraction Needs to be focused; field of view is limited as lens focuses on one depth Requires larger incision
Introduction to Colloid Cysts The management of colloid cysts has been a topic of contention in neurosurgical practice due to the risk of treatment and the relatively benign nature of these lesions. Colloid cysts are rare and benign lesions of neuroectodermal origin,37,38 arising from the roof of the third ventricle. They can cause obstruction of the foramen of Monro and cerebrospinal fluid outflow. This can result in a spectrum of symptoms from headaches to loss of consciousness and, on occasion, sudden death.18,39–41 Forniceal compression can also lead to memory loss.42
Management of Colloid Cysts Treatment options include the following: • Conservative management. The tumor and ventricles are observed for enlargement (“watch and wait”) • Placement of a ventriculoperitoneal shunt to treat hydrocephalus • Surgical resection of the lesion, which is the only definitive treatment Surgery is generally indicated in symptomatic patients or patients with ventriculomegaly, due to the risk of acute obstructive hydrocephalus and sudden death.34,43,44 Open transcallosal or transcortical microsurgical approaches have traditionally been the preferred methods of surgical resection, as they allow for easy bimanual access to the cyst and surrounding structures.45–47 However, a meta-analysis of 1278 patients with surgically treated colloid cysts has demonstrated that the open microsurgical approach carries significant risk, with an overall morbidity rate of 16.3%.48 In comparison, the endoscopic approach had a lower morbidity risk of 10.5%. This is the main advantage of the endoscopic approach; there was no statistically significant difference in mortality rate or shunt dependency, whereas open microsurgical resections generally resulted in higher gross total resection and lower recurrence. There have
been promising advances in endoscopic surgery, with the use of dual port and dual instrument techniques increasing the GTR rate in the resection of colloid cysts and intraventricular tumors.45,49–51 Traditional indications for surgery have been ventriculomegaly or symptomatic hydrocephalus. In general, enlarged ventricles are more easily accessed and provided a natural working area.52 However, we also recommend operating on select patients with symptoms of intermittent ventricular obstruction in the absence of hydrocephalus. We have been able to demonstrate good results in our series of 16 patients without ventriculoegaly.52 Our study compared 18 patients without hydrocephalus to 53 patients with hydrocephalus who underwent endoscopic removal of colloid cysts. Near total resection was achieved in all patients with no difference in morbidity or mortality. Stereotactic guidance is used to locate the ventricles and plan an appropriate trajectory. Care should be taken to avoid damage to the fornix, which lies in the superior and anterior borders of the foramen of Monro. Maintaining the size of the ventricles while operating can be facilitated through the use of a peel-away sheath, such that a natural vacuum is formed around the endoscope. The ventricles receive constant irrigation, and cerebrospinal fluid (CSF) is allowed to escape via a port. During the procedure, the patient’s vital signs are also continually monitored to avoid causing a Cushing response consisting of hypertension, bradycardia, and apnea.53 Further details of surgical techniques are outlined later in the chapter. A thorough history should also be taken in the workup of the patient prior to surgery. Colloid cysts are often found incidentally in patients whose underlying cause of headache may not be clear. Symptoms such as visual disturbance, loss of consciousness, positional headache, sensory disturbance, shortterm memory loss, urinary incontinence, dementia, or ataxia suggests intermittent ventricular obstruction. A neurologist should also review surgical candidates to rule out other causes of headache.
CHAPTER 45 Endoscopic Approaches to Ventricular Tumors and Colloid Cysts
Microsurgery is more appropriate for patients with cysts that are larger than 2 cm for whom resection may be prolonged under endoscopy, and patients with dense and proteinaceous cysts that are not easily aspirated. For patients with incidental colloid cysts that are not causing secondary hydrocephalus and are less than 1 cm in size, options are contentious. If the patient finds the knowledge of living with the cyst debilitating, then the choice to operate is dependent on informed consent and the surgeon’s experience. Conversely, if the patient is truly asymptomatic, has an acceptable level of anxiety about the risk of sudden death, appreciates the fact that the development of hydrocephalus may sometimes be occult and insidious, and is willing to have regular imaging and consultations, then observation alone is reasonable.
Planning Careful operative planning should be undertaken prior to commencing surgery: 1. Acquire preoperative MRI imaging for frameless stereotactic guidance. 2. Confirm the cyst’s size, location, and involvement of surrounding structures. 3. Ensure that all elements of the video chain and image guidance are in working order before starting the operation. 4. Place the patient’s head in three-point pin fixation, flexed at 45 degrees to the horizontal plane without lateral flexion or rotation. 5. Place a burr hole 8 cm from the nasion, 5 to 7 cm lateral to the midline in the nondominant hemisphere (Fig. 45.2): a. If the ventricle on the dominant side is significantly more dilated, consider an approach from the dominant side. b. The incision should be straight and just in front of or just behind the hairline. c. Use a coronal incision for cosmetic reasons should the incision need to be extended.
• Figure 45.2 The suggested approach for endoscopic resection of a colloid cyst is 8 cm posterior to the nasion and 5 to 7 cm right of the midline. The caudate head should be avoided during insertion of the sheath/endoscope.
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d. In bald males, where the incision cannot be hidden behind the hairline, consider an incision in the sagittal plane to reduce damage to sensory nerves. 6. Use frameless stereotaxy to confirm the trajectory.
Procedure 1. Create a burr hole large enough for easy maneuvering of the endoscope; 11 mm is usually sufficient. 2. Ensure that the endoscope and other instruments are in working order. 3. Tap into the lateral ventricle under stereotactic guidance, targeting the frontal horn: a. Avoid targeting the colloid cyst. This trajectory places the caudate head at risk of injury. b. Do not tap the ventricle with the endoscope or sheath. 4. Use a 0-degree scope to identify landmarks of the colloid cyst and foramen of Monro, such as the septal and thalamostriate veins and choroid plexus. In this initial step, the 0-degree scope is used for ease of orientation. 5. Change to a 30-degree scope. 6. Ensure the assistant is continuously irrigating to keep the ventricles open. Warmed lactated Ringer solution is preferred to normal saline. Large amounts of fluid are replaced in endoscopic ventricular surgery, and the use of saline has the potential to cause neural cell damage and postoperative electrolyte disturbance.54 7. The anesthesiologist should be monitoring for a Cushing response indicating raised intracranial pressure. If this occurs, allow for the egress of fluid. 8. Proceed with the removal of the cyst: a. If the cyst is small, i. Coagulate the overlying choroid plexus, avoiding the fornix. ii. Coagulate the contralateral choroid plexus if possible. iii. Using a grasper, remove the cyst as a whole. If this cannot be achieved, coagulate and open the cyst, aspirating the contents. iv. Prepare a pediatric endotracheal suction catheter cut at 45 degrees. If the cyst is mucinous, the cut end can be used to morselize the cyst and aspirate its contents. v. Remove using forceps if the content is too dense to aspirate. b. If the cyst is large, i. Attempt to decompress the cyst through the foramen or the ipsilateral thinned-out septum pellucidum that is stretched over the underlying cyst. Beware that the ipsilateral fornix is also stretched over the cyst, and every attempt should be made to minimize damage to this structure. ii. Coagulate the cyst. iii. Proceed to aspirate the contents. 9. Once the content is removed, then dissect the cyst wall from the attachment to the roof of the third ventricle: a. Use coagulation, blunt dissection, or sharp dissection as necessary.
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TABLE 45.2 Important Factors in the Surgical Management of Colloid Cysts
A. Patient and Tumor Factors Does the cyst cause radiologic hydrocephalus? Does the patient have symptoms consistent with intermittent ventricular obstruction? Have other causes of the symptoms been ruled out? Is the patient fully informed and in favor of surgical removal of the cyst? Is the patient informed of the risks and benefits of the procedure? (Risks include temporary memory loss, recurrence, and death.) Is the cyst small (<1.5 cm)? Does imaging suggest the cyst is mucinous rather than dense? Is the cyst adherent to the fornix or internal cerebral veins?
B. Surgeon Factors Is the surgeon experienced and confident with the use of the endoscope, stereotaxy, and other instrumentation involved? Have key structures been identified and avoided in the surgical trajectory? Is the surgeon in communication with the team? • Is the staff familiar with the equipment and setup? • Is the anesthetist monitoring the patient’s vital signs for the Cushing reflex that may be caused by increased intracranial pressure as a result of failure of egress of fluid? • Is the assistant continually irrigating the ventricles, especially when coagulating the choroid plexus? Is the port patent to allow egress of fluid? • Are the assistants mindful to avoid accidentally bumping the surgeon or endoscope? Has the surgeon checked that the equipment is working prior to starting the procedure? Are the marked incision and patient positions correct? Is the opening the right size? Is it too small to allow for comfortable movement of the instruments or larger than necessary? Are the surgeon and staff able to work ergonomically? Are the equipment, screens, and patient bed positioned to allow for this? Is the view of the endoscope maintained? • If there is bleeding, is the surgeon able to achieve hemostasis? • If hemostasis cannot be achieved through irrigation, consider using an instrument as a means of tamponade, coagulation of the vessel, or as a last resort draining the ventricles before finding the source of bleeding. Is the surgeon prepared to convert the procedure to an open one if necessary?
b. Consider that complete removal may not be possible if part of the wall remains adherent to the internal cerebral veins or the fornices, in which case either coagulate the remnants or consider conversion to an open approach if you believe it could be removed using standard microsurgical techniques. 10. If hemorrhage occurs during the procedure, there are several techniques to achieve hemostasis: a. It is preferable to first control bleeding by irrigation; in most cases this is sufficient to achieve hemostasis. b. If the source of bleeding can be seen, use the endoscope to tamponade the vessel. This method may be especially important to preserve large venous structures. c. The vessel can also be coagulated via monopolar or bipolar probes, but this is difficult. d. As a last resort, it is possible to drain CSF from the ventricles and coagulate in an air-filled environment or to convert to an open approach if bleeding cannot be controlled. Draining CSF from the ventricles by injecting air into them to minimize the risk that they will collapse is strongly recommended. 11. At the end of the procedure, endoscopic exploration of both the lateral and third ventricles is important to remove any blood clots that may have formed. Fill the ventricles
with fluid before plugging the cortical opening with Gelfoam. A burr hole cover in bald patients is optional. Close in a layered fashion. A checklist of important factors in the planning of surgery is outlined in Table 45.2.
Neurocysticercotic Cysts Neurocysticercosis (NCC) is a condition caused by the larvae of the tapeworm Taenia solium. It is the most common form of parasitic infection of the brain, and most often manifests as seizures.55,56 Cysts in the ventricular system can cause obstruction to CSF and hydrocephalus.57 In such cases, patients have traditionally been treated with ventriculoperitoneal shunting.58 However, the endoscopic excision of cysts has been shown to be safe and effective, and it is now an increasingly preferred method of treatment.59–64 CSF diversion can also be achieved during surgery by the creation of a third ventriculostomy, further reducing the need for shunt placement.65 As with other endoscopic procedures, the careful assessment of preoperating imaging prior to operating is recommended. Determine the CSF spaces to be explored and the safest trajectory to examine each one. The method can be performed via a single approach with a flexible endoscope or as many as
CHAPTER 45 Endoscopic Approaches to Ventricular Tumors and Colloid Cysts
required with a rigid endoscope. Ensure that a disposable plastic sheath is used to maintain the transcortical path, as sometimes the entire metal sheath needs to be removed with the grabbing forceps in order to maintain the integrity of the cyst wall. If the cyst wall is ruptured and contents spill into the ventricle, then postoperative steroids will alleviate some of the symptoms of sterile meningitis. When using the rigid endoscope, if the ventricle is not drained, firm irrigation can mobilize ipsilateral cysts into view that can be secured with a pair of forceps and removed.
Miscellaneous Cysts When operating on other cysts, such as arachnoid cysts, it is important to keep the same principles in mind. Planning and visualization are key. Working within the fluid-filled space of the ventricles makes the endoscope ideal for fenestration of these cysts. However, the anatomy can often be distorted and the arachnoid surface thick and opaque. Therefore it is beneficial to use stereotaxis to assist in visualizing any anatomic structures may be hidden behind an opaque membrane prior to fenestration. Avoid blunt perforation, as this can inadvertently cause damage to neurovascular structures behind the target.
Intraventricular Tumor Resection As with colloid cysts, intraventricular tumors most amenable to endoscopic removal are those with the following characteristics: • Small • Relatively avascular • Partially or completely cystic and • Located in enlarged ventricles
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Ventricles of at least normal size should be present for tumors to be safely biopsied or resected.66,67 The following tumors are usually avascular and are appropriately treated using pure endoscopic techniques: • Subependymomas • Ependymomas • Subependymal giant cell astrocytomas associated with tuberous sclerosis • Neurocytomas • Exophytic low-grade gliomas • Hypothalamic hamartomas Choroid plexus and pedunculated tumors may also be suitable if the blood supply can be easily accessed and coagulated.
Planning In planning endoscopic intraventricular tumor resection, it is particularly important to choose a trajectory that minimizes excessive “windshield wiping.” This can cause damage to surrounding structures, such as the fornix lying at the anterior border of the foramen of Monro. The right trajectory (Fig. 45.3) is one with the following characteristics: 1. Has some normal ventricle between the entry point and the targeted pathology, which allows for better visualization of normal structures and orientation 2. Allows access to the blood supply 3. Allows access to the point of attachment to the ventricular wall or choroid plexus; if the blood supply and points of attachments can be disconnected early, the tumor can often be removed en bloc quickly rather than piecemeal 4. Does not originate in or traverse eloquent structures 5. Allows management of associated hydrocephalus or trapped CSF spaces B
A
Approach trajectory A
Approach trajectory B • Figure 45.3 Choosing an appropriate approach that allows normal ventricle to be traversed prior to encountering the tumor gives a better view of the anatomy of the tumor and surrounding structures. It also allows identification and disconnection of the blood supply. (Adapted with permission from Barrow Neurological Institute; originally published in Winn HR, ed. Youmans Neurological Surgery. 6th ed. Philadelphia: WB Saunders; 2011.)
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Neuronavigation can be useful in planning the right trajectory. For tumors in the third ventricle, draw a line from the anterior-most border of the tumor to the foramen of Monro; this can be extrapolated to find an appropriate entry point and angle. This line helps minimize proximal movement of the scope. Another important factor that should be considered and controlled is the risk of becoming disoriented. This is a major cause of complications in endoscopic resections of intraventricular tumors. It is minimized through the following: • Choosing the right trajectory • Careful examination and orientation of the equipment and video image prior to entering the brain • Knowledge of normal ventricular anatomy • Being aware of the optical distortion caused by the endoscope • Use of frameless stereotactic guidance
Method 1. Tap the ventricle using a brain needle or ventriculostomy catheter. 2. Use frameless stereotactic navigation to place a peel-away sheath down the tract. 3. Use cup forceps to obtain a biopsy of the tumor prior to coagulation to maintain specimen quality. 4. Coagulate feeding vessels and the surface of the tumor. Disconnect the tumor from its pedicle. 5. Ensure the assistant is continuously irrigating with lactated Ringer solution to prevent overheating within the ventricles and to control any bleeding. 6. It is preferable to remove the tumor as a whole: a. If this is not possible, consider breaking up its contents and aspirating with a pediatric endotracheal suction catheter cut at 45 degrees or a stainless steel cannula. b. Avoid piecemeal resection and migration of tumor through the ventricles. c. Endoscopic ultrasonic aspirators are available and may help with large tumors. 7. Once the bulk of the tumor has been removed, inspect the ventricles for any remaining remnants or blood clots, especially in the foramen of Monro or aqueduct of Sylvius. 8. When there is a risk of obstruction, some surgeons may elect to place an external ventricular drain, though the authors would not recommend its routine use due to the risk of infection. 9. A septum pellucidotomy or third ventriculostomy may be appropriate to prevent postoperative hydrocephalus.
The most common complication of tumor biopsy is intraventricular hemorrhage. Other complications include tension pneumocephalus, obstructive hydrocephalus, and large vessel injury. Tension pneumocephalus can be avoided by refilling the ventricles with lactated Ringer solution. To prevent intraventricular hemorrhage, ensure adequate visualization before attempting to manipulate any structures. Several techniques to manage hemorrhage were outlined previously.
Endoscope-Assisted Microsurgery Where an open microsurgical approach is more appropriate for the removal of intraventricular or periventricular tumors, endoscopy can still play an important role by extending the field of visualization. Examples of cases where endoscopy can be used to assist microsurgical procedures include the following: • The removal of intraventricular portions of craniopharyngiomas • Cyst fenestration and collapse prior to craniotomy to remove the solid component of a tumor Cystic and large tumors are particularly suited to this method, as the initial decompression of the lesion under microscopy creates a working space in which to manipulate the endoscope.69 This reduces the need for brain retraction and minimizes parenchymal damage. Diagnostic ventriculoscopy uses the endoscope for inspection purposes. A 30-degree scope is best suited in these cases, as it provides a wide field of view and minimizes the need for brain retraction. Ventriculoscopy can be used to perform various functions: • Identify ependymal tumor deposits not seen on MRI • Determine the patency of the aqueduct or other CSF pathways • Check for residual blood clots or tumor remnants
Process 1. Have the endoscopic equipment ready in the room for all patients. 2. Nursing staff should set up the endoscopic equipment while the surgeon achieves hemostasis under microscopy: achieving hemostasis prior to using the endoscope is especially important as its view can be easily obscured by bleeding. 3. Switch from microscope to endoscope: a. Introduce the endoscope under microscopic guidance. b. Elevate the microscope away from the patient so the endoscope may be reintroduced easily.
Biopsy of Intraventricular Tumors
Conclusion and Future Directions
Periventricular CNS lymphomas and “nonoperative” gliomas may be appropriately biopsied by the use of endoscopy. The difficulty of locating the tumor may be alleviated with the use of image guidance. The 5-ALA has also been reported to be a useful tool in identifying gliomas through an intact ependyma.68
The endoscope has truly revolutionized the way neurosurgeons approach brain tumors in general and intraventricular tumors in particular. The natural corridor that the ventricles provide makes endoscopy particularly applicable. Purely intraventricular tumors, such as colloid cysts and other avascular lesions, may be totally removed through a burr hole and a single
CHAPTER 45 Endoscopic Approaches to Ventricular Tumors and Colloid Cysts
atraumatic cortical corridor with excellent visualization, hemostasis, and angled inspection of the tumor bed to ensure the completeness of the resection. Endoscope-assisted microsurgery has been equally beneficial by enabling the surgeon to look around corners, remove tumors from multiple compartments without multiple entry points, and identify neurovascular structures early to prevent irreversible damage. Endoscopy in neurosurgery is a dynamic practice; advances are constantly occurring. Just as angled endoscopes provided superior access to previously obstructed views, curved and adjustable instruments are now allowing treatment of previously unseen pathologies. Combination instruments, such as the adjustable suction-bipolar, have allowed solo neurosurgeons to handle both the endoscope and the instruments simultaneously. In the future, advances facilitating endoscopic sharp dissection and hemostasis are welcomed. Also needed are sharper imaging modalities for both flexible and rod-lens endoscopes and better integration with stereotactic guidance systems. Major advances in both endoscope and instrument development will be aided by earlier integration of endoscopic techniques into training programs. As more and more neu-
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rosurgeons incorporate these techniques and approaches into their practices, the need for more precise viewing and accurate instrumentation will grow. Just as endoscopy has become a mainstay in other specialties, such as general surgery and orthopedic surgery, it will soon be a necessary skill for all neurosurgeons in order to offer their patients the best possible management options for intraventricular lesions. It is our hope that commercial vendors, engineers, and neurosurgeons can collaborate to continue advancing this field and to keep up with the steady and growing demand from current and future practitioners.
Selected Key References Abdou MS, Cohen AR. Endoscopic treatment of colloid cysts of the third ventricle. Technical note and review of the literature. J Neurosurg. 1998;89(6):1062-1068. Sheikh AB, Mendelson ZS, Liu JK. Endoscopic versus microsurgical resection of colloid cysts: a systematic review and meta-analysis of 1,278 patients. World Neurosurg. 2014;82(6):1187-1197. Please go to ExpertConsult.com to view the complete list of references.
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References 1. Grant JA. Victor Darwin Lespinasse: a biographical sketch. Neurosurgery. 1996;39(6):1232-1233. 2. Dandy W. An operative procedure for hydrocephalus. Bull Johns Hopkins Hosp. 1922;33:189-190. 3. Dandy W. Surgery of the Brain. Hagerstown, MD: W.F. Prior Co.; 1945. 4. Anderson WS. Neuroendoscopic optics. In: •• JEC, Jallo GI, Bognar L, eds. Neuroendoscopy of the Central Nervous System. Plural, San Diego: 2008:5-12. 5. Abbott R. History of neuroendoscopy. Neurosurg Clin N Am. 2004;15(1):1-7. 6. Di Rocco C, et al. Prediction of outcome of endoscopic third ventriculostomy. World Neurosurg. 2013;80(5):509-511. 7. Vries JK. An endoscopic technique for third ventriculostomy. Surg Neurol. 1978;9(3):165-168. 8. Jones RF, Stening WA, Brydon M. Endoscopic third ventriculostomy. Neurosurgery. 1990;26(1):86-91, discussion 91-2. 9. Jones RF, et al. Third ventriculostomy for hydrocephalus associated with spinal dysraphism: indications and contraindications. Eur J Pediatr Surg. 1996;6(suppl 1):5-6. 10. Teo C. Third Ventriculostomy in the Treatment of Hydrocephalus: Experience with More than 120 Cases. In: Hellwig D, Bauer BL, eds. Minimally Invasive Techniques for Neurosurgery: Current Status and Future Perspectives. Berlin, Heidelberg: Springer Berlin Heidelberg; 1998:73-76. 11. Teo C, Jones R. Management of hydrocephalus by endoscopic third ventriculostomy in patients with myelomeningocele. Pediatr Neurosurg. 1996;25(2):57-63, discussion 63. 12. Hamada H, et al. Neuroendoscopic septostomy for isolated lateral ventricle. Neurol Med Chir (Tokyo). 2003;43(12):582-587, discussion 588. 13. Oi S, Abbott R. Loculated ventricles and isolated compartments in hydrocephalus: their pathophysiology and the efficacy of neuroendoscopic surgery. Neurosurg Clin N Am. 2004;15(1):77-87. 14. Di Rocco F, Yoshino M, Oi S. Neuroendoscopic transventricular ventriculocystostomy in treatment for intracranial cysts. J Neurosurg. 2005;103(1 suppl):54-60. 15. Fukushima T. Endoscopic biopsy of intraventricular tumors with the use of a ventriculofiberscope. Neurosurgery. 1978;2(2):110-113. 16. Souweidane MM. Endoscopic surgery for intraventricular brain tumors in patients without hydrocephalus. Neurosurgery. 2005;57(4 suppl):312-318, discussion 312-8. 17. Souweidane MM, Luther N. Endoscopic resection of solid intraventricular brain tumors. J Neurosurg. 2006;105(2):271-278. 18. Abdou MS, Cohen AR. Endoscopic treatment of colloid cysts of the third ventricle. Technical note and review of the literature. J Neurosurg. 1998;89(6):1062-1068. 19. de Divitiis E, Cappabianca P, de Divitiis O. The “schola medica salernitana”: the forerunner of the modern university medical schools. Neurosurgery. 2004;55(4):722-744, discussion 744-5. 20. Carrau RL, Jho HD, Ko Y. Transnasal-transsphenoidal endoscopic surgery of the pituitary gland. Laryngoscope. 1996;106(7): 914-918. 21. Khoo LT, Fessler RG. Microendoscopic decompressive laminotomy for the treatment of lumbar stenosis. Neurosurgery. 2002;51(5 suppl):S146-S154. 22. Dickman CA, Karahalios DG. Thoracoscopic spinal surgery. Clin Neurosurg. 1996;43:392-422. 23. Rohde V, et al. The role of neuronavigation in intracranial endoscopic procedures. Neurosurg Rev. 2012;35(3):351-358.
24. Longatti P, et al. Endoscopic opening of the foramen of Magendie using transaqueductal navigation for membrane obstruction of the fourth ventricle outlets. Technical note. J Neurosurg. 2006;105(6): 924-927. 25. Garcia-Navarro V, et al. Use of a side-cutting aspiration device for resection of tumors during endoscopic endonasal approaches. Neurosurg Focus. 2011;30(4):E13. 26. McLaughlin N, et al. Side-cutting aspiration device for endoscopic and microscopic tumor removal. J Neurol Surg B Skull Base. 2012;73(1):11-20. 27. Dlouhy BJ, Dahdaleh NS, Greenlee JD. Emerging technology in intracranial neuroendoscopy: application of the NICO Myriad. Neurosurg Focus. 2011;30(4):E6. 28. Nduom EK, et al. Neuroendoscopic Resection of Intraventricular Tumors and Cysts through a Working Channel with a Variable Aspiration Tissue Resector: A Feasibility and Safety Study. Minim Invasive Surg. 2013;2013:471805. 29. Mohanty A. The current role of endoscopes in intracranial tumor surgery. J Neurosci Rural Pract. 2013;4(1):3-5. 30. Hopf NJ, Perneczky A. Endoscopic neurosurgery and endoscopeassisted microneurosurgery for the treatment of intracranial cysts. Neurosurgery. 1998;43(6):1330-1336, discussion 1336-7. 31. Nakaji P, Teo C. Endoscopic approaches to brain tumors. In: Youmas Neurological Surgery. 2011:1300-1308. 32. Levine NB, Miller MN, Crone KR. Endoscopic resection of colloid cysts: indications, technique, and results during a 13-year period. Minim Invasive Neurosurg. 2007;50(6):313-317. 33. Greenlee JD, et al. Purely endoscopic resection of colloid cysts. Neurosurgery. 2008;62(3 suppl 1):51-55, discussion 55-6. 34. Lewis AI, et al. Surgical resection of third ventricle colloid cysts. Preliminary results comparing transcallosal microsurgery with endoscopy. J Neurosurg. 1994;81(2):174-178. 35. Horn EM, et al. Treatment options for third ventricular colloid cysts: comparison of open microsurgical versus endoscopic resection. Neurosurgery. 2007;60(4):613-618, discussion 618-20. 36. Schroeder HW, Gaab MR. Endoscopic resection of colloid cysts. Neurosurgery. 2002;51(6):1441-1444, discussion 1444-5. 37. Stachura K, et al. Colloid cysts of the third ventricle. Endoscopic and open microsurgical management. Neurol Neurochir Pol. 2009;43(3):251-257. 38. Turillazzi E, et al. Colloid cyst of the third ventricle, hypothalamus, and heart: a dangerous link for sudden death. Diagn Pathol. 2012;7:144. 39. Desai KI, et al. Surgical management of colloid cyst of the third ventricle–a study of 105 cases. Surg Neurol. 2002;57(5):295-302, discussion 302-4. 40. Hellwig D, et al. Neuroendoscopic treatment for colloid cysts of the third ventricle: the experience of a decade. Neurosurgery. 2003;52(3):525-533, discussion 532-3. 41. Pollock BE, Huston J 3rd. Natural history of asymptomatic colloid cysts of the third ventricle. J Neurosurg. 1999;91(3):364369. 42. Aggleton JP, et al. Differential cognitive effects of colloid cysts in the third ventricle that spare or compromise the fornix. Brain. 2000;123(4):800-815. 43. Macdonald RL, et al. Colloid cysts in children. Pediatr Neurosurg. 1994;20(3):169-177. 44. Mathiesen T, et al. Third ventricle colloid cysts: a consecutive 12-year series. J Neurosurg. 1997;86(1):5-12. 45. Bergsneider M. Complete microsurgical resection of colloid cysts with a dual-port endoscopic technique. Neurosurgery. 2007;60(2 suppl 1):ONS33-ONS42, discussion ONS42-3.
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46. Hernesniemi J, Leivo S. Management outcome in third ventricular colloid cysts in a defined population: A series of 40 patients treated mainly by transcallosal microsurgery. Surg Neurol. 1996;45(1): 2-11. 47. Sampath R, Vannemreddy P, Nanda A. Microsurgical excision of colloid cyst with favorable cognitive outcomes and short operative time and hospital stay: operative techniques and analyses of outcomes with review of previous studies. Neurosurgery. 2010;66(2):368-374, discussion 374-5. 48. Sheikh AB, Mendelson ZS, Liu JK. Endoscopic versus microsurgical resection of colloid cysts: a systematic review and meta-analysis of 1,278 patients. World Neurosurg. 2014;82(6):1187-1197. 49. Harris AE, et al. Microsurgical removal of intraventricular lesions using endoscopic visualization and stereotactic guidance. Neurosurgery. 2005;56(1 suppl):125-132, discussion 125-32. 50. Wilson DA, et al. Endoscopic resection of colloid cysts: use of a dual-instrument technique and an anterolateral approach. World Neurosurg. 2013;80(5):576-583. 51. Engh JA, et al. Stereotactically guided endoscopic port surgery for intraventricular tumor and colloid cyst resection. Neurosurgery. 2010;67(3 supplOperative):ons198-ons204, discussion ons204-5. 52. Wait SD, et al. Endoscopic colloid cyst resection in the absence of ventriculomegaly. Neurosurgery. 2013;73(1 supplOperative):ons39ons46, ons46-7. 53. Agrawal A, et al. Bradycardia in neurosurgery. Clin Neurol Neurosurg. 2008;110(4):321-327. 54. Kazim SF, Enam SA, Shamim MS. Possible detrimental effects of neurosurgical irrigation fluids on neural tissue: An evidence based analysis of various irrigants used in contemporary neurosurgical practice. Int J Surg. 2010;8(8):586-590. 55. Garcia HH, et al. Taenia solium cysticercosis. Lancet. 2003; 362(9383):547-556. 56. Sotelo J, Del Brutto OH. Review of neurocysticercosis. Neurosurg Focus. 2002;12(6):e1.
57. Rajshekhar V. Surgical management of neurocysticercosis. Int J Surg. 2010;8(2):100-104. 58. Cuetter AC, et al. Neurocysticercosis: focus on intraventricular disease. Clin Infect Dis. 1997;24(2):157-164. 59. Zymberg ST, et al. Endoscopic approach to fourth ventricle cysticercosis. Arq Neuropsiquiatr. 2003;61(2A):204-207. 60. Anandh B, et al. Endoscopic approach to intraventricular cysticercal lesions. Minim Invasive Neurosurg. 2001;44(4):194-196. 61. Bergsneider M, et al. Endoscopic management of cysticercal cysts within the lateral and third ventricles. J Neurosurg. 2000;92(1):14-23. 62. Husain M, et al. Neuro-endoscopic management of intraventricular neurocysticercosis (NCC). Acta Neurochir (Wien). 2007;149(4): 341-346. 63. Husain M, et al. Endoscopic transaqueductal removal of fourth ventricular neurocysticercosis with an angiographic catheter. Neurosurgery. 2007;60(4 suppl 2):249-253, discussion 254. 64. Bergsneider M. Endoscopic removal of cysticercal cysts within the fourth ventricle: technique and results. Neurosurg Focus. 1999; 6(4):e8. 65. Goel RK, et al. Endoscopic management of intraventricular neurocysticercosis. J Clin Neurosci. 2008;15(10):1096-1101. 66. Yamamoto M, et al. Flexible neuroendoscopy for percutaneous treatment of intraventricular lesions in the absence of hydrocephalus. Minim Invasive Neurosurg. 1997;40(4):139-143. 67. Souweidane MM. Endoscopic surgery for intraventricular brain tumors in patients without hydrocephalus. Neurosurgery. 2008;62(6 suppl 3):1042-1048. 68. Tamura Y, et al. Endoscopic identification and biopsy sampling of an intraventricular malignant glioma using a 5-aminolevulinic acidinduced protoporphyrin IX fluorescence imaging system. Technical note. J Neurosurg. 2007;106(3):507-510. 69. Garrett M, Spetzler RF. Endoscopic microsurgery. In: Daroff RB, Aminoff MJ, eds. Encyclopedia of the Neurological Sciences. St. Louis: Elsevier.; 2014:50-52.
45
Endoscopic Approaches to Ventricular Tumors and Colloid Cysts HELEN QUACH, SCOTT D. WAIT, VIJAY AGARWAL, CHARLES TEO
CLINICAL PEARLS • It is essential to be knowledgeable about the equipment and practice on a cadaver or to be under the guidance of an experienced neuroendoscopist. • Orientation and anatomy are everything. Knowledge of the anatomy will ensure that you know where you are, what you are looking at, and your orientation at all times. If you are not sure, abort the procedure. • Use the endoscope for its advantages, and do not fight its disadvantages. Increase the use of angled scopes, and increase the size of the visual field.
• Become comfortable with the endoscopic management of hydrocephalus (endoscopic third ventriculostomy) prior to using the endoscope for neuro-oncologic applications. • Endoscopic ventricular applications are not all or nothing. Some lesions are more safely dealt with from an open microsurgical approach. In these cases use an endoscope-assisted approach to your advantage.
Introduction The role for neuroendoscopy in the management of intraventricular tumors and colloid cysts is expanding. The endoscope provides an extended range of view not typically seen with microscopy, and it is also a useful adjunct to confirm the completeness of microscopic resection. On its own, it can be used to biopsy tumors, treat hydrocephalus, and definitively resect select tumors. Endoscopy remains a relatively new tool within the practice of many neurosurgical centers around the world, and it presents a significant learning curve to new practitioners. This chapter outlines how it may be used optimally in the context of colloid cyst and intraventricular tumor management and endoscope-assisted microsurgical procedures.
illumination, and instrumentation.3 It was not until technologic developments in lenses, electrical conduction, and fiber optics arose that a new generation of endoscopes could be created.4–6 Since the 1980s there has been a resurgent interest in neuroendoscopy, initially with regard to endoscopic third ventriculostomy procedures.7–11 As this has become increasingly popular, neurosurgeons have further explored the use of endoscopy for the treatment of more complicated pathologies,12–14 such as the biopsy and resection of ventricular tumors,15–18 the management of skull-base tumors,19,20 and even applications in spine surgery.21,22 The applications for neuroendoscopy have changed dramatically over the past century and will continue to evolve as technology advances and the next generation of pioneering surgeons is introduced to its use.
History
Instrumentation
The endoscope has long been used in neurosurgery. The first neuroendoscopic surgical procedure was performed in 1910 by Victor L’Espinasse, who used a cystoscope to treat hydrocephalus in children.1 Walter Dandy then performed the first endoscopic ventriculostomy in 1922.2 Though several pioneering neurosurgeons explored the use of the endoscope in ventricular surgery, its use was limited by difficulties in visualization,
The endoscope consists of a flexible or rigid tube with a lens system and a light source (typically fiber optic). The two main types of endoscopes are rigid lens scopes and flexible fiberscopes. Rigid lens scopes are fixed in length and geometry and come in a variety of viewing angles (0, 30, and 70 degrees to the long axis of the endoscope). They are optically superior and easier to orientate than flexible scopes. Flexible scopes are
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CHAPTER 45 Endoscopic Approaches to Ventricular Tumors and Colloid Cysts
composed of malleable fiber-optic cables, and thus steerable along three axes, and are able to be used on a curved trajectory. This functionality can be particularly useful in procedures such as pineal tumor biopsies along a curved path traversing the foramen of Monro to the posterior third ventricle, as seen in Fig. 45.1. Instrumentation is limited, as working channels are smaller and fewer than those with a rigid scope. Surgeons using the flexible fiberscope should also take extra care to not retract the scope while it is bent, as this can cause significant damage to vital surrounding structures. The two different types of scopes have their own unique uses and can be used in conjunction with one another. Some surgeons opt to use a rigid endoscope holding arm, which eliminates the need for an assistant to hold the scope and allows the surgeon to use both hands to operate. Although the holding arm can reduce tremor and accidental hand movements, small dynamic adjustments can be difficult to achieve. Frameless stereotactic neuronavigation is useful for the localization of periventricular cysts under an intact ependyma,
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as well as the selection of a trajectory and burr hole placement in colloid cyst removal.23 It increases the safety of neuroendoscopic procedures when the surgeon becomes disorientated or when anatomic landmarks are lacking.23,24 This may be particularly useful for patients without ventriculomegaly, which, when present, provides a naturally wider operative corridor. The resection of intraventricular cysts and tumors is currently hindered by limitations in instrumentation. Variable aspiration tissue resectors are emerging as a potential solution to decrease the time involved in the dissection and debulking of tumors. They have been reported to be safe and effective in reaching and removing tumors accessible only through narrow working corridors.25–28 One study on their use in neuroendoscopic resections of intraventricular tumors demonstrated feasibility for use with a variety of pathologies, though tumors larger than 20 mm were only subtotally resected.28 They should be used for nonvascular or devascularized tumors, as tumors cannot be devascularized by the device prior to debulking.29
Principles B
A
A
B • Figure 45.1 (A) Using a rigid endoscope requires two approaches to perform an endoscopic third ventriculostomy and biopsy a pineal tumor in most cases. (B) Using a flexible endoscope allows the same maneuvers through the traditional single burr hole approach used for endoscopic third ventriculostomy. (Adapted with permission from Barrow Neurological Institute; originally published in Winn HR, ed. Youmans Neurological Surgery. 6th ed. Philadelphia: WB Saunders; 2011.)
Endoscopic procedures are categorized as purely endoscopic neurosurgery, endoscope-assisted neurosurgery, or endoscopecontrolled microsurgery.30 Purely endoscopic techniques are performed through a burr hole, and instruments are introduced through the working channels in the sheath. It is considered a coaxial approach, as the components of the endoscopic system (lighting, camera, working channels, irrigant channels, and instruments) are in parallel and enclosed in a single sheath. Damage to surrounding brain from the retraction and introduction of instruments is minimized. Most intraventricular endoscopic procedures are coaxial.31 Extra axial approaches involve the introduction of instruments separate from the endoscope. Endoscope-assisted microsurgery and endoscope-controlled microsurgery are considered extra axial. In endoscope-assisted microsurgery, instruments are used in a bimanual technique under the microscope, and the endoscope assists visualization in, and around, corners. With endoscope-controlled microsurgery, the video image is used for guidance of microsurgical instruments rather than the microscope. In this scenario, curved instruments and suckers can be utilized to operate around corners. This results in a greater degree of technical difficulty due to peripheral distortion, disorientation from using an angled scope, and the proximity of the surgical field to the tip of the endoscope. However, mastering this skill can lead to more precise dissections and greater completeness of resection. For the management of selected colloid cysts and ventricular tumors, purely endoscopic techniques can be used safely and effectively.32–36 The scope is introduced through a burr hole under stereotactic guidance to the lateral ventricle. The resection of large or vascular intraventricular or periventricular tumors is enhanced by using both the microscope and the endoscope for visualization. The advantages and disadvantages to both endoscopy and microscopy are summarized in Table 45.1.
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TABLE 45.1 Advantages and Disadvantages of Using Microscopy and Endoscopy for Neurosurgical Procedures
Advantages
Disadvantages
Endoscopy
Greater visualization of areas not seen under microscopy Does not need focusing due to large depth of field Greater precision in viewing small detail. Image becomes brighter when the endoscope is closer to the object viewed Wide range of view Pure endoscopic techniques are more minimally invasive
Learning curve for instrumentation and orientation View easily obscured by hemorrhage Cannot see behind the endoscope Surgical manipulation limited to one hand Requires an assistant to hold endoscope, or endoscope holder View easily obscured by bleeding Limited instrumentation Pure endoscopic techniques should only be used for small tumors
Microscopy
Good visualization of objects in a straight path Good overview of surgical bed Allows for free bimanual technique
Difficulty seeing deeper structures and hidden corners—may require brain retraction Needs to be focused; field of view is limited as lens focuses on one depth Requires larger incision
Introduction to Colloid Cysts The management of colloid cysts has been a topic of contention in neurosurgical practice due to the risk of treatment and the relatively benign nature of these lesions. Colloid cysts are rare and benign lesions of neuroectodermal origin,37,38 arising from the roof of the third ventricle. They can cause obstruction of the foramen of Monro and cerebrospinal fluid outflow. This can result in a spectrum of symptoms from headaches to loss of consciousness and, on occasion, sudden death.18,39–41 Forniceal compression can also lead to memory loss.42
Management of Colloid Cysts Treatment options include the following: • Conservative management. The tumor and ventricles are observed for enlargement (“watch and wait”) • Placement of a ventriculoperitoneal shunt to treat hydrocephalus • Surgical resection of the lesion, which is the only definitive treatment Surgery is generally indicated in symptomatic patients or patients with ventriculomegaly, due to the risk of acute obstructive hydrocephalus and sudden death.34,43,44 Open transcallosal or transcortical microsurgical approaches have traditionally been the preferred methods of surgical resection, as they allow for easy bimanual access to the cyst and surrounding structures.45–47 However, a meta-analysis of 1278 patients with surgically treated colloid cysts has demonstrated that the open microsurgical approach carries significant risk, with an overall morbidity rate of 16.3%.48 In comparison, the endoscopic approach had a lower morbidity risk of 10.5%. This is the main advantage of the endoscopic approach; there was no statistically significant difference in mortality rate or shunt dependency, whereas open microsurgical resections generally resulted in higher gross total resection and lower recurrence. There have
been promising advances in endoscopic surgery, with the use of dual port and dual instrument techniques increasing the GTR rate in the resection of colloid cysts and intraventricular tumors.45,49–51 Traditional indications for surgery have been ventriculomegaly or symptomatic hydrocephalus. In general, enlarged ventricles are more easily accessed and provided a natural working area.52 However, we also recommend operating on select patients with symptoms of intermittent ventricular obstruction in the absence of hydrocephalus. We have been able to demonstrate good results in our series of 16 patients without ventriculoegaly.52 Our study compared 18 patients without hydrocephalus to 53 patients with hydrocephalus who underwent endoscopic removal of colloid cysts. Near total resection was achieved in all patients with no difference in morbidity or mortality. Stereotactic guidance is used to locate the ventricles and plan an appropriate trajectory. Care should be taken to avoid damage to the fornix, which lies in the superior and anterior borders of the foramen of Monro. Maintaining the size of the ventricles while operating can be facilitated through the use of a peel-away sheath, such that a natural vacuum is formed around the endoscope. The ventricles receive constant irrigation, and cerebrospinal fluid (CSF) is allowed to escape via a port. During the procedure, the patient’s vital signs are also continually monitored to avoid causing a Cushing response consisting of hypertension, bradycardia, and apnea.53 Further details of surgical techniques are outlined later in the chapter. A thorough history should also be taken in the workup of the patient prior to surgery. Colloid cysts are often found incidentally in patients whose underlying cause of headache may not be clear. Symptoms such as visual disturbance, loss of consciousness, positional headache, sensory disturbance, shortterm memory loss, urinary incontinence, dementia, or ataxia suggests intermittent ventricular obstruction. A neurologist should also review surgical candidates to rule out other causes of headache.
CHAPTER 45 Endoscopic Approaches to Ventricular Tumors and Colloid Cysts
Microsurgery is more appropriate for patients with cysts that are larger than 2 cm for whom resection may be prolonged under endoscopy, and patients with dense and proteinaceous cysts that are not easily aspirated. For patients with incidental colloid cysts that are not causing secondary hydrocephalus and are less than 1 cm in size, options are contentious. If the patient finds the knowledge of living with the cyst debilitating, then the choice to operate is dependent on informed consent and the surgeon’s experience. Conversely, if the patient is truly asymptomatic, has an acceptable level of anxiety about the risk of sudden death, appreciates the fact that the development of hydrocephalus may sometimes be occult and insidious, and is willing to have regular imaging and consultations, then observation alone is reasonable.
Planning Careful operative planning should be undertaken prior to commencing surgery: 1. Acquire preoperative MRI imaging for frameless stereotactic guidance. 2. Confirm the cyst’s size, location, and involvement of surrounding structures. 3. Ensure that all elements of the video chain and image guidance are in working order before starting the operation. 4. Place the patient’s head in three-point pin fixation, flexed at 45 degrees to the horizontal plane without lateral flexion or rotation. 5. Place a burr hole 8 cm from the nasion, 5 to 7 cm lateral to the midline in the nondominant hemisphere (Fig. 45.2): a. If the ventricle on the dominant side is significantly more dilated, consider an approach from the dominant side. b. The incision should be straight and just in front of or just behind the hairline. c. Use a coronal incision for cosmetic reasons should the incision need to be extended.
• Figure 45.2 The suggested approach for endoscopic resection of a colloid cyst is 8 cm posterior to the nasion and 5 to 7 cm right of the midline. The caudate head should be avoided during insertion of the sheath/endoscope.
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d. In bald males, where the incision cannot be hidden behind the hairline, consider an incision in the sagittal plane to reduce damage to sensory nerves. 6. Use frameless stereotaxy to confirm the trajectory.
Procedure 1. Create a burr hole large enough for easy maneuvering of the endoscope; 11 mm is usually sufficient. 2. Ensure that the endoscope and other instruments are in working order. 3. Tap into the lateral ventricle under stereotactic guidance, targeting the frontal horn: a. Avoid targeting the colloid cyst. This trajectory places the caudate head at risk of injury. b. Do not tap the ventricle with the endoscope or sheath. 4. Use a 0-degree scope to identify landmarks of the colloid cyst and foramen of Monro, such as the septal and thalamostriate veins and choroid plexus. In this initial step, the 0-degree scope is used for ease of orientation. 5. Change to a 30-degree scope. 6. Ensure the assistant is continuously irrigating to keep the ventricles open. Warmed lactated Ringer solution is preferred to normal saline. Large amounts of fluid are replaced in endoscopic ventricular surgery, and the use of saline has the potential to cause neural cell damage and postoperative electrolyte disturbance.54 7. The anesthesiologist should be monitoring for a Cushing response indicating raised intracranial pressure. If this occurs, allow for the egress of fluid. 8. Proceed with the removal of the cyst: a. If the cyst is small, i. Coagulate the overlying choroid plexus, avoiding the fornix. ii. Coagulate the contralateral choroid plexus if possible. iii. Using a grasper, remove the cyst as a whole. If this cannot be achieved, coagulate and open the cyst, aspirating the contents. iv. Prepare a pediatric endotracheal suction catheter cut at 45 degrees. If the cyst is mucinous, the cut end can be used to morselize the cyst and aspirate its contents. v. Remove using forceps if the content is too dense to aspirate. b. If the cyst is large, i. Attempt to decompress the cyst through the foramen or the ipsilateral thinned-out septum pellucidum that is stretched over the underlying cyst. Beware that the ipsilateral fornix is also stretched over the cyst, and every attempt should be made to minimize damage to this structure. ii. Coagulate the cyst. iii. Proceed to aspirate the contents. 9. Once the content is removed, then dissect the cyst wall from the attachment to the roof of the third ventricle: a. Use coagulation, blunt dissection, or sharp dissection as necessary.
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TABLE 45.2 Important Factors in the Surgical Management of Colloid Cysts
A. Patient and Tumor Factors Does the cyst cause radiologic hydrocephalus? Does the patient have symptoms consistent with intermittent ventricular obstruction? Have other causes of the symptoms been ruled out? Is the patient fully informed and in favor of surgical removal of the cyst? Is the patient informed of the risks and benefits of the procedure? (Risks include temporary memory loss, recurrence, and death.) Is the cyst small (<1.5 cm)? Does imaging suggest the cyst is mucinous rather than dense? Is the cyst adherent to the fornix or internal cerebral veins?
B. Surgeon Factors Is the surgeon experienced and confident with the use of the endoscope, stereotaxy, and other instrumentation involved? Have key structures been identified and avoided in the surgical trajectory? Is the surgeon in communication with the team? • Is the staff familiar with the equipment and setup? • Is the anesthetist monitoring the patient’s vital signs for the Cushing reflex that may be caused by increased intracranial pressure as a result of failure of egress of fluid? • Is the assistant continually irrigating the ventricles, especially when coagulating the choroid plexus? Is the port patent to allow egress of fluid? • Are the assistants mindful to avoid accidentally bumping the surgeon or endoscope? Has the surgeon checked that the equipment is working prior to starting the procedure? Are the marked incision and patient positions correct? Is the opening the right size? Is it too small to allow for comfortable movement of the instruments or larger than necessary? Are the surgeon and staff able to work ergonomically? Are the equipment, screens, and patient bed positioned to allow for this? Is the view of the endoscope maintained? • If there is bleeding, is the surgeon able to achieve hemostasis? • If hemostasis cannot be achieved through irrigation, consider using an instrument as a means of tamponade, coagulation of the vessel, or as a last resort draining the ventricles before finding the source of bleeding. Is the surgeon prepared to convert the procedure to an open one if necessary?
b. Consider that complete removal may not be possible if part of the wall remains adherent to the internal cerebral veins or the fornices, in which case either coagulate the remnants or consider conversion to an open approach if you believe it could be removed using standard microsurgical techniques. 10. If hemorrhage occurs during the procedure, there are several techniques to achieve hemostasis: a. It is preferable to first control bleeding by irrigation; in most cases this is sufficient to achieve hemostasis. b. If the source of bleeding can be seen, use the endoscope to tamponade the vessel. This method may be especially important to preserve large venous structures. c. The vessel can also be coagulated via monopolar or bipolar probes, but this is difficult. d. As a last resort, it is possible to drain CSF from the ventricles and coagulate in an air-filled environment or to convert to an open approach if bleeding cannot be controlled. Draining CSF from the ventricles by injecting air into them to minimize the risk that they will collapse is strongly recommended. 11. At the end of the procedure, endoscopic exploration of both the lateral and third ventricles is important to remove any blood clots that may have formed. Fill the ventricles
with fluid before plugging the cortical opening with Gelfoam. A burr hole cover in bald patients is optional. Close in a layered fashion. A checklist of important factors in the planning of surgery is outlined in Table 45.2.
Neurocysticercotic Cysts Neurocysticercosis (NCC) is a condition caused by the larvae of the tapeworm Taenia solium. It is the most common form of parasitic infection of the brain, and most often manifests as seizures.55,56 Cysts in the ventricular system can cause obstruction to CSF and hydrocephalus.57 In such cases, patients have traditionally been treated with ventriculoperitoneal shunting.58 However, the endoscopic excision of cysts has been shown to be safe and effective, and it is now an increasingly preferred method of treatment.59–64 CSF diversion can also be achieved during surgery by the creation of a third ventriculostomy, further reducing the need for shunt placement.65 As with other endoscopic procedures, the careful assessment of preoperating imaging prior to operating is recommended. Determine the CSF spaces to be explored and the safest trajectory to examine each one. The method can be performed via a single approach with a flexible endoscope or as many as
CHAPTER 45 Endoscopic Approaches to Ventricular Tumors and Colloid Cysts
required with a rigid endoscope. Ensure that a disposable plastic sheath is used to maintain the transcortical path, as sometimes the entire metal sheath needs to be removed with the grabbing forceps in order to maintain the integrity of the cyst wall. If the cyst wall is ruptured and contents spill into the ventricle, then postoperative steroids will alleviate some of the symptoms of sterile meningitis. When using the rigid endoscope, if the ventricle is not drained, firm irrigation can mobilize ipsilateral cysts into view that can be secured with a pair of forceps and removed.
Miscellaneous Cysts When operating on other cysts, such as arachnoid cysts, it is important to keep the same principles in mind. Planning and visualization are key. Working within the fluid-filled space of the ventricles makes the endoscope ideal for fenestration of these cysts. However, the anatomy can often be distorted and the arachnoid surface thick and opaque. Therefore it is beneficial to use stereotaxis to assist in visualizing any anatomic structures may be hidden behind an opaque membrane prior to fenestration. Avoid blunt perforation, as this can inadvertently cause damage to neurovascular structures behind the target.
Intraventricular Tumor Resection As with colloid cysts, intraventricular tumors most amenable to endoscopic removal are those with the following characteristics: • Small • Relatively avascular • Partially or completely cystic and • Located in enlarged ventricles
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Ventricles of at least normal size should be present for tumors to be safely biopsied or resected.66,67 The following tumors are usually avascular and are appropriately treated using pure endoscopic techniques: • Subependymomas • Ependymomas • Subependymal giant cell astrocytomas associated with tuberous sclerosis • Neurocytomas • Exophytic low-grade gliomas • Hypothalamic hamartomas Choroid plexus and pedunculated tumors may also be suitable if the blood supply can be easily accessed and coagulated.
Planning In planning endoscopic intraventricular tumor resection, it is particularly important to choose a trajectory that minimizes excessive “windshield wiping.” This can cause damage to surrounding structures, such as the fornix lying at the anterior border of the foramen of Monro. The right trajectory (Fig. 45.3) is one with the following characteristics: 1. Has some normal ventricle between the entry point and the targeted pathology, which allows for better visualization of normal structures and orientation 2. Allows access to the blood supply 3. Allows access to the point of attachment to the ventricular wall or choroid plexus; if the blood supply and points of attachments can be disconnected early, the tumor can often be removed en bloc quickly rather than piecemeal 4. Does not originate in or traverse eloquent structures 5. Allows management of associated hydrocephalus or trapped CSF spaces B
A
Approach trajectory A
Approach trajectory B • Figure 45.3 Choosing an appropriate approach that allows normal ventricle to be traversed prior to encountering the tumor gives a better view of the anatomy of the tumor and surrounding structures. It also allows identification and disconnection of the blood supply. (Adapted with permission from Barrow Neurological Institute; originally published in Winn HR, ed. Youmans Neurological Surgery. 6th ed. Philadelphia: WB Saunders; 2011.)
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Neuronavigation can be useful in planning the right trajectory. For tumors in the third ventricle, draw a line from the anterior-most border of the tumor to the foramen of Monro; this can be extrapolated to find an appropriate entry point and angle. This line helps minimize proximal movement of the scope. Another important factor that should be considered and controlled is the risk of becoming disoriented. This is a major cause of complications in endoscopic resections of intraventricular tumors. It is minimized through the following: • Choosing the right trajectory • Careful examination and orientation of the equipment and video image prior to entering the brain • Knowledge of normal ventricular anatomy • Being aware of the optical distortion caused by the endoscope • Use of frameless stereotactic guidance
Method 1. Tap the ventricle using a brain needle or ventriculostomy catheter. 2. Use frameless stereotactic navigation to place a peel-away sheath down the tract. 3. Use cup forceps to obtain a biopsy of the tumor prior to coagulation to maintain specimen quality. 4. Coagulate feeding vessels and the surface of the tumor. Disconnect the tumor from its pedicle. 5. Ensure the assistant is continuously irrigating with lactated Ringer solution to prevent overheating within the ventricles and to control any bleeding. 6. It is preferable to remove the tumor as a whole: a. If this is not possible, consider breaking up its contents and aspirating with a pediatric endotracheal suction catheter cut at 45 degrees or a stainless steel cannula. b. Avoid piecemeal resection and migration of tumor through the ventricles. c. Endoscopic ultrasonic aspirators are available and may help with large tumors. 7. Once the bulk of the tumor has been removed, inspect the ventricles for any remaining remnants or blood clots, especially in the foramen of Monro or aqueduct of Sylvius. 8. When there is a risk of obstruction, some surgeons may elect to place an external ventricular drain, though the authors would not recommend its routine use due to the risk of infection. 9. A septum pellucidotomy or third ventriculostomy may be appropriate to prevent postoperative hydrocephalus.
The most common complication of tumor biopsy is intraventricular hemorrhage. Other complications include tension pneumocephalus, obstructive hydrocephalus, and large vessel injury. Tension pneumocephalus can be avoided by refilling the ventricles with lactated Ringer solution. To prevent intraventricular hemorrhage, ensure adequate visualization before attempting to manipulate any structures. Several techniques to manage hemorrhage were outlined previously.
Endoscope-Assisted Microsurgery Where an open microsurgical approach is more appropriate for the removal of intraventricular or periventricular tumors, endoscopy can still play an important role by extending the field of visualization. Examples of cases where endoscopy can be used to assist microsurgical procedures include the following: • The removal of intraventricular portions of craniopharyngiomas • Cyst fenestration and collapse prior to craniotomy to remove the solid component of a tumor Cystic and large tumors are particularly suited to this method, as the initial decompression of the lesion under microscopy creates a working space in which to manipulate the endoscope.69 This reduces the need for brain retraction and minimizes parenchymal damage. Diagnostic ventriculoscopy uses the endoscope for inspection purposes. A 30-degree scope is best suited in these cases, as it provides a wide field of view and minimizes the need for brain retraction. Ventriculoscopy can be used to perform various functions: • Identify ependymal tumor deposits not seen on MRI • Determine the patency of the aqueduct or other CSF pathways • Check for residual blood clots or tumor remnants
Process 1. Have the endoscopic equipment ready in the room for all patients. 2. Nursing staff should set up the endoscopic equipment while the surgeon achieves hemostasis under microscopy: achieving hemostasis prior to using the endoscope is especially important as its view can be easily obscured by bleeding. 3. Switch from microscope to endoscope: a. Introduce the endoscope under microscopic guidance. b. Elevate the microscope away from the patient so the endoscope may be reintroduced easily.
Biopsy of Intraventricular Tumors
Conclusion and Future Directions
Periventricular CNS lymphomas and “nonoperative” gliomas may be appropriately biopsied by the use of endoscopy. The difficulty of locating the tumor may be alleviated with the use of image guidance. The 5-ALA has also been reported to be a useful tool in identifying gliomas through an intact ependyma.68
The endoscope has truly revolutionized the way neurosurgeons approach brain tumors in general and intraventricular tumors in particular. The natural corridor that the ventricles provide makes endoscopy particularly applicable. Purely intraventricular tumors, such as colloid cysts and other avascular lesions, may be totally removed through a burr hole and a single
CHAPTER 45 Endoscopic Approaches to Ventricular Tumors and Colloid Cysts
atraumatic cortical corridor with excellent visualization, hemostasis, and angled inspection of the tumor bed to ensure the completeness of the resection. Endoscope-assisted microsurgery has been equally beneficial by enabling the surgeon to look around corners, remove tumors from multiple compartments without multiple entry points, and identify neurovascular structures early to prevent irreversible damage. Endoscopy in neurosurgery is a dynamic practice; advances are constantly occurring. Just as angled endoscopes provided superior access to previously obstructed views, curved and adjustable instruments are now allowing treatment of previously unseen pathologies. Combination instruments, such as the adjustable suction-bipolar, have allowed solo neurosurgeons to handle both the endoscope and the instruments simultaneously. In the future, advances facilitating endoscopic sharp dissection and hemostasis are welcomed. Also needed are sharper imaging modalities for both flexible and rod-lens endoscopes and better integration with stereotactic guidance systems. Major advances in both endoscope and instrument development will be aided by earlier integration of endoscopic techniques into training programs. As more and more neu-
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rosurgeons incorporate these techniques and approaches into their practices, the need for more precise viewing and accurate instrumentation will grow. Just as endoscopy has become a mainstay in other specialties, such as general surgery and orthopedic surgery, it will soon be a necessary skill for all neurosurgeons in order to offer their patients the best possible management options for intraventricular lesions. It is our hope that commercial vendors, engineers, and neurosurgeons can collaborate to continue advancing this field and to keep up with the steady and growing demand from current and future practitioners.
Selected Key References Abdou MS, Cohen AR. Endoscopic treatment of colloid cysts of the third ventricle. Technical note and review of the literature. J Neurosurg. 1998;89(6):1062-1068. Sheikh AB, Mendelson ZS, Liu JK. Endoscopic versus microsurgical resection of colloid cysts: a systematic review and meta-analysis of 1,278 patients. World Neurosurg. 2014;82(6):1187-1197. Please go to ExpertConsult.com to view the complete list of references.
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