Six major advancements in the use of neuroendoscopy have occurred. A century ago, Lespinasse, a urologist, attempted a choroid plexus coagulation to treat hydrocephalus.^1,² In the early twentieth century Dandy and Mixter attempted endoscopic third ventriculostomy (ETV).³ In the 1970s technological advances allowed the production of flexible fiberscopes as well as rigid endoscopes. Throughout the late 1980s and 1990s ETV and decompartmentalization of the ventricular system were popularized, which allowed many neurosurgeons to become familiar with the tools of neuroendoscopy. This familiarity resulted in the fifth and sixth advances. The use of the endoscope for extra-axial lesions was popularized by pioneers such as Perneczky who championed the keyhole approach to aneurysms. The final and most recent wave of endoscopic enthusiasm has been its application to anterior skull base surgery, especially transsphenoidal and transtubercular surgery. The use of the endoscope for intraventricular neuro-oncological applications including lesion removal, tumor biopsy, and cyst management is also becoming more common, so much so that endoscopic colloid cyst surgery has results that are similar to those of microsurgery, and with a better risk profile.⁴^–⁸

Equipment

Equipment available for neuroendoscopy is constantly evolving. Basically, there are two types of endoscopes. The rigid endoscope is a fixed-length and fixed-geometry instrument that usually has several viewing angles available (0, 30, and 70 degrees to the long axis of the endoscope). The light source, camera, and shaft of the scope are all in-line and allow for easier orientation when working in the ventricular system.

The flexible fiberscope is maneuverable in three directions with relatively simple controls. The advantage of the flexible scope is that its geometry is not fixed and it may be fashioned to proceed along a curved trajectory such as traversing the foramen of Monro into the posterior third ventricle to biopsy a pineal tumor. This allows a single trajectory to treat hydrocephalus via ETV and sample the tumor (Fig. 41.1A and B). The flexible scope may also be used down the working port of the rigid scope in a “scope-in-scope” technique.⁹ The main drawbacks of the flexible scope over the rigid scope are the poorer optical resolution and that the surgeon may inadvertently withdraw the scope in the “bent” configuration with devastating repercussions.

FIGURE 41.1 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 bur hole approach used for endoscopic third ventriculostomy.

(Adapted with permission from Barrow Neurological Institute; originally published in Winn HR, editor. Youmans Neurological Surgery, 6th ed. Philadelphia: WB Saunders, 2011.)

Rigid endoscope-holding arms are available from several manufacturers and allow the scope to be secured rigidly in place. This addresses surgeon fatigue and dependence upon an assistant to hold the endoscope. These rigid arms are generally adjustable in all three planes. However, once set, they all have some degree of “play” or “float” for which the surgeon will need to account when positioning.

Frameless neuronavigation is helpful to guide insertion of the sheath, especially in the absence of ventriculomegaly, and for localizing lesions for biopsy under an intact ependyma.¹⁰ In the instance that the surgeon becomes disoriented or confused by distorted anatomy, stereotaxis can assist in reorientation.

Recently, several potentially important advances in instrumentation available to the endoscopic surgeon have been reported. The length of time required to aspirate a tumor using a “biopsy after biopsy” approach may be shortened by the use of traditional ultrasonic aspiration with a specialized handpiece down the working port of the endoscope. It has been used successfully on pituitary tumors, intraventricular clot removal, and craniopharyngioma cyst wall removal.¹¹ Endoneurosonography has been used to supply additional information about the relationship of the tip of the probe and structures orthogonal to it.¹² Water-jet dissection has been reported to be a useful adjunct in the safe perforation of a craniopharyngioma cyst wall, septum pellucidum, or floor of the third ventricle.¹³ This may help to decrease the risk of hemorrhage associated with blindly inserting an instrument through a thin structure such as the third ventricle floor.

Endoscopic Principles

Visualization is the key to neurosurgery. If you can’t see it you can’t safely operate on it. The endoscope offers all the visualization advantages of the microscope and allows them through a minimally invasive approach. This avoids unnecessary morbidity from brain retraction and large openings. Additionally, the magnification and illumination offered are superior to those offered by the microscope. Despite the visualization advantages afforded by the endoscope, the microscope still provides excellent visualization in a straight line and allows more precise, bimanual, three-dimensional microsurgical dissection. Rather than competing methods each method of visualization should be thought of as complementary to the other and both should be mastered to give the patient the best possible surgical treatment.

There are two principal forms of endoscopy: coaxial and extra-axial. Coaxial endoscopic approaches, or “pure” endoscopy, are those in which all components of the endoscopic system (lighting, camera, working channels, irrigant channels, and instruments) are all parallel and enclosed in a single sheath. The instruments are introduced through working channels and are aimed by redirecting the endoscope. The impact to the surrounding brain from removing and reintroducing instruments is minimized because the entire working and visualization area is within the endoscopic sheath. Most intraventricular endoscopic procedures are performed in a coaxial manner.¹⁴

Extra-axial endoscopic approaches are those in which the endoscope is the mode of visualization and the instruments are introduced alongside the endoscope separately. This generally applies to anterior skull base operations.

During “endoscope-assisted” applications, the microscope is the primary mode of visualization, and the endoscope is used to improve visualization, especially around corners and behind “unmovable” structures.

During “endoscope-controlled” surgery, the endoscope is the sole mode of visualization and surgery is performed using the same techniques and instrumentation as microsurgery, with the addition of curved instruments and suctions that allow the surgeon to operate around corners. In these forms of endoscopy, a substantial learning curve exists because of peripheral distortion, angled view when using non-0 degree endoscopes, and the close proximity of the surgical field to the tip of the endoscope. Once this is overcome, these same “problems” may be used to the surgeon’s advantage, resulting in better outcomes.

Intraventricular Endoscopy for Cysts

Colloid Cysts

Colloid cysts of the third ventricle are non-neoplastic masses that typically arise from the roof of the third ventricle. They can occlude the foramen of Monro, causing headache, hydrocephalus, memory disturbances, and sudden death. Colloid cysts have a variable consistency, from mucinous, that are easily aspirated, to a hard and cheesy consistency. Cysts 1 cm or larger and those causing symptoms or hydrocephalus are generally recommended for removal. Other options including shunting and stereotactic drainage are possible but not recommended owing to their poor durability. Microsurgical removal is effective but more invasive than the endoscopic approach.^4,^5,¹⁵ Therefore, endoscopic removal is recommended in the majority of cases.¹⁶^–¹⁹ However, when imaging predicts the consistency of the cyst contents to be hard and cheesy the cyst is better removed microsurgically with bimanual dissection. Additionally, cysts larger than 2 cm may compromise or adhere to the fornix and may be more safely removed using microsurgical bimanual dissection.

A single bur hole, approximately 8 cm behind the nasion and 5 to 7 cm lateral to the midline in the nondominant hemisphere (be careful not to injure the caudate head), is sufficient for removal ^7,²⁰ (Fig. 41.2). Image guidance helps with the initial ventricular entry. A peel-away sheath is optional. The landmarks of the colloid cyst and foramen of Monro are identified and the overlying choroid plexus is coagulated, avoiding the fornix. The cyst is coagulated and opened and the contents are aspirated. A pediatric endotracheal suction catheter with the end cut to 45 degrees is particularly effective if the consistency is favorable. Alternatively, some endoscope manufacturers have designed rigid endoscopic suction that uses either blunt or beveled tips and works well to suction the mucinous material. One can twist the catheter and use the cut end as a dissector to “morselize” the contents of the cyst prior to aspiration. If the contents are too dense, forceps may be required to empty the cyst contents. The wall of the cyst is then dissected free of the roof of the third ventricle with generous coagulation. Generally the cyst wall is not densely attached to the fornix and can be removed completely. However, in the case that the wall is so adherent to the internal cerebral veins or the fornix that it cannot be separated using either sharp or blunt dissection it may be prudent to leave a thin “carpet.” Under these circumstances, the recurrence rate appears to be low, but we must await reports of long-term outcome.^6,^21,²² Symptomatic relief of obstructive hydrocephalus is generally obtained, though mild ventriculomegaly often persists.²¹

FIGURE 41.2 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.

Neurocysticercotic Cysts

Neurocysticercosis (NCC) is the neurological manifestation of the parasite Taenia solium. This is commonly contracted in underdeveloped countries by hand-to-mouth contamination from unclean water or food. NCC most often presents with seizures but may also present with sudden hydrocephalus due to intraventricular cysts blocking normal cerebrospinal fluid (CSF) pathways. There is a growing body of literature suggesting that neuroendoscopic removal of cysts results in improved patient outcomes and lessens or avoids altogether the need for shunting.²³^–²⁵ Recently, pediatric data regarding neuroendoscopic cyst evacuation has been reported. The shunting rate is lower (22%) in the neuroendoscopic group than the traditional medical treatment group (70%) and the Karnofsky performance scale was higher in the endoscopic group (90.0% vs. 85.5%, p = 0.003).²³ Two other studies show complete resolution of cysts and no need for shunting with minimal transient morbidity.^24,²⁵

The procedure is performed either through a single approach with a flexible endoscope or through as many approaches as needed with the rigid endoscope. A disposable plastic sheath is mandatory in order 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 spilled into the ventricle, then postoperative steroids will alleviate some of the symptoms of sterile meningitis. Preoperative imaging will determine what CSF spaces need to be explored and the safest way to explore each. The advantages and disadvantages of each type of endoscope have been previously discussed. 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 forceps and removed.

Miscellaneous Cysts

Other cysts, such as arachnoid cysts, occur within the ventricles. Often fenestration of these to normal CSF spaces is desirable. The ease of working in a fluid-filled space makes the endoscope ideal for fenestration. The anatomy is often distorted and the arachnoid surface is often thick and somewhat opaque. Stereotaxis is very helpful in these cases to know what is behind an opaque membrane prior to fenestration. Blunt perforation should be avoided at all costs as pushing against these flimsy membranes may damage important neurovascular structures that lie behind. Enlarging interhemispheric cysts can be fenestrated directly to the ventricle or via cystocisternoventricular fenestration.²⁶ Fourth ventricular cysts obstructing outflow are also amenable to fenestration.²²

Intraventricular Endoscopy for Tumors

Endoscopic applications for intraventricular tumors include tumor biopsy, tumor resection, and management of tumor-associated hydrocephalus.^27,²⁸ In general, neuroendoscopy for tumors is a step up in technical difficulty from the endoscopic management of hydrocephalus. The ideal conditions for endoscopic resection of an intraventricular tumor are that it should be small, avascular or with relatively low vascularity, partially or totally cystic, and located in enlarged ventricles. Hydrocephalus creates an ideal working space. However, a normal ventricle is adequate to gain access to a tumor and biopsy it and, for smaller tumors, to resect it safely.^29,³⁰ A recent report even suggests that in experienced hands, operating in a normal-sized ventricle yields the same success/complication rate as operating in large ventricles.

One key to tumor resection within the ventricles is to select a proper working trajectory. Because the brain must be transited in order to reach the ventricles, a single working angle that does not require excessive “windshield wiping” of the endoscope should be chosen.

Considerations when selecting an approach trajectory are to select one which:

1. Enters the ventricle with some normal ventricle between the entry point and the mass

2. Allows access to the blood supply, if vascular

3. Allows access to the point of attachment to the ventricular wall or choroid plexus

4. Does not originate in or traverse eloquent structures

5. Allows management of associated hydrocephalus or trapped CSF spaces

Having some normal ventricle and CSF between the entry point into the ventricle and the tumor allows better visualization of the tumor margin and allows visualized normal structures to aid in orientation (Fig. 41.3). Access to the blood supply and point of attachment may turn a tedious piecemeal tumor resection into a disconnection and en bloc removal. As mentioned above, the use of transendoscope ultrasonic aspirators may speed up tumor removal if en bloc removal is not possible.¹¹

FIGURE 41.3 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, editor. Youmans Neurological Surgery, 6th ed. Philadelphia: WB Saunders; 2011.)

Image guidance is particularly valuable for approach planning and execution, and is worthwhile even if it is only used for this step of the procedure.³¹^–³³ Third ventricular tumor resections are particularly dependant on proper approach angle because often the endoscope must traverse the foramen of Monro, putting the fornix, at the anterior border of the foramen, at some risk. Image guidance allows the surgeon to use trajectory views to draw a line from the anterior border of the tumor to the anterior-most border of the foramen of Monro. This line can then be extended to the surface to choose the appropriate entry point and angle. The fornix will not tolerate anterior “windshield wiping” movements of the endoscope while its tip lies in the third ventricle. Posterior movements are tolerated much better; however, the venous structures coalescing at the posterior margin of the foramen of Monro also limit scope excursion. Fortunately, many intraventricular tumors are associated with ventriculomegaly and an enlarged foramen of Monro that allows for larger excursions of the endoscope.

It is worth noting the major source of complications in intraventricular endoscopic approaches for brain tumors is disorientation. Complications can be minimized through appropriate entry point and trajectory choice, prior orientation of the camera, detailed examination of the equipment and video image prior to entry into the brain, a thorough knowledge of normal ventricular anatomy, and a constant self-inquiry into where the endoscope is, what all structures seen represent, and how the endoscope’s intrinsic optical distortion is affecting the scene. The use of frameless stereotaxis helps reduce disorientation.

Endoscopic Approaches to Intraventricular Tumors

Details of the diagnosis, pathology, and nonsurgical treatment of intraventricular tumors are discussed in Chapter 42. Certain tumors are more amenable than others for endoscopic removal.³⁴ When working within the fluid-filled ventricle, bleeding may be difficult to control and obscures the operative field. Therefore, tumors of low vascularity are preferred for purely endoscopic removal. Examples are subependymomas, some ependymomas, the subependymal giant cell astrocytomas associated with tuberous sclerosis, selected neurocytomas, exophytic gliomas (primarily pilocytic or low grade), and hypothalamic hamartomas.³⁵ Some vascular tumors such as choroid plexus and pedunculated tumors can also be approached endoscopically, because the blood supply is often well defined and easy to coagulate and divide.

The technique of endoscopic tumor removal requires a high level of familiarity with the endoscope and its use, as it represents one of the most technically complex skills in neuroendoscopy. A peel-away sheath is recommended. Its purpose is to avoid buildup of irrigant and increased intracranial pressure, and thus to allow the endoscope to be removed and replaced with ease, especially when the forceps and endoscope are removed together with pieces of tumor that are too large to come up the working channel. The advantage of not using the peel-away sheath is to slightly reduce the size of the track through the brain and to keep some pressure in the ventricle to reduce venous bleeding. The surgeon must communicate effectively with the anesthesiologist during the proceduree. Increased intracranial pressures (ICPs) will generally be manifest by a Cushing’s response and will be noted by the anesthesiologist. In this case, one should allow egress of fluid so that the hemodynamic values return to normal.

Piecemeal tumor removal can be very tedious and also lead to tumor spread if fragments are released that float free in the CSF. Removing larger chunks of tumor and drawing them out with the endoscope is more efficient and leads to higher quality specimens.

Prior to placing the peel-away sheath, tapping of the ventricle with a brain needle or a ventriculostomy catheter is recommended. The peel-away sheath can then be placed down the tract using image guidance. The bluntness sometimes also results in the tip deflecting from the ependyma. This problem is overcome when a smaller bore, sharper instrument violates the ependyma.

Most tumors are approached by taking initial biopsy specimens with cup forceps, minimizing coagulation to maintain the quality of the tissue for analysis. Any vessels on the surface of the tumor are then coagulated. Electrocautery (especially monopolar) is capable of generating high CSF temperatures and must be used with caution. Irrigation with warmed lactated Ringer’s solution or a spinal fluid substitute solution is used to dissipate this heat.³⁶ Normal saline is not used because it lacks electrolytes, is acidotic, alters the electrolyte balance in the brain, and leads to postoperative confusion.³⁷Again, appropriate egress of irrigant will avoid a dangerous rise in ICP.

Once bleeding is controlled, cautery, blunt dissection, and bites with the forceps or scissors are used to separate the tumor from the normal tissue. The best tumors for neuroendoscopy have a distinct margin and can be gently retracted away from the surrounding tissue. Ideally, a perimeter can be created, the tumor can be isolated as a mass, and it can be removed in one or more large pieces. If the tumor is soft, multiple methods of tumor aspiration are possible. A stainless steel suction cannula or the previously mentioned pediatric endotracheal suction catheter placed down the working channel can be used to morselize and aspirate the tumor.³⁸ Shortened endovascular catheters can also be used. They have the advantage of a stiffer, thinner wall that can be shaped. The catheter allows a larger inner lumen diameter for more efficient aspiration of appropriate consistency tumors.³⁹ The gelatinous contents of colloid cysts and some other cystic tumors respond particularly well to this technique. As mentioned previously, the length of time required to aspirate a tumor using a “biopsy after biopsy” approach may be shortened by the use of ultrasonic aspiration with a specialized handpiece down the working port of the endoscope.¹¹ Regardless of the removal technique, every attempt should be made to avoid dispersion of tumor remnants throughout the ventricles.

After satisfactory tumor removal, attention is paid to hemostasis, usually by irrigation alone. The ventricle is inspected for residual tumor and blood clots, particularly over the foramen of Monro or the aqueduct of Sylvius, where obstruction may occur. The decision about whether or not to leave an external ventricular drain is controversial, and should depend primarily on the risk of obstruction. In cases in which the working trajectory allows it, addition of a septum pellucidotomy or third ventriculostomy may decrease the chance of postoperative symptomatic hydrocephalus.

In some cases tumor biopsy rather than removal may be the goal. Central nervous system (CNS) lymphoma is often periventricular and amenable to endoscopic biopsy for diagnosis. “Nonoperative” gliomas may also be appropriate for this biopsy method. Stereotactic guidance is helpful in locating the tumor. However, identification of the tumor tissue through overlying normal ependyma may be problematic. Recently, the use of 5-ALA (5-aminolevulinic acid) fluorescence to identify and biopsy a midbrain glioma through an intact ependymal layer has been reported.⁴⁰

Complications of tumor biopsy and removal include intraventricular hemorrhage, neurological deficit, tension pneumocephalus, hydrocephalus, and basilar artery injury.⁴¹^–⁴³ Tension pneumocephalus results from air being exchanged for CSF during the procedure. To avoid this, the ventricles should be refilled with lactated Ringer’s solution. If large quantities of air remain, 100% oxygen administered via face mask will help with dissolution.⁴⁴

Peretta and associates reported an 8.8% complication rate for neuroendoscopic (nonhydrocephalus procedures) in pediatric patients.⁴⁵ Hemorrhagic complications of tumor biopsy are reported at 3.5% per patient and 2.4% per procedure.⁴⁶ To minimize the incidence of hemorrhagic complications one should never cut or pull any structure without being able to visualize the structure completely.

Hemorrhage is often the rate-limiting step during endoscopic tumor removal. Several techniques can be used to control hemorrhage with the endoscope. The first maneuver is to patiently irrigate. Most bleeding in the ventricle will stop with irrigation alone. The second maneuver is to attempt coagulating the bleeding source, but only if it can be directly visualized. Visualization may be improved by draining the CSF and working in an air-filled ventricle. A third maneuver is to gently tamponade the bleeding point using the endoscope itself or an instrument placed down the working channel. This maneuver is appropriate for larger veins that one is attempting to preserve such as the thalamostriate vein. An external ventricular drain can be left if necessary or as a “safety valve” in the case that tumor or hemorrhage occludes the foramen or aqueduct. The question of whether to leave a drain is not convincingly answered in the literature. We do not routinely leave drains after endoscopic procedures.

Endoscope-Assisted Microsurgical Approaches to Intraventricular Tumors

Many intraventricular tumors cannot be completely removed through a purely endoscopic approach, but endoscopy still maintains an important role. The concept of “endoscope-assisted” refers to a procedure whereby the approach is the traditional microsurgical one and the endoscope is used as an adjunct either through the same opening or through a separate bur hole for better overall visualization.⁴⁷ The endoscope allows the surgeon to look around corners and to visualize structures that are not visible by microscopic imaging alone, thus expanding the operating field. Utilizing angled endoscopes can maximize the area of the ventricle visualized. Endoscope-assisted microsurgery has been shown to be useful in 35 patients with traditional microsurgical approaches to the ventricular system done through keyhole craniotomies; 31 of the 35 patients had no morbidity at 6 months and three of the patients with 6-month morbidity had preexisting Parinaud’s syndrome that persisted. Seventy-eight percent of patients had complete tumor resections. One procedure was aborted due to hemorrhage and was repeated successfully with gross total removal 2 days later.⁴⁸ Another example of endoscope-assisted microsurgery is the transventricular management of craniopharyngioma. This includes gross total removal of intraventricular components, fenestration of cysts as a stand-alone procedure for symptomatic control, and cyst fenestration followed by collapse and subsequent craniotomy for definitive removal of the solid component.⁴⁹

Additionally, diagnostic ventriculoscopy should be performed whenever an endoscope is placed in the ventricle for any reason. With a 30-degree endoscope a wide inspection can often be performed by rotation of the endoscope without any additional brain retraction. For example, ventriculoscopy can identify ependymal tumor deposits that cannot be seen on magnetic resonance imaging (MRI), can confirm whether the septum pellucidum is patent or perforate, and whether the opening of the aqueduct is obstructed or open. In patients undergoing shunting, ventriculoscopy can be performed before the catheter is placed, or through the endoscope with a fiberscope. In most cases, however, endoscopic management of hydrocephalus associated with tumors can be performed and is in fact preferable.