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