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, which are easily aspirated, to a hard, 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 because of their poor durability. Microsurgical removal is effective but more invasive than the endoscopic approach.^20,23,31 Therefore, endoscopic removal is recommended in the majority of cases.^32–35 However, when imaging predicts the consistency of the cyst contents to be hard and cheesy, then 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 (careful not to injure the caudate head), is sufficient for removal.^24,36 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. 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.^21,37,38 Symptomatic relief of obstructive hydrocephalus is generally obtained, though mild ventriculomegaly often persists.³⁷

Neurocysticercotic Cysts

Neurocysticercosis (NCC) is the neurological manifestation of the parasite Taenia solium and 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.^39–41 Recently, pediatric data regarding neuroendoscopic cyst evacuation has been reported. The shunting rate is lower (22%) in the neuroendoscopic group than in 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).³⁹ Two other studies show complete resolution of cysts and no need for shunting with minimal transient morbidity.^40,41

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 because 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 are 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. 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 cysts 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 the important neurovascular structures that lie behind. Enlarging interhemispheric cysts can be fenestrated directly to the ventricle or via cystocisternoventricular fenestration.⁴² Fourth ventricular cysts obstructing outflow are also amenable to fenestration.⁴³

Pure Endoscopic Approaches

Endoscopic applications for intraventricular tumors include tumor biopsy, tumor resection, and management of tumor-associated hydrocephalus.^44,45 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.⁴⁶ 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.⁴⁷

One key to tumor resection within the ventricles is to select a proper working trajectory. Because 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.

A proper working trajectory is one that accomplishes the following:

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. 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 earlier, the use of transendoscope ultrasonic aspirators may speed up tumor removal if en bloc removal is not possible.²⁷

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.^48–50 Third ventricle tumor resections are particularly dependent on proper approach angle since 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 anteriormost 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 that 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.

Certain tumors are more amenable than others for endoscopic removal.⁵¹ 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, ependymomas, the subependymal giant cell astrocytomas associated with tuberous sclerosis, selected neurocytomas, exophytic gliomas (primarily pilocytic or low grade), and hypothalamic hamartomas.⁵² 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 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 case. Increased intracranial pressures 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 spinal fluid. Removing larger portions 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.⁵³ Normal saline is not used because it lacks electrolytes, is acidotic, alters the electrolyte balance in the brain, and leads to postoperative confusion.⁵⁴ Again, appropriate egress of irrigant will avoid a dangerous rise in intracranial pressure.

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 tumor.⁴⁷ 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.⁵⁵ The gelatinous contents of colloid cysts and some other cystic tumors respond particularly well to this technique. As mentioned earlier, 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.²⁷ 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. 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-aminolevulinic acid (5-ALA) fluorescence to identify and biopsy a midbrain glioma through an intact ependymal layer has been reported.⁵⁶

Complications of tumor biopsy and removal include intraventricular hemorrhage, neurological deficit, tension pneumocephalus, hydrocephalus, and basilar artery injury.^57–59 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 facemask will help with dissolution.⁶⁰

Peratta and associates reported an 8.8% complication rate for neuroendoscopic (nonhydrocephalus) procedures in pediatric patients.⁶¹ Hemorrhagic complications of tumor biopsy are reported at 3.5% per patient and 2.4% per procedure.⁶² 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. There are several techniques 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 to coagulate 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

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 the traditional microsurgical procedure that uses an endoscope as an adjunct either through the same opening or through a separate bur hole for better overall visualization. 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. Charalampaki and colleagues reported that endoscope-assisted microsurgery has been useful in 35 patients with traditional microsurgical approaches to the ventricular system done through keyhole craniotomies. Thirty-one out of 35 patients had no morbidity at 6 months and 3 of the patients with 6-month morbidity had preexisting Perinaud’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.⁶³ Another example of endoscope-assisted microsurgery is the transventricular management of craniopharyngioma including 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.⁶⁴

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 perforated, 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, hydrocephalus associated with tumors can be managed with the endoscope and is, in fact, preferable.