Endoscopic Brain Surgery: Ventriculostomy and Colloid Cysts

Endoscopic brain surgery reaches deep structures through a burr hole, a small hole drilled in the skull. Its main uses are endoscopic third ventriculostomy (ETV) for obstructive hydrocephalus, removal of colloid cysts, endoscopic transsphenoidal surgery for pituitary tumours and assistance in microvascular decompression. Around the endoscope sits a layered toolkit: navigation, fluorescent dye, functional and intraoperative MRI, Gliadel wafers and Gamma Knife.

Modern cranial neurosurgery is defined less by any single instrument than by that combination: the endoscope to reach deep structures, stereotactic and navigation systems to locate a target in three dimensions, fluorescent dye and intraoperative MRI to show where tumour ends and brain begins, functional MRI to identify the areas a patient cannot afford to lose, and radiosurgery and local chemotherapy for disease that surgery alone cannot control. Dr. Anil Kumar Kansal, Vice Chairman & HOD - Neuro Surgery & Neuro Spine, BLK-Max Super Speciality Hospital, New Delhi, India, uses all of these in his neurosurgery practice, often in combination on the same patient.

This article sets out how each tool is used, which problems it solves, and where Dr. Kansal is cautious about a technique's limits.

What endoscopic brain surgery treats

The neuroendoscope treats hydrocephalus, intracranial cysts and pituitary tumours, and assists in microvascular decompression. Endoscopic third ventriculostomy has been part of Dr. Kansal's practice for a long time. The endoscope's role has since widened to complex cases, including multiloculated hydrocephalus and intracranial cysts, and to endoscopic transsphenoidal surgery for pituitary tumours. It also assists in microvascular decompression.

How endoscopic third ventriculostomy (ETV) works

ETV is a bypass: the surgeon makes a small opening in the floor of the third ventricle so that fluid can drain around a blockage. In the hydrocephalus it treats, a build-up of cerebrospinal fluid in the brain's ventricles, the blockage usually lies at the cerebral aqueduct, below the third ventricle, so cerebrospinal fluid cannot drain onward. Through a small burr hole in the skull, the endoscope is guided through the foramen of Monro into the third ventricle. The surgeon identifies the landmarks, including the choroid plexus and the foramen, and then makes a small opening in the membrane forming the floor of the third ventricle. Fluid now has a route around the obstruction, and the hydrocephalus is relieved.

Colloid cyst: symptoms and endoscopic removal

A symptomatic colloid cyst, or one obstructing the flow of cerebrospinal fluid, should be removed; untreated, it can cause sudden collapse and death. Colloid cysts receive his most direct clinical advice of the session. They are small, benign cystic tumours located at the junction of the lateral ventricle and the third ventricle, where they obstruct the passage of cerebrospinal fluid from the lateral ventricles into the third.

Colloid cyst symptoms

Their danger lies in how they present. Patients usually have headache and sudden drop attacks, and the condition carries high mortality: a patient can develop raised intracranial pressure, collapse, and never regain consciousness, or die during that episode. The mechanism behind the sudden deterioration is a ball-valve effect, in which the cyst intermittently blocks both foramina. On imaging, the lateral ventricles are dilated while the third ventricle is not, because the fluid cannot pass from one to the other.

His message to referring doctors is unambiguous: a symptomatic colloid cyst, or one causing hydrocephalus, should be removed, by open surgery or endoscopically, whichever is available. A small cyst found incidentally, with no symptoms and no ventricular dilatation, can be monitored with serial imaging. His preference is the endoscope, because the incision is small and the risk is low.

How a colloid cyst is removed endoscopically

The endoscopic operation he demonstrated follows a clear sequence:

1. Make a small burr hole and pass the endoscope into the lateral ventricle. The septum is thinned out, and the third ventricular structures cannot be seen because the cyst is blocking the view.
2. Make an opening in the septum so that both lateral ventricles communicate and effectively become one.
3. Puncture the cyst and aspirate its colloid contents to decompress it.
4. Once the contents are out, use gentle suction to bring the collapsed cyst into the lateral ventricle and remove it, then remove the cyst wall.
5. Inspect the third ventricle, clear any remaining portion, and coagulate the choroid plexus on the opposite side.

At the end, the structures of the third ventricle and its floor are visible again. A post-operative scan in another case he showed had no residual colloid cyst. Dr. Kansal calls this a wonderful operation for a simple reason: a potentially fatal lesion is removed through a small incision with a good result.

Stereotaxy and neuronavigation: finding the target

Stereotaxy and neuronavigation locate a target in three dimensions before and during surgery.

Frame-based stereotaxy

Stereotactic surgery, which guides instruments to a point defined by three-dimensional coordinates, is how Dr. Kansal's team reaches deep-seated targets with precision. For a biopsy of a deep tumour, a stereotactic frame is applied to the head and the target is defined on CT in three coordinates, X, Y and Z. A small hole is made and the instrument advanced to that exact point. The same frame-based approach is used to place electrodes in the subthalamic nucleus for Parkinson's disease, covered in deep brain stimulation for Parkinson's: timing and cost.

Frameless navigation

Frameless systems use fiducial markers, reference points visible on the scan, in place of the frame. The markers register the patient's anatomy to the imaging, allowing the surgeon to localise a tumour and plan its removal under neuronavigation. Navigation shows the surgeon, throughout the operation, where the instrument is relative to the tumour, which Dr. Kansal credits with helping achieve complete excision.

Fluorescence-guided brain tumour surgery

Navigation shows where a tumour should be; fluorescence shows what is tumour. Dr. Kansal's team uses fluorescent dye for this. The agents in mainstream use are 5-aminolevulinic acid (5-ALA), taken by mouth a few hours before anaesthesia, and sodium fluorescein, given intravenously, which stains tumour tissue yellow-green. Under the microscope, tumour tissue takes on a different colour from the surrounding brain, so the surgeon can distinguish the two directly at the resection margin and remove the tumour completely.

The technique has one equipment requirement: a microscope fitted with a special filter, without which the fluorescence cannot be seen.

Functional MRI, intraoperative MRI and awake craniotomy

Three tools protect function when a tumour lies near critical brain: functional MRI before surgery, intraoperative MRI during it, and, selectively, awake craniotomy.

Functional MRI before surgery

When a tumour lies near critical brain, the first step happens pre-operatively. Functional MRI identifies which areas of the brain control specific functions; those areas are marked and avoided during surgery.

Intraoperative MRI

In a centre with an intraoperative MRI suite, the team can scan the patient during the operation after removing the tumour, check whether any tumour has been left behind, and remove it before closing. It closes the loop between what the surgeon believes has been removed and what the imaging shows.

Awake craniotomy limitations

Awake craniotomy depends on the patient staying cooperative throughout, and Dr. Kansal is cautious about it. A referring doctor from Uganda asked about its limitations in the Live Discussion. Awake craniotomy is used when the tumour sits in an eloquent area, such as the motor or speech cortex, where the patient remains awake and cooperative so that movement or speech can be protected during removal. Dr. Kansal is candid that he is not very fond of it.

His reasons are practical:

• Patient cooperation is essential throughout. In a recent case, the patient began shaking during surgery and the team had to convert to full general anaesthesia.
• Sedation is unpredictable. Under partial anaesthesia or sedation, some patients behave abnormally, even after agreeing to the approach in a pre-operative discussion.
• Language is a barrier for international patients. With Indian patients it is easier. During the procedure the patient communicates with the anaesthesia team and technicians rather than directly with the surgeon, so with international patients a translator sometimes has to be kept inside the operating theatre.
• It is tough on the patient.

He still uses it selectively, for patients with a tumour in the motor strip or another eloquent area who are comfortable with the approach after discussion. What his team now does is functional mapping with functional MRI before surgery, preserving the mapped areas during the operation. For international referrals in particular, that shifts much of the functional protection from the operating theatre to the planning stage.

Gliadel wafers for glioblastoma

Gliadel wafers deliver chemotherapy directly into the tumour bed after glioblastoma, an aggressive primary brain tumour, has been removed. Glioblastoma has a poor prognosis, and recurrence is the central problem. For newly diagnosed and recurrent glioblastoma, Dr. Kansal's team places Gliadel wafers, a carmustine chemotherapy implant, directly in the tumour bed after resection.

The rationale is local delivery. After the tumour is removed, up to eight wafers are placed in the cavity, the number depending on its size, and they are commonly covered with oxidised regenerated cellulose to hold them in place. They release chemotherapy directly into the tumour bed. In the randomised trial in newly diagnosed glioblastoma, carmustine wafers extended median survival by about two months compared with placebo.

Two observations frame its use. First, it is costly, so its use depends on what the patient can afford. Second, it adds little operative difficulty: once the resection is done, placing the wafers is easy. His team has used it in many patients. Indicative costs for craniotomy and brain tumour excision are listed separately.

Gamma Knife radiosurgery: indications

Gamma Knife radiosurgery delivers a high dose of radiation in a single session or, in some cases, multiple sessions, to control a lesion or reduce its size. Dr. Kansal's indications include:

• Small meningiomas
• Small vestibular schwannomas
• Residual tumour from previous surgery
• Arteriovenous malformations (AVMs), abnormal tangles of arteries and veins
• Metastases

Most of these are small lesions, or tumour left over after an earlier operation, which places radiosurgery alongside surgery rather than in competition with it.

How the toolkit combines

The value of these technologies lies in their combination. A single tumour operation in Dr. Kansal's practice may involve functional MRI to map eloquent cortex, navigation to localise the tumour, fluorescent dye under a filtered microscope to define its margin, and intraoperative MRI to confirm the resection, with Gliadel wafers or Gamma Knife reserved for what surgery cannot control. Each layer reduces a specific source of error: missing the target, leaving tumour behind, or damaging function.

What these advances mean for surgical risk, including the deficit and complication rates Dr. Kansal quotes for brain tumour surgery, is set out in recent advances in spine and neurosurgery: a complete guide.