Brain Tumour Surgery Techniques: Navigation to Gamma Knife

Modern brain tumour surgery techniques solve one problem: reaching a deep target without damaging the brain in the way. Stereotaxy and neuronavigation fix the target before the skull is opened, fluorescent dye and intraoperative MRI show what remains of a tumour while there is still time to remove it, and chemotherapy wafers and Gamma Knife radiosurgery carry treatment further. The endoscope does the same for lesions inside the ventricles.

The brain in the way is precious, and each of these advances solves one part of that problem. Dr. Anil Kumar Kansal, Vice Chairman & HOD - Neuro Surgery & Neuro Spine, BLK-Max Super Speciality Hospital, New Delhi, India, uses all of them in his neurosurgery practice, and he is precise about which question each one answers.

Locating the tumour before surgery: stereotaxy and neuronavigation

Stereotaxy, a method of locating a target in the brain by three-dimensional coordinates, and its frameless successor, neuronavigation, fix the position of a lesion before the skull is opened.

Frame-based stereotaxy

For a small, deep-seated lesion, a stereotactic frame is applied to the head and the target is defined by X, Y and Z coordinates. The surgeon then reaches the lesion through a small hole. The same coordinate method is used to place electrodes in Parkinson's disease.

Frameless stereotaxy and neuronavigation

In frameless stereotaxy, fiducial markers, small reference points visible on the scan, replace the frame. The target is planned on the images and a biopsy can be taken without a frame. Neuronavigation extends this to open surgery: the images are stored in the system and used to guide the operation. Dr. Kansal identifies three gains:

• the tumour can be marked and the approach planned before surgery;
• the craniotomy, the opening made in the skull, can be smaller;
• the tumour can be taken out completely.

Robotic assistance for electrode placement

The planned trajectory that underlies stereotaxy is also what a surgical robot executes. In the brain, Dr. Kansal's team already uses robotic help to place electrodes, in the same way that robots now guide screw placement in the spine. He describes the technology as evolving rapidly, with its role confined for now to placement along a planned path, and a long way still to go before it takes on more of the operation.

Fluorescence-guided brain tumour surgery and intraoperative MRI

Fluorescent dye and intraoperative MRI let the surgeon see remaining tumour during the operation, so that it can be removed completely.

Fluorescence-guided resection

A yellow dye is given before surgery. Viewed through a yellow filter on the operating microscope, tumour tissue changes colour, so it can be distinguished from normal brain and removed completely. The agent used with a yellow microscope filter is sodium fluorescein, given intravenously, which accumulates where the blood-brain barrier is disrupted and makes tumour tissue fluoresce yellow-green.

Dr. Kansal stresses that the technique matters most when the tumour lies in eloquent areas, such as those governing movement or speech. In those locations, telling tumour apart from functioning brain is what makes complete removal possible without causing a new deficit.

Intraoperative MRI

Intraoperative MRI helps to localise the tumour, to establish the diagnosis and to achieve complete resection. Quotations from Indian hospitals for open tumour removal are summarised under craniotomy and brain tumour excision cost.

Gliadel wafers for recurrent glioblastoma

Gliadel wafers are small chemotherapy implants placed in the cavity after a recurrent glioblastoma is removed, where they release the drug directly at the tumour site. Glioblastoma is a highly malignant brain tumour with a life expectancy of under two years. After surgery, patients receive radiotherapy and chemotherapy, and the tumour typically returns within six months to two years.

When a recurrent glioblastoma is re-operated, chemotherapy wafers can be placed in the cavity after the tumour is removed. Gliadel wafers are small button-like implants. Dr. Kansal typically places five, six or seven in the cavity. They release chemotherapy slowly and directly at the tumour site, which limits the systemic side effects of chemotherapy given by mouth or vein. He considers them a useful addition to the options for recurrent tumours, although they are costly.

The wafers contain carmustine, and up to eight can be placed in a resection cavity. They are approved for both newly diagnosed high-grade glioma and recurrent glioblastoma; in the pivotal trial in recurrent glioblastoma, median survival was about 31 weeks with the wafers against about 23 weeks with placebo wafers.

Gamma Knife radiosurgery: which brain tumours it treats

Gamma Knife radiosurgery delivers a single, highly focused dose of radiation that destroys the target tissue without an incision. Dr. Kansal uses it for:

• small meningiomas;
• small tumours of the cerebellopontine angle and the cavernous sinus;
• arteriovenous malformations (AVMs), tangles of abnormal blood vessels;
• deep-seated tumours;
• metastases, where they are few in number;
• recurrent tumours.

Its value, in his account, is that a number of operations can now be avoided altogether. The advantages are that it is non-surgical and non-invasive, gives good tumour control, and usually requires only one or two sessions. Newer Gamma Knife systems can immobilise the head with a thermoplastic mask instead of a rigid head frame, which also makes treatment in several sessions practical.

Endoscopic brain surgery for hydrocephalus and colloid cysts

Neuroendoscopy passes a thin camera into the fluid-filled ventricles of the brain through a single burr hole, a small opening drilled in the skull. Dr. Kansal uses it for a defined set of problems:

• Hydrocephalus, a build-up of fluid in the brain, by endoscopic third ventriculostomy.
• Multiloculated cysts, by fenestrating the cyst walls so the compartments drain together.
• Small tumours within the ventricles, which can be removed through the endoscope.
• Pituitary surgery, by the endoscopic transsphenoidal route through the nose.
• Microvascular decompression, assisted by the endoscope.

Endoscopic third ventriculostomy

Endoscopic third ventriculostomy (ETV) treats hydrocephalus by making an opening in the floor of the third ventricle. The procedure begins with a small burr hole. The endoscope is passed into the lateral ventricle, through to the third ventricle, and a hole is made in the floor of the third ventricle. Irrigation keeps the view clear throughout.

ETV vs shunt for congenital hydrocephalus in children

For a young child, Dr. Kansal regards endoscopic third ventriculostomy as the better choice than a shunt, and he set out the trade-off in numbers in the masterclass Live Discussion. Endoscopic third ventriculostomy succeeds in around 70 to 80% of selected children with obstructive hydrocephalus, such as aqueductal stenosis, in his figures. A programmable shunt controls the hydrocephalus in about 95%, but shunt failure and infection are further risks. Once a ventriculostomy has succeeded, the chance of the problem recurring is very low. Quotations for shunt surgery are summarised under VP shunt surgery for hydrocephalus cost.

Colloid cysts: a benign lesion with a dangerous position

A colloid cyst is benign, but it sits at the junction of the lateral and third ventricles, where it can block the flow of fluid from one to the other. Patients develop severe headache and fainting, and the condition can be fatal.

There are two ways to remove it. Microsurgical excision requires opening a large portion of the brain and carries higher morbidity and mortality. Endoscopic removal needs only a small burr hole. Dr. Kansal showed the endoscopic operation step by step:

1. Through the burr hole, the endoscope enters the lateral ventricle. The foramen of Monro and the choroid plexus come into view, but the third ventricle cannot be seen because the cyst blocks it.
2. The septum between the two lateral ventricles, very thin and flimsy, is opened so that both lateral ventricles communicate.
3. The cyst wall is opened with bipolar cautery and its contents are aspirated through a suction catheter, decompressing the cyst.
4. With gentle traction, the collapsed cyst is drawn out of the third ventricle into the lateral ventricle and removed, and the field is checked for any remnant.
5. The floor of the third ventricle becomes clearly visible, confirming that the foramen of Monro is open and the lateral and third ventricles communicate again.

The post-operative scans he showed have the ventricles decompressed and the cyst gone.

How brain tumour surgery techniques fit together

Each tool answers a different question, and none replaces surgical judgement. Stereotaxy and navigation answer where the lesion is. Fluorescence and intraoperative MRI answer whether it has all been removed. The endoscope answers how to reach a ventricular lesion without crossing healthy brain. Wafers and radiosurgery answer what to do when the knife alone is not enough. Used together, they let the surgeon remove more tumour through a smaller opening, with less damage on the way in.

Functional procedures that share some of this equipment, deep brain stimulation and microvascular decompression, are covered in trigeminal neuralgia treatment and deep brain stimulation. The wider principles on contraindications, timing and cost are in the complete guide to recent advances in neurosurgery.