Home> Blogs > Neurosurgery > Endoscopic Third Ventriculostomy: an Innovation in Neurosurgery
Endoscopic Third Ventriculostomy: an Innovation in Neurosurgery
Hydrocephalus means ‘water in the brain’, but the term denotes an abnormal increase in the water content within the brain’s cavities. This clear fluid, called ‘cerebrospinal fluid or CSF’, is produced within cavities of the brain called ‘ventricles’, circulates within various channels, escapes the ventricles through small holes, bathes the brain surface from outside and gets absorbed in the large veins outside the brain by a unique system. CSF is essential for brain functioning, and production and absorption are matched.
Suppose the circulation or absorption of CSF gets hampered for some reason. In that case, it leads to the accumulation of fluid inside the brain cavities, leading to enlargement of the cavities and pressure on the brain tissue, damaging brain cells, leading to potentially harmful effects – ranging from just headaches to head enlargement, physical incapacity, mental retardation, blindness and death.
Hydrocephalus is known from ancient times and is supposed to occur in one in 200 live births. Hydrocephalus has many causes dependent on the age of the patient
Causes in the pediatric population
congenital (due to malformations like aqueductal stenosis or due to intrauterine bleeding in the brain
acquired (a complication of trauma, infection or tumour).
In adults, the causes are
tumours
late onset aqueductal stenosis
consequences of trauma
bleed, infection and normal pressure hydrocephalus.
As far as management is concerned, hydrocephalus is classified according to the mechanism which leads to the accumulation of fluid in the brain cavities –
Obstructive hydrocephalus – a structural lesion causes hindrance to the flow of CSF, blocking it within the ventricular system, e.g. aqueductal stenosis or a tumour tentorial notch preventing the CSF flow from IIIrd to the fourth ventricle.
Communicating hydrocephalus
Sometimes, a third, mixed type, is proposed when the mechanism is poorly understood or incompletely understood.
Surgeries for relief from this condition are aimed at fluid drainage and have been performed for over 100 years. They can be grossly divided into external diversion procedures, called shunts (where the fluid is taken out of the head with the help of a tube and released into the abdominal cavity or blood) or internal diversion procedures like ventriculostomy, where ‘stoma’ or opening is created for draining the trapped fluid inside the ventricle to the exterior of the brain, to be absorbed by the natural mechanism.
This opening could be done with major open surgery (as was done long ago) or with the help of an endoscope, called endoscopic third ventriculostomy, or ETV. This ETV surgery is ideal for most cases of obstructive hydrocephalus and will be discussed in detail. ETV aims to form a new pathway for ‘internal’ (intracranial) drainage of CSF, thus bypassing the ‘obstruction’; hence, it is more physiological as against ‘external’ drainage, shunt surgery.
One of the great pioneers of neurosurgery, Dr. Walter Dandy, conceived the idea of ventriculostomy in the 1920s for the management of hydrocephalus. However, it fell out of favour due to high complications, mainly because the instrumentation was underdeveloped.
Advances in optical technology, micro-instrumentation, high-resolution imaging, and neuroimaging, together with a rising interest in minimally invasive techniques, have resulted in the re-establishment of modern neuro endoscopy and led to a resurgence of Endoscopic Third Ventriculostomy (ETV).
Today, ETV is the most commonly practised cranial neuroendoscopic procedure.
Endoscopic ventriculostomy in action: The diagram on the left shows how aqueductal stenosis causes hydrocephalus, while the right shows ETV creating an alternate channel in the floor of the third ventricle.
The surgeon must first decide which cases are subject to ETV and which are subject to shunt surgery. He should have sound knowledge of the pooled data (evidence base) and be able to apply it to the given case by studying various details (clinical and radiological) of the specific case, using his personal experience and judgment in that given case.
Factors affecting success:
Mechanism – obstructive or not
AGE – Concept of Cranial maturation of CSF absorption: – success rate of ETV after 2 years of age is excellent. This is supposedly due to the immaturity of the mechanisms responsible for the absorption of the fluid at a very young age.
In the pediatric population, obstructive hydrocephalus due to aqueductal stenosis and tumours has documented a success rate.
ETV is more successfully employed in various adult cases of hydrocephalus, such as secondary obstructive hydrocephalus (due to a brain tumour compressing CSF channels, e.g., Pineal tumours, tectal gliomas, posterior fossa tumours, cerebellar infarct), and where removal of the tumour is not feasible. Success rates are up to 90%.
The late-onset idiopathic aqueductal stenosis (LIAS) success rate is > 80% in adults.
Anatomical details—practical issues influencing operative steps that need to be studied on imaging, like the size of the foramen of Monroe, the floor of the third ventricle, the position of the basilar artery, etc.
ETV is sometimes also undertaken as conversion of a shunt in a patient who was treated for hydrocephalus as a child:- either the child was less than a year old at the time of surgery or simply because ETV was unavailable. Now, the patient has presented with shunt dysfunction.
Preparation before surgery :
Besides history and examination, careful imaging study is vital in pre-operative evaluation. MRI is the imaging of choice. High-resolution MRI also shows small obstructive lesions and blood products or other debris. Sagittal kinematic CINE and phase-contrast MRI can identify the absence of flow through the aqueduct.
Why ETV? Is there evidence of supremacy for ETV?
ETV is promoted as a ‘more physiological surgery’ that offers a ‘one-time solution’ compared with the shunt surgery option. The idea of ETV is appealing as it makes the patient ‘implant free’, and the surgery is an elegant technical challenge (viz., not a resident’s job or not everyone else’s). The current consensus states that the incidence of acute complications may be higher with ETV. Still, a successful ETV eliminates the need for long-term shunting, its attendant morbidity, suffering and the cost that comes with shunt failures.
At the same time, it is folly to think that ETV is a ‘cure’ for every case of hydrocephalus. Each surgeon wants to give his patient a permanent solution with minimum risk and complications. Hence, careful patient selection is the key to maximising the chance of success and minimising the complication rate.
Technique and instrumentation
Remember: Minimally invasive ≠ minor surgery! It should only be undertaken in fully staffed and equipped neurosurgical operating rooms by surgeons prepared to tackle its complications and proceed to an open operation if necessary. A postoperative neuro-intensive care unit (ICU) is a must.
The principle of surgery is to create an internal fistula (passage) between the ventricular system and the area around the base of the brain, called basal subarachnoid spaces, to drain out the fluid trapped inside the ventricles into the subarachnoid system.
The surgeon should be able to appreciate the variations, abnormalities, and distortions caused by hydrocephalus/lesions and guide the endoscope properly.
The endoscope gives a very high-resolution but monocular two-dimensional (2-D) view, which is further ’tilted’ (if a 30` camera scope is used). So, the surgeon needs to become very good at hand-eye coordination.
Surgical steps are simplified for the reader:
In contrast to open surgery, in endoscopy, only a tiny hole is made into the skull, through which the endoscope is inserted into the brain’s ventricles. It is navigated from the lateral ventricle into the smaller third ventricle, advanced to the appropriate location at the third ventricle floor, and the fistula or stoma is made with the help of special instruments.
Comparison of a binocular, 3D cadaveric specimen (left) with a monocular, 2D endoscopic intraoperative view of the floor of the third ventricle. The star ‘*’ indicates an ideal site for fenestration.
Perforation is then made in the thinned floor of the third ventricle, allowing cerebrospinal fluid (CSF) to egress out of the blocked ventricular system and into the CSF space outside, but at the base of the brain (a standard CSF space).
Thus, a fistula or stoma (opening) is created and dilated sufficiently. CSF flow is confirmed by observing the to-and-fro flapping movements of the stoma’s lips.
Once the stoma’s patency is confirmed, the scope is withdrawn, and the incision is closed. The patient is usually observed in the ICU overnight.
Over the last 15 years, we have performed nearly 100 ETV surgeries, and our results are comparable to those of any top neurosurgical centre worldwide. Our results are even better with experience, better case selection, and minor but essential technique modifications.
Innovations in neurosurgery should ultimately lead to a better quality of life for the patient and, especially for children, a “level of reassurance and peace of mind” for their parents.
FAQs
What is an endoscopic third ventriculostomy (ETV)?
ETV is a surgical procedure to treat hydrocephalus by creating a pathway for cerebrospinal fluid to bypass obstructions.
Who is a candidate for endoscopic third ventriculostomy?
ETV is often suitable for patients with obstructive hydrocephalus but may not be effective for all types.
How is ETV different from shunt surgery?
ETV does not require an implant, unlike shunt surgery, which uses a tube to divert fluid away from the brain.
What are the risks of ETV?
Risks include bleeding, infection, and the potential need for additional procedures if ETV is unsuccessful.
What is the recovery like after ETV?
Recovery is typically quicker than shunt surgery, with many patients resuming normal activities within weeks.
