ENDOSCOPIC THIRD VENTRICULOSTOMY : An innovation in neurosurgery
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 neuroendoscopy and has led to resurgence of Endoscopic Third Ventriculostomy (ETV).
Today, ETV is the most commonly practiced cranial neuroendoscopic procedure.
Endoscopic ventriculostomy in action: Diagram on the left shows how aqueductal stenosis causes hydrocephalus, while on the right shows creation of alternate channel in the floor of third ventricle by ETV.
The surgeon first needs to decide which cases to subject for ETV and which for 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 immaturity of the mechanisms responsible for absorption of the fluid at very young age.
In the pediatric population obstructive hydrocephalus due to aqueductal stenosis and tumours have documented good success rate.
ETV is more successfully employed in various adult cases of hydrocephalus like secondary obstructive hydrocephalus (due to brain tumour compressing on CSF channels e.g. Pineal tumors, tectal gliomas, posterior fossa tumors, cerebellar infarct) and where removal of the tumour is not feasible. Success rates are up to 90%.
In adults, the in the late-onset idiopathic aqueductal stenosis (LIAS) success rate is > 80%.
Anatomical details - practical issues influencing operative steps which need to be studied on imaging, like size of foramen of Monroe, floor of IIIrd ventricle, position of 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 at the time of surgery or simply because ETV was unavailable and now the patient has presented with shunt dysfunction.
Preparation before surgery :
Apart from history and examination, careful study of the imaging is vital in pre-operative evaluation. MRI is the imaging of choice. High resolution MRI also shows small obstructive lesions, presence of blood products or other debris. Sagittal kinematic CINE, phase-contrast MRI can identify absence of flow through the aqueduct.
Why ETV? Is there evidence of supremacy for ETV?
ETV is promoted as a 'more physiological surgery' which offers a 'one time solution' as compared with the shunt surgery option. The very idea of ETV is of course appealing as it makes patient 'implant free' and the surgery is itself an elegant technical challenge (viz. not a resident's job or not that everyone does). The current consensus states that the incidence of acute complications may be a bit higher with ETV, but a successful ETV eliminates the need long-term shunting, its attendant morbidity, suffering and the cost that comes with shunt failures. At the same time it is a folly to think that ETV is 'cure' for each and every case of hydrocephalus. Each surgeon would like to give his patient a permanent solution with minimum risk and complications, and hence, careful patient selection is the key for maximizing the chance of success and minimizing the complication rate.