**3.4 Consideration for success of ETV**

Patients, who have been previously shunted, are technically more difficult to perform ETV upon, because -

i.Less marked ventricular dilatation because of shunt assisted drainage

ii.A thicker ventricular floor

iii.Abnormal anatomy which is not an infrequent finding.

An ETV procedure may have to be abandoned in some cases for the following reasons –

i.Thick floor of the third ventricle

ii.Endoscopic view is obstructed by blood and cannot be cleared

iii.The basilar artery is very close or just under the planned site of fenestration.

iv.The anatomy is really unclear.

Despite all these, ETV has an overall success rate of approximately 75% after 3 years. Though the success depends not only on patient selection, but also on the experience of the surgeons. The results of ETV is better than shunting specially in patients with posterior fossa tumors [21]. In addition if the expenses are taken into account; ETV is superior to shunting [22].

Early failure of ETV can occur for mostly peroperative events such as

i.Bleeding around the fenestration site

ii.Unnoticed additional arachnoid membranes occluding the flow of CSF

iii.Inadequate size of the fenestration.

Late failure is the result of subsequent closure of the fenestration by gliotic tissue or arachnoid membrane. This problem is potentially serious because the failure can occur in a short period of time, may be unpredictable and presentation may be late due to a false sense of security. There are now several reports in the literature of death following late failure of ETV [23] and this remains a management problem. Tumor progression

and inadequate CSF absorption at the level of the arachnoid villi may result in early or late failure. A cohort of patients with open fenestrations who remained well for months, exhibits deterioration, the reasons of which are still not understood [24].

Procedure-related complications reported in the literature include bradycardia, hypothalamic dysfunction and hemorrhage from damage to arteries, ependymal veins, or the choroid plexus. The complications are divided into two main categories; short-term complications, which mostly resolve from intraoperative and technique-related, and long-term complications which occur at a much lower rate [25].
