**5. Outcomes**

Success rates of EVT vary from 50–90% in literature [52, 58]. Good outcomes are highest with up to about 90% in obstructive hydrocephalus series that includes aqueductal stenosis and

**Figure 6.** Flow void in T2-weighted sagittal MRI is clearly visible in the floor of the third ventricle after an ETV (black arrow).

tumors [23, 52]. However, communicating hydrocephalus cases have a rate of success about 50%. In patients who undergone shunt operations, ETV is still effective eliminating shunt dependency [59, 60]. Infants have worse outcomes in case of ETV according to literature. Failure rates vary between 20 and 50% [61]. Many authors recommend performing ETV in patients 2 years and older with their low success rates in infants [62, 63]. However, some authors indicate that ETV is still worth trying in these patients since the success rate is still considerable and a successful ETV provides long-term shunt independence [64, 65].

Radiographic features might be misleading as ventricular volume after EVD may not show an obvious change in the early preoperative period [66]. Early postoperative improvement and ventricular volume reduction are predictive values for the success of ETV as well as demonstrating flow void in the base of the third ventricle [67]. The patency of the ETV can be shown with flow void in T2-weighted images (**Figure 6**) and also with CSF flow cine MRI. Minor flow in the base of the third ventricle appears to be a bad prognostic factor for the patency of stoma [68].

Failure of ETV is in general due to the closure of fenestration in the third ventricle floor. The causes of the fenestration failure include the insufficient size of initial fenestration, reduced CSF reabsorption, arachnoid membranes in the prepontine cistern, hemorrhage obstructing fenestration, and late gliosis and postoperative infection. Failure rates can be as high as 50% in noncommunicating hydrocephalus series even with patent ventriculostomies [58].
