Is endoscopic third ventriculostomy an internal shunt alone?

This study was made to define the mechanism of endoscopic third ventriculostomy (ETV) in the various forms of hydrocephalus.

One hundred and forty patients with various forms of hydrocephalus treated by ETV are reviewed. The series includes 75 cases (53.5%) of triventricular obstructive hydrocephalus (group 1), 20 (14.3%) with hydrocephalus following CSF infection or hemorrhage (group 2) and 45 (32.3%) with idiopathic normal pressure hydrocephalus (group 3). Factors which have been considered include type and etiology of the hydrocephalus, intraoperative evidence of downward and upward movement of the third ventricular floor after the stomy, patient outcome and rate of shunt-independent cases.

The overall rate of successful ETV was 79.3% (111/140 shunt-free patients). The success rate was 88% (66/75) in group 1, 60% (12/20) in group 2 and 73.4% (33/45) in group 3. The intraoperative finding of significant movement of the third ventricular floor after the stomy was evidenced in 121/140 cases (86.4%) and particularly in all cases of group 1, in 9/20 (45%) of group 2 and in 37/45 (82%) of group 3.

The relatively high rate of success of ETV in various forms of hydrocephalus and the intraoperative finding of mobility of the third ventricle floor after the stomy suggest that the first mechanism of the ETV is the restoration of pulsatility of the ventricular walls. This results in restoration of the CSF flow from the ventricular system into the subarachnoid spaces and normalization of the CSF dynamics. Accordingly, ETV is not only an internal shunt, but it primarily influences the capacity of the brain pulsatility to ensure CSF flow.