Elastance correlates with outcome after endoscopic third ventriculostomy in adults with hydrocephalus caused by primary aqueductal stenosis

OBJECTIVE: To study prospectively the correlation between clinical outcome after endoscopic third ventriculostomy (ETV) and resistance to the outflow of cerebrospinal fluid (R-out) and elastance in adults with hydrocephalus caused by primary aqueductal stenosis (AS). METHODS: R-out and elastance were measured in the subarachnoid space and intraventricularly before ETV in 15 consecutive patients. Three months after the ETV, the clinical effect was evaluated by standardized indices, and R-out and elastance were measured. If symptoms persisted and the ETV was patent, shunt surgery was offered. The effect of the shunt operation and R-out were measured after 3 months. RESULTS: Four patients experienced excellent improvement, six improved slightly, and five had unchanged or deteriorated symptoms after ETV. R-out before ETV did not correlate with outcome. R-out decreased after ETV with correlation to the clinical effect; in the six patients who had shunt surgery, R-out decreased further. High preoperative elastance correlated strongly with a good outcome and reduction of ventricle size. Elastance did not change after ETV. CONCLUSION: R-out intraventricularly and in the subarachnoid space could not predict the outcome of the ETV, but the reduction in R-out correlated positively with clinical improvement. Preoperative elastance correlated positively with clinical improvement, and elastance was unchanged after ETV. Clinical improvement correlated positively with reduction in ventricle size.