Phase-contrast cine MRI revealing en valve mechanism in spontaneous third ventriculostomy: report of a case and literature review.

A 50-year-old epileptic woman affected by hydrocephalus due to aqueductal stenosis was admitted to the hospital because of headache, dysarthria, and mild lateral pulsion. Cranial computed tomography (CT) revealed left cerebellar hemorrhage. Subsequent magnetic resonance imaging (MRI) of the brain demonstrated an enlarged ventricular system unchanged from prior studies. Flow-sensitive phase-contrast (PC) cine magnetic resonance imaging showed flow absence through the aqueduct and flow pulsations through the third ventricle floor in systole and diastole, consistent with spontaneous third ventricle patency. On stationary tissue images, the third ventricle floor and the mamillary body were displaced downward at systole and upward at diastole. Stenosis of the cerebral aqueduct of Sylvius was also shown. Retrospective evaluation of the sagittal T2-weighted images disclosed flow void at the level of the third ventricle floor. On-off movements of the third ventricle floor could account for chronic hydrocephalus persistence by an en valve mechanism. Spontaneous third ventriculostomy (STV) was diagnosed on the basis of these findings. STV is a rare condition occurring in chronic obstructive hydrocephalus patients as a result of longstanding pulsations against the walls of the third ventricle, the floor in particular. We reviewed the literature to establish which imaging and clinical findings could improve the identification of STV in patients affected by obstructive hydrocephalus.