Trapped fourth ventricle in coccidioidal meningitis.

A 4-year-old girl with known coccidioidal meningitis developed posterior fossa signs. CT scanning revealed a large fourth ventricle. Injection of contrast medium into the lateral ventricles revealed free flow into the fourth ventricle, and injection into the fourth ventricle revealed no flow into the aqueduct or third ventricle. The posterior fossa signs cleared after shunting of the fourth ventricle. A one-way aqueductal valve resulting from the ventricular inflammation is hypothesized.