Periaqueductal tumor as a cause of late-onset aqueductal stenosis.

Localized periaqueductal tumors usually present as hydrocephalus, which is then thought to be late-onset congenital aqueductal narrowing. In the past, radiological investigations, including positive contrast ventriculography, pneumoencephalography and even contrast CT scanning, have frequently failed to show tumors in this region in the early stages. However, recent experience using MRI on patients with unexplained late-onset aqueductal stenosis has in some instances shown the presence of a localized periaqueductal tumor as the cause of obstruction of the aqueduct. Four patients are described with hydrocephalus secondary to presumed late-onset congenital aqueductal stenosis, all of whom were shown to have a periaqueductal tumor. One patient had been investigated with a pneumoencephalogram and positive contrast ventriculogram and CT with an early-generation scanner, but the tumor was diagnosed only at the time of autopsy. In one patient, the tumor was diagnosed by CT and also confirmed with MRI; a histologic diagnosis has been obtained. In two other patients, CT with and without contrast enhancement was negative and in one of these, a positive contrast ventriculogram was also negative, but the tumor was easily identified on MRI scans. In both of these patients, a histologic diagnosis was obtained by stereotactic biopsy. Periaqueductal tumors must be considered in the differential diagnosis of patients who present with late onset aqueductal occlusion and in such patients, MRI would appear to be the investigation of choice.