MR of aqueductal stenosis: evidence of a broad spectrum of tectal distortion.

The MR scans of 18 patients with nontumoral aqueductal stenosis and six patients with neoplastic stenosis of the aqueduct were reviewed in order to document and understand the variable appearance of the aqueduct and periaqueductal region on MR. The mesencephalic tectum is often distorted in patients with benign aqueductal narrowing. This distortion results in a number of different MR appearances ranging from an elongated and thin to a short and broad tectum. When compressed by a dilated suprapineal recess, the distorted tectum is sometimes difficult to differentiate from the bulbous enlargement caused by a tectal glioma. Patients in whom distortion of the tectum is the result of hydrocephalus and aqueductal stenosis should be recognized to avoid unnecessary diagnostic procedures and misdiagnosis.