Arachnoid cyst in the quadrigeminal cistern.

Two cases of arachnoid cysts in the quadrigeminal cistern are presented, and one occurred in an adult. Signs and symptoms of increased intracranial pressure were noted, and obstructive hydrocephalus was shown by computed tomography scans in both cases. Arachnoid cysts in the quadrigeminal cistern have rarely been reported, especially in adults. The definition, classification, and etiology of arachnoid cyst are still confused in the literature, and various terms have also been used to indicate this particular location of cyst. In this study, these confusing problems are reviewed, and the usefulness of metrizamide computed tomographic cisternography is emphasized as a noninvasive method of diagnosis.