Cerebellopontine angle masses: radiologic-pathologic correlation.

The cerebellopontine angle cistern is a cerebrospinal fluid-filled space bound by the pons, cerebellum, and petrous temporal bone. Masses in this region are readily identified on cross-sectional images. Differential diagnosis of masses in this region can be simplified by using an algorithmic approach that combines morphologic and enhancement characteristics with established demographic data. Schwannomas are enhancing, round masses, most commonly arising from the vestibular nerve near the porus acusticus and associated with enlargement of the internal auditory canal. Meningiomas are enhancing, oval or hemispheric lesions with a broad attachment to the tentorium or petrous dura mater. Congenital epidermoid inclusion cysts are nonenhancing masses that have undulating margins, molding their shape to conform to the adjacent structures. Aneurysms without significant internal thrombus have prominent flow voids on magnetic resonance images.