Meningiomas of the cerebellopontine angle.

The majority of cerebellopontine angle tumors are acoustic neurinomas; however, 10% to 15% are meningiomas. Meningiomas are benign lesions that must be removed but may require surgical approaches different from those used for acoustic neurinomas. To determine if meningiomas could be distinguished from acoustic neurinomas clinically, findings in 20 patients who underwent removal of a meningioma were compared to those in 131 patients who had an acoustic neurinoma removed during the same period. We found that in patients with meningiomas the tumors frequently are large at presentation, the otologic symptoms and audiometric findings are less dramatic, and roentgenograms of the skull and tomograms of the petrous apex rarely show erosion of the internal auditory canal. Computerized tomography is the most useful method for differentiating a meningioma from a neurinoma: when a meningioma is present the characteristic finding is a broad-based mass aligned with the petrous ridge, not centered over the internal auditory canal.