[CT diagnosis of acoustic neuroma of cerebellopontine angle (analysis of 204 cases)].

The CT findings of 207 acoustic neuroma in cerebellopontine angle from 204 cases verified by operation and pathology were analysed. The following characteristics are found helpful to determine the nature of the tumor: (1) on plain scan the tumor either presents as a homogeneous isodense or slightly hypodense lesion, or as a hypodense and isodense mixed density lesion. (2) The margin of the lesion is not well defined before contrast enhancement, and it becomes clearly marginated with smooth or lobulated contour after enhancement. (3) The enhancement of a solid tumor is homogeneous or slightly inhomogeneous, but in a tumor with cystic change the enhancement is inhomogeneous or ring-like (single ring or multiple rings). (4) The center of tumor growth is located at the inner outlet of internal auditory canal. (5) The tumor attaches to the petrous bone with an acute angle. (6) The internal auditory canal is enlarged or eroded. In the differential diagnosis, usually meningioma should be considered, if the tumor is solid; and cholesteatoma and arachnoid cyst should be ruled out, if the tumor is mainly cystic.