Cerebellopontine angle-petromastoid mass lesions: comparative study of diagnosis with MR imaging and CT.

Capabilities of computed tomography (CT) and magnetic resonance (MR) imaging in the diagnosis of cerebellopontine angle-petromastoid (CPA-PM) lesions were compared in 75 patients. CT and MR demonstrated 95.8% and 98.7% of the lesions, respectively. MR was often more helpful for characterization of neuromas, epidermoid cysts, exophytic gliomas, and vascular lesions, while CT was usually more informative for meningiomas, metastases, and tympanomastoid cholesteatomas. A specific diagnosis could be made with MR for most types of lesions through use of relaxation parameters and characteristic morphologic changes. Size, shape, location, and contour of the lesions, however, were generally more helpful for differential diagnosis than relaxation times. With the exception of metastatic lesions, cholesteatomas, and some meningiomas, MR was usually more helpful than CT in defining the full extent of the lesions and their relationships to contiguous structures. MR, because of its high accuracy in lesion detection, characterization, and localization, is a suitable primary diagnostic modality for evaluating patients with suspected CPA-PM lesions.