Magnetic resonance imaging in acoustic neuroma diagnosis.

Magnetic resonance imaging (MRI) is capable of providing excellent images of the contents of the internal auditory canal and cerebellopontine angle. In order to determine whether MRI is comparable to air contrast computed tomography in the diagnosis of small acoustic neuromas, 44 patients with suspected retrocochlear disease were studied with both CT and MRI. Twenty-one lesions were identified successfully with MRI and CT. The size of the tumors ranged from 4 mm to 5 cm. In twenty-three nontumor patients the normal audiovestibular nerve bundles were well visualized. Air contrast CT, on the other hand, was falsely positive in two cases. The results of this study indicate that MRI is suitable as the primary anatomic investigation in patients suspected of having retrocochlear lesions. It has the advantages of being highly reliable as well as free of ionizing radiation and the need for invasive procedures. The expense of MRI compares favorably with that of combined intravenous and gas contrast CT.