Magnetic resonance imaging of acoustic schwannomas.

The magnetic resonance imaging (MRI) findings of 27 histologically proven acoustic schwannomas in 24 patients (13 men, 11 women, age 20-79 yr) are described in detail. Three patients had bilateral tumors. Twenty-two tumors (82%) had intra- and extracanalicular components, three tumors (11%) were limited to the internal auditory canal (IAC) and two tumors (7%) were limited to the cerebellopontine angle (CPA). The diameters of extracanalicular lesions in the CPA ranged from 12 to 50 mm, and most of them were round in shape. All IAC portions of CPA tumors had a funnel-shaped appearance on the axial images and short-club-shaped configuration on the coronal images. There was strong homogeneous contrast enhancement of the solid components in 12 tumors (44%) and heterogeneous enhancement in 15 tumors (56%). The cystic components of the tumors correlated well with the histologic features. All tumors could be demonstrated in their enterity by MRI. The "short-club sign", first described in this study, helped to confirm the intracanalicular component of acoustic schwannomas, which were usually found in the cerebellar cistern. The results of this study show that MRI is a sensitive imaging modality for the assessment of acoustic schwannomas located at the CPA or IAC, or in both regions. MRI is non-invasive and does not involve ionizing radiation. It should be considered the imaging examination of choice to evaluate patients with suspected acoustic schwannomas.