Vascular relationships of the vestibulocochlear nerve on magnetic resonance imaging.

Vascular compression of the vestibulocochlear (VIIIth) nerve may cause constant or recurrent positional vertigo, tinnitus, and/or hearing loss. At present the diagnosis is based upon history, physical findings, audiologic assessment, vestibular function testing, and auditory brainstem evoked responses. Delineation of the vascular and neural anatomy within the cerebellopontine angle (CPA) has not been part of the preoperative assessment. We recently treated a patient demonstrating the clinical features of this syndrome. A magnetic resonance imaging (MRI) study revealed a vascular loop of the anterior inferior cerebellar artery intimately associated with the VIIIth nerve at the porus acusticus. To better define the significance of this finding, we retrospectively reviewed the CPA neurovascular anatomy of 100 (200 sides) otherwise normal MRI scans performed for unrelated disorders. Vessels were identified on 59.9 percent of sides while nerves were seen on 40 percent of sides. Contact between vessel and nerve occurred on 12.5 percent of sides and when both nerve and vessels were seen concurrently, they were in contact 50 percent of the time. These findings may preclude the use of MRI as the definitive diagnostic test in the preoperative assessment of vascular VIIIth nerve compression.