Hemifacial spasm caused by a tortuous vertebral artery: MR demonstration.

Hemifacial spasm is a symptom complex comprising involuntary, painless spasms of the orbicularis muscle that may progress to involve all facial muscles. It is frequently the result of compression of the facial nerve at its root exit zone from the brain stem by vascular loops or aneurysms of the posterior inferior cerebellar artery, anterior inferior cerebellar artery, vertebral artery, or cochlear artery. Coronal and axial T1-weighted images clearly depict the course of the facial nerve from the brain stem to the internal auditory canal and its relation to the vertebrobasilar system. This case demonstrates the magnetic resonance appearance of a tortuous vertebral artery and its relationship to the facial nerve in a patient with long standing hemifacial spasm.