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Hemifacial spasm is characterised by unilateral involuntary contractions of muscles innervated by the seventh cranial nerve. It usually has a fluctuating course, with spasms that may be triggered by several factors such as stress, bright light, and swallowing. Its most probable aetiology is the compression of the seventh nerve at its anterior caudal root exit zone by vascular loops of the posterior inferior cerebellar artery, anterior inferior cerebellar artery, or vertebral artery. We report on a 67 year old patient who had had a right side hemifacial spasm for the previous three months. A neurological examination was otherwise normal. Cerebral 1.5 T MRI with T2 weighted sequences (see figure) showed a vascular loop, probably a branch of the anterior inferior cerebellar artery (arrow), which penetrated into the right internal auditory canal, compressing the seventh cranial nerve. The patient improved after treatment with local botulinum toxin injections. Neuroimaging studies of patients with hemifacial spasm have shown compression of the seventh cranial nerve by vascular structures in its exit zone from the brain stem1but not in its peripheral course, as shown in our patient.
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