Hemifacial spasm is characterized by intermittent, painless spasms of the facial muscles involving the facial nerve unilaterally. It may be limited to the upper or lower half of the face only. It usually begins as infrequent contractions of the orbicularis oculi, the muscle that wraps around the eye, and then increases in frequency until visual impairment occurs. This disorder can be associated with trigeminal neuralgia. It is more common in women, on the left side of the face, and usually presents in mid to late adulthood.

The most common cause of hemifacial spasm is vascular compression of the facial nerve at the root exit zone typically by the anterior inferior cerebellar artery (AICA). Other etiologies include tumor or cyst compression of the facial nerve and association with Bell’s palsy. 

Surgical management is generally preferred. Medical management may be attempted with local injection of botulinum toxin (Oculinum). Microvascular decompression (MVD) as detailed under trigeminal neuralgia is first-line. Unilateral hearing loss is the most common complication occurring in 13% of cases due to nerve injury. The risk may be reduced by intraoperative monitoring either via intraoperative brainstem auditory evoked potential (BAER) or direct VIII nerve monitoring. Other complications include facial weakness, which usually resolves on its own, gait disturbance, hoarseness or dysphagia due to nerve damage, and aseptic meningitis. Complete resolution of hemifacial spasm occurs in 85-93% of cases. Nine percent experience some relief while 6% do not. Nerve ablation surgery is an alternative to MVD but facial paralysis is a consequence.