Hemifacial spasm caused by fusiform aneurysm at vertebral artery-posterior inferior cerebellar artery junction.

Hemifacial spasm induced by intracranial aneurysm is a rare clinical condition. A 45-year-old male patient presented with a 3-year history of progressive involuntary twitching movement on right face. On radiological study, a dilated vascular lesion compressing the brain stem was found at the junction of vertebral artery and posterior inferior cerebellar artery. On operative field, we found the posterior inferior cerebellar artery and the fusiform aneurysm compressing root exit zone of facial nerve. Microvascular decompression was performed and the facial symptom was relieved without complications.