Hemifacial spasm caused by a cerebellopontine angle arachnoid cyst. Case report and literature review.

Arachnoid cysts involving the cerebellopontine angle are an unusual cause of hemifacial spasm. The case is reported of a 71-year old woman presenting with a right hemifacial spasm and an ipsilateral arachnoid cyst. Preoperative magnetic resonance imaging findings suggested a neurovascular compression caused by displacement of the facial-acoustic complex and the anterior inferior cerebellar artery by the cyst. Cyst excision and microvascular decompression of the facial nerve achieved permanent relief. The existing cases of arachnoid cysts causing hemifacial spasm are reviewed and the importance of a secondary neurovascular conflict identification and decompression in these cases is highlighted.