Retroclival arachnoid cyst with hemifacial spasm.

Arachnoid cysts are rare lesions occurring anywhere in the cerebrospinal axis. The sylvian fissure remains the most favoured site for their occurrence, followed by cerebellopontine angle, suprasellar, and quadrigeminal cisterns. Retroclival arachnoid cysts are very rare. We report a retroclival arachnoid cyst with bilateral cerebellopontine angle extensions with hemifacial spasm in a 26-year-old woman. The patient underwent surgery and her hemifacial spasm improved.