Arachnoid cyst associated with painful tic convulsif.

Combined clinical presentation of hemifacial spasm and ipsilateral trigeminal neuralgia is known as painful tic convulsif (PTC). It is a rare condition and the most common cause is vascular compression. We report an arachnoid cyst of the posterior fossa that caused PTC in a 50-year-old woman. Her radiological evaluation revealed a median, well-circumscribed, cystic lesion of the posterior fossa suggestive of arachnoid cyst, pushing the cerebellum and brainstem anteriorly. Midline suboccipital craniotomy and marsupialization of cyst was performed with complete recovery of symptoms. To our knowledge, this is the first report of a retrocerebellar arachnoid cyst causing PTC.