[Cerebellopontine angle epithelial cyst presenting as hemifacial spasm].

A rare case of cerebellopontine angle epithelial cyst presenting as hemifacial spasm is reported. The patient was a 35-year-old man with right hemifacial spasm of 2 months duration. A preoperative CT scan showed a well-demarcated low density area in the right cerebellopontine angle. The cyst was totally excised under an operating microscope. The postoperative course was uneventful, and the right hemifacial spasm resolved immediately. Histologically, the cyst wall was composed of a stratified epithelial lining composed of non-ciliated cuboidal or squamous cells. Ultrastructurally, the epithelial layer consisted of two types of cells: non-ciliated cells with microvilli coated with electron-dense material, and basally located cells with tonofilaments and well-developed desmosomes. The latter type of cells appear identical to the basal cells characteristically seen in the upper respiratory tract and the gastrointestinal tract. This findings suggest that the cyst was of endodermal origin rather than neuroectodermal origin.