[Non-neuroectodermal epithelial cyst in the middle cranial fossa associated with unilateral exophthalmos]

A rare case of unilateral exophthalmos caused by an epithelial cyst in the middle cranial fossa was reported. A 42-year-old man had a proptosis of sudden onset in the left eye. Ophthalmological examinations revealed a proptosis of 3mm, contraction of the lower visual field and a bow tie atrophy of the optic disc in the left. Plain skull X-P, CT scan and MRI disclosed a cystic lesion in the left middle fossa, resulting in the enlargement of the superior orbital fissure of the same side. Metrizamide CT cisternography showed the cyst had no communication with the subarachnoid spaces. The cyst, removed surgically, was located in the epidural region of the middle fossa and was about 4cm in diameter, containing yellowish turbid fluid and fat-like floating substance. Histologically, the cyst was composed of collagenous connective tissue, lined with pseudostratified columnar to cuboidal epithelia. Small cells with a high nuclear to cytoplasmic ratio, considered as basal cells or reserve cells, were often seen in the basal layer. Ciliated and secretory cells were rarely observed in the superficial layer. Neither stratified squamous epithelium nor adamantinomatous structure was seen. Immunohistochemical studies revealed that the lining epithelium was strongly positive for keratin (wide spectrum), but negative for vimentin, S-100, neuron specific enolase or glial fibrillary acidic protein. These staining characters were different from those of neuroectodermal cells including ependymal cells and choroidal cells which are usually vimentin- and S-100-positive. Morphologically, the lining epithelium resembled respiratory or alimentary tract epithelium, suggesting that the cyst might be derived from non-neuroectodermal ectoderm or endoderm.(ABSTRACT TRUNCATED AT 250 WORDS)