Colloid cyst of the third ventricle in opposite sex, non-twin siblings

This report describes a colloid cyst of the third ventricle presenting in a 23-year-old woman. Subsequently, her brother presented with a similar colloid cyst also at 23 years of age. In both patients the cysts were successfully surgically removed. The cysts were examined by light microscopy utilizing immunohistochemical staining. The epithelial lining was essentially identical in both cases. Both cysts stained positively for cytokeratin and epithelial membrane antigen and negatively for S100, vimentin, carcinoembryonic antigen and glial fibrillary acidic protein. A genetic predisposition to this congenital condition may be present in some relatives of patients in whom colloid cysts have been detected.