Localized cystic subdural hygroma: case report.

We report a new variant of subdural hygroma previously undocumented in the literature. A 29-year-old man had a skull mass and a progressive headache of 6 to 7 years duration. He was involved in a car crash 8 years earlier and had an unrecognized skull fracture. During surgery the lesion was found to be a localized, cystic subdural hygroma communicating with the subarachnoid space through a narrow opening. This lesion is unique because: (1) the subdural hygroma was limited by an adhesion between the dura and the arachnoid; (2) the actual communication between the subdural hygroma and the subarachnoid space was clearly identified; and (3) localized bulging of the skull is exceptional for a subdural hygroma. Differentiation from more common cystic lesions such as congenital arachnoid cysts, traumatic arachnoid cysts, intradiploic arachnoid cysts, and chronic subdural hematomas is discussed.