Tight Sylvian cisterns associated with hyperdense areas mimicking subarachnoid hemorrhage on computed tomography--four case reports.

Four patients with supratentorial mass lesions (two chronic subdural hematomas, one acute epidural hematoma, and one acute subdural hematoma) showed hyperdense sylvian cisterns on computed tomography (CT). Association of subarachnoid hemorrhage was suspected initially, but was excluded by intraoperative observation or postoperative lumbar puncture. CT showed disappearance of the hyperdense areas just after evacuation of the mass lesions. The hyperdense areas are probably a result of the partial volume phenomenon or concentrations of calcium deposits rather than abnormally high hematocrit levels, which were not found in these patients.