Computed tomography; the anatomic basis of the zone of diminished density surrounding meningiomas

Computed tomography of meningiomas often demonstrates a zone of diminished density surrounding the actual tumor. This zone may be related to widening of the subarachnoid space, cerebral edema, tissue necrosis, or demyelination. A case is presented in which the anatomic basis of the zone of diminished density was shown on pneumoencephalography and at surgery to be an enlarged subarachnoid space.