Computerized tomography in subarachnoid hemorrhage: difference between patients with and without an aneurysm on angiography.

Fifty patients with spontaneous subarachnoid hemorrhage were investigated by both computerized tomography (CT), within 5 days of onset, and complete cerebral angiography. CT showed blood in the basal cisterns in 38 of the 42 patients with a demonstrable aneurysm, but in only 1 of 8 patients with a negative angiogram (p less than 0.001). This means that: (1) blood in the basal cisterns on CT almost certainly indicates a ruptured aneurysm, and (2) unexplained subarachnoid hemorrhages are unlikely to be caused by occult basal aneurysms.