Nonaneurysmal subarachnoid hemorrhage: prevalence of perimesencephalic hemorrhage in a consecutive series.

The perimesencephalic type of nonaneurysmal subarachnoid hemorrhage (SAH) is a recently described clinical and radiological entity, with a good outcome. We carried out a retrospective analysis of 294 patients with subarachnoid hemorrhage, of whom 62 had a negative four-vessel angiography. We identified 20 cases with the typical computed tomographic (CT) pattern of perimesencephalic hemorrhage, in whom the prognosis was invariably good. However, five cases of aneurysmal subarachnoid hemorrhage had a more or less similar CT appearance: the diagnosis cannot be made on the CT image only and angiography remains mandatory. The use of bed rest, antifibrinolytics, and calcium antagonists is discussed.