[Clinical study in patients with perimesencephalic subarachnoid hemorrhage of unknown etiology]

We have recognized a characteristic distribution of cisternal blood in 10 (43%) of 23 patients with subarachnoid hemorrhage (SAH) of unknown etiology. On the initial CT examination undertaken within 48 hours of the onset, blood from 10 patients was found to be more densely distributed in the cisterns around the brainstem. In this study, clinical characteristics and CT findings in those 10 cases were carefully evaluated and the CT findings were compared to those of 416 patients with aneurysmal SAH (anterior circulation aneurysm 368 cases, posterior circulation aneurysm 48 cases). There were seven men and three women, with an age ranging from 39 to 64 years (average age, 50.6 years). The follow-up period ranged from 4 to 45 months (average follow-up period, 23 months). Neurological grade (WFNS) on admission was I in 9 cases and III in one case. None of the patients suffered symptomatic vasospasm, hydrocephalus or rebleeding. All the patients had favourable outcome and were categorized as good recovery according to the Glasgow Outcome Scale. In comparison with the cases of aneurysmal SAH, especially in comparison with 48 cases with SAH caused by posterior circulation aneurysm, 43 cases could be easily distinguished on CT. The other 5 cases showed almost the same pattern of SAH on CT, but 4 cases could be differentiated by either the extension of SAH to the interhemispheric fissure or the presence of intraventricular hemorrhage. Only one case could not be differentiated on CT. Thus SAH located only around the brainstem differs from aneurysmal SAH in its clinical course, and in distribution and severity of bleeding on CT. This could be recognized as a new clinical entity and could be called benign SAH.