Idiopathic subarachnoid hemorrhage: is the perimesencephalic distribution that benign?

Introduction. - Idiopathic subarachnoid hemorrhage (iSAH) is generally recognized as benign especially if its distribution is perimesencephalic. In this study we assessed the complications following an iSAH and analyzed them in relation to the perimesencephalic or diffuse distribution of the hemorrhage. Method. - Retrospective study of 1,148 consecutive patients evaluated between January 1990 and April 2001 for iSAH documented by cerebral CT-scan with normal cerebral angiographic work-up. Results. - Of the eighty-seven patients (7.6%) presenting with iSAH, 52 presented with a perimesencephalic distribution, and 35 with a diffuse distribution. No statistically significant difference was observed between the two distributions with regards to complications following the hemorrhage, such as hydrocephalus, neurological deficits due to vasospasm, systemic effects and mortality. Fisher grade III was associated with an increased risk of complications. Conclusion. - Perimesencephalic iSAH is not exempt from complications. Morbidity and mortality in this group are comparable to those observed in diffuse iSAH. The Fisher grade is a predicting factor of complications for any given hemorrhage distribution.