Subarachnoid hemorrhage of unknown etiology

During a 10-year-period, 80 of 510 (16%) patients with primary subarachnoid hemorrhage (SAH) had negative angiographic studies. On admission, 70 of 80 patients (88%) were in grades I-II according to Hunt and Hess, 9 (11%) in grade III, and 1 (1%) in grade IV. The most frequent CT feature was preponderance of subarachnoid blood in the peripontine cistern as observed in 35 of 51 cases (69%) in whom blood was visible on CT. During hospitalization, 3 patients (4%) rebled, and 3 others (4%) had an infarction. However, in all of these complicated cases maximum hemorrhage was outside the peripontine cistern. Outcome after hospitalization as assessed by the Glasgow-Outcome-Scale (GOS) was favorable (GOS 1 and 2) in all patients who had maximum blood in the peripontine cistern, but only in 62% showing preponderance of blood outside the peripontine cistern, and 4 of them (25%) had died (GOS 5). These differences are statistically significant (p < 0.001). Long-term outcome of 56 patients as graded according to the Activities of Daily Living (ADL) system was favorable in 88% of cases with peripontine hemorrhage who returned to normal activities (ADL 1). At the same time, another patient with diffuse hemorrhage had died. Thus, overall mortality was 8.9% at a mean observation time of 5.5 years. In conclusion, SAH of unknown etiology generally has a good prognosis, although a nonneglegible percentage of patients have persistent minor side-effects. In our experience, maximum blood in the peripontine cistern particularly indicates a favorable outcome, since all patients with this CT pattern survived in a good condition.