[Clinical analysis of etiology of spontaneous subarachnoid hemorrhage diagnosed by computed tomography].

In 575 cases with subarachnoid hemorrhage (SAH) diagnosed by computed tomography (CT) scan, four vessel cerebral angiography was performed several times at more than two-week intervals to investigate a source of the hemorrhage. The first four-vessel study on admission revealed 530 cases (92.2%) of ruptured cerebral aneurysms, four (0.7%) of ruptured arteriovenous malformation, 25 (4.3%) of unknown etiology. Repeated four vessel study showed eight (32.0%) aneurysms among 25 cases whose first studies were negative. Six of the eight cases had aneurysms in the vertebro-basilar system. In 11 cases, repeated four-vessel study failed to detect the hemorrhagic source; and no generalized diseases were noted. One of them had recurrence of SAH 19 months after the onset of the initial one. The patient was underwent operation, which showed thrombosed ruptured aneurysm. Our present investigation demonstrated that ruptured aneurysm was responsible for 94.8% of all 575 cases of SAH detected by CT scans and 10 cases (1.7%) were diagnosed as cases of SAH of unknown etiology.