Spontaneous subarachnoid hemorrhage (SAH) of unknown cause is not rare even though modern neuroradiological technique has greatly reduced its incidence. Between March 1976 and October 1981, 55 patients were admitted for treatment of SAH whose underlying source could not be found. Each patient had severe headache of sudden onset, a characteristic manifestation of SAH, and SAH was confirmed by the presence of blood-stained or xanthochromic lumbar CSF. Panangiography (three- or four-vessel study) was negative, and computed tomography (CT) disclosed no presence of intracerebral hematoma, recent infarction, or tumor. Hemorrhagic diathesis was excluded. Repeat panangiography was performed in 24 cases and was negative.
The average age at the time of onset was 48.3 years in the males (n = 30) and 54.0 years in the females (n = 25). The symptoms were usually relatively mild; three-fourths of the patients presented no focal neurological findings. Subarachnoid clot on CT was less than that noted in patients with ruptured aneurysms; subarachnoid clot was found in only 14 patients (25%) on admission. In no case was there a further episode of SAH during the average admission period of 4 weeks. The follow-up period ranged from 6 months to 5 years and 11 months. Forty-seven patients (85%) returned to their former employment. No patient experienced a second SAH, except for one female who suddenly died 3 years after discharge, possibly because of SAH.
