Cooperative study of intracranial aneurysms and subarachnoid hemorrhage: a long-term prognostic study. III. Subarachnoid hemorrhage of undetermined etiology.

Among 6,638 cases reported to the Cooperative Study of Intracranial Aneurysms and Subarachnoid Hemorrhage were 477 cases in which the cause of hemorrhage could not be determined after carotid and vertebral angiography. These patients were followed up for up to 24 years after hemorrhage. Twenty patients were subsequently found to have an aneurysm or arteriovenous malformation missed by the first angiographic survey.

Cooperative study of intracranial aneurysms and subarachnoid hemorrhage: a long-term prognostic study. II. Ruptured intracranial aneurysms managed conservatively.

The late natural history of ruptured intracranial aneurysms was studied in 568 cases reported to the Cooperative Study of Intracranial Aneurysms and Subarachnoid Hemorrhage from 1958 to 1965. The patients had been selected for conservative management of their aneurysms at the time of diagnosis. A follow-up search in 1981 and 1982 revealed 378 known deaths; 40% had occurred within six months of hemorrhage.