Special features of familial intracranial aneurysms: report of 215 familial aneurysms.

FAMILIAL INTRACRANIAL ANEURYSMS (FIAs) were compared with nonfamilial aneurysms (non-FIAs); the study group from east Finland included 167 family members from 85 families with FIAs. In every family, there has been two or more proven cases of subarachnoid hemorrhages among first-degree family members. Two-hundred and fifteen FIAs were found. The patients with FIAs were younger, and their aneurysms were smaller. Half of the FIAs were on the middle cerebral artery (n = 106 of 215), preferentially on the right side. Nearly one-third of the ruptured FIAs were smaller than 6 mm, and more than 80% of the aneurysms were under 14 mm in diameter. There were no significant differences between the frequency of aneurysms at mirror sites in FIA and non-FIA groups. Among siblings with FIAs, the frequency of pairs with age at onset within 10 years of each other was more than twice that expected from randomly selected pairs in the non-FIA group.