Incidence and risk factors for multiple intracranial saccular aneurysms in patients with subarachnoid hemorrhage in Izumo City, Japan.

BACKGROUND: A community-based study was conducted to estimate the incidence rates of multiple aneurysms and to investigate the factors related to multiplicity.
METHOD: The subjects were 291 patients with ruptured saccular aneurysms treated between 1980 and 1998, in Izumo, Japan. There were 403 aneurysms in total, and 78 patients (27%) had multiple aneurysms.
FINDINGS: Both the crude and the age- and sex-adjusted annual incidence rates per 100,000 population for multiple and single aneurysms were five and 14 for all ages, respectively, and were higher in women than in men. The age-specific incidence rates of both multiple and single aneurysms showed a tendency to increase with age. Of the 190 patients who underwent four-vessel studies, 26% (49) had multiple aneurysms. The frequencies of multiple aneurysms in patients with ruptured aneurysms > or =10 and <10 mm in diameter were 41% and 21%, respectively (p = 0.0081). In patients with multiple aneurysms, the number of aneurysms was greater in those with large ruptured aneurysms, and the unruptured aneurysms tended to be larger in patients with large ruptured aneurysms. The size of the ruptured aneurysms was positively associated with multiplicity, whereas hypertension had an inverse association. Age, sex, aneurysm site and risk factors other than hypertension were not predictive.
CONCLUSIONS: This study is the first to provide annual incidence rates for multiple aneurysms in a defined population. It appears that multiplicity of aneurysms is associated with larger ruptured aneurysms and that patients with larger ruptured aneurysms have a higher number of aneurysms as well as larger unruptured aneurysms.