Gender Differences in Unruptured Intracranial Aneurysm Formation: Risk Factors and Characteristics

P151 The International Study of Unruptured Intracranial Aneurysms (ISUIA)Background and Purpose: There are few data available defining gender-based differences in intracranial aneurysm (UIA) risk factors and occurrence. The ISUIA provides a unique setting for evaluating these issues.Methods: Fifty-three centers in the ISUIA entered 5,669 patients with UIA. 1531 patients are part of a retrospective follow-up of unoperated UIA between 1970 and 1991. Another 4,138 comprise a prospective cohort. Half (58%) of this group are operated and 42% are unnoperated. Data were collected regarding history of subarachnoid hemorrhage (SAH) and factors including characteristics of the UIA, family history of stroke, cigarette smoking and many other demographic and medical history.Results: Combined analysis of these two cohorts revealed that women had a UIA 3 times more frequently than men (75% vs. 25%). Women had more multiple aneurysms than men did (52% vs. 42%; p=0.001). Women had a higher proportion of cavernous and internal carotid artery UIAs (46.5%) while the men more often had anterior and middle cerebral artery UIAs (54.5%), p<0.001. Women had an arteriovenous malformation less frequently than men did (1.6% vs. 3.7%; p=0.001). Cigarette use was less prevalent in women than men (69% vs. 76%; p=0.001) and alcohol use was lower in women than men (12.3% vs. 29.8%; p=0.001). Women were more likely to be hypertensive, (40.3% vs. 36.2%; p=0.02) and had vascular headache more than men, (27.3% vs. 16.9%; p=0.001). Age at diagnosis of UIA and family history of aneurysm, SAH, or indeterminate hemorrhages were similar for men and women. Women in Group 1 (UIA, no prior SAH) more often used oral contraceptives and estrogen replacement therapy than women in Group 2 (UIA, prior SAH from a second aneurysm). Also, Group 1 women more often had a history of hypertension. Women in Group 2 used cigarettes, alcohol and stimulants and had a history of vascular headache more often.Conclusions: Women are more likely to harbor UIA than men. Aneurysm characteristics such as location and multiplicity may differ, between genders. Selected risk factors for aneurysm formation may explain these.