Incidence and prevalence of intracranial aneurysms and hemorrhage in Olmsted County, Minnesota, 1965 to 1995

Background: There are no previous reports of the incidence rate of intracranial saccular aneurysms in a defined population. Methods: Medical records of all residents of Olmsted County, MN, with a possible intracranial saccular aneurysm (IA) were reviewed. Incidence rates and prevalence of symptomatic and asymptomatic IAs, aneurysmal intracranial hemorrhage (ICH), and frequency of IA detection based on size and site were determined. Results: A total of 348 IAs were detected among 270 persons during the 31-year period from 1965 to 1995, including 188 symptomatic patients at presentation (166 with ICH). The age- and sex-adjusted incidence rate for IAs excluding asymptomatic autopsy cases was 9.0/100,000 person-years (P-Y; 95% CI, 7.8 to 10.2). The rate of detection in women (10.7/100,000 P-Y; 95% CI, 8.9 to 12.4) was higher than in men. The highest incidence of IA was among those age 55 to 64 years in men, and 65 to 74 years in women. The incidence rate of aneurysmal ICH was 6.9/100,000 P-Y (95% CI, 5.9 to 8.0). Aneurysms were seven times more likely to be detected in the anterior circulation, and this ratio was not altered significantly by age or gender. On January 1, 1990, the age- and sex-adjusted prevalence rate of identified IAs was 83.4/100,000 population (95% CI, 64.1 to 102.7). Conclusions: This study provides unique data on the population-based incidence and prevalence rates of IAs.