Walsh & Hoyt: Prevalence

The frequency with which ruptured and unruptured saccular aneurysms occur is the subject ofnumerous studies. Most of these studies are autopsy results from single medical centers. Stehbens (273) reviewed the results of 14 such studies and found that the prevalence of intracranial saccular aneurysms ranged from 0.29%, with an average of 2.4%. The variation in prevalence among studies is related to the nature and age distribution of the population studied and to the expertise and enthusiasm ofthe pathologist. Because most studies were performed retrospectively, it is possible that they underestimated the true prevalence of intracranial arterial aneurysms. Indeed Hassler suggested that aneurysms with diameters of 2 mm or less can be found in up to 17% of routine autopsy material and up to 60% in patients dying of SAH from a large aneurysm. On the other hand, angiographic retrospective studies give even lower numbers, with a prevalence between 0.5% and 1.1%. In addition, both autopsy and angiographic series are likely to be biased toward older patients, potentially increasing the apparent frequency. A correct estimate of the prevalence of aneurysms is obviously critical to setting up appropriate life tables. In a study from Olmsted county the incidence of symptomatic intracranial aneurysms has been estimated to be 9/100,000 person-years: higher in women than men. Cerebrovascular disease remains the third most frequent cause of death in the United States, and SAH may be associated with 525% of cases.