Prevalence and Risk of Rupture of Intracranial Aneurysms

Background and Purpose —The estimates on the prevalence and the risk of rupture of intracranial saccular aneurysms vary widely between studies. We conducted a systematic review on prevalence and risk of rupture of intracranial aneurysms and classified the data according to study design, study population, and aneurysm characteristics. Methods —We searched for studies published between 1955 and 1996 by means of a MEDLINE search and a cumulative review of the reference lists of all relevant publications. Two authors independently assessed eligibility of all studies and extracted data on study design and on numbers and characteristics of patients and aneurysms. Results —For data on prevalence we found 23 studies, totalling 56 304 patients; 6685 (12%) of these patients were from 15 angiography studies. Prevalence was 0.4% (95% confidence interval, 0.4% to 0.5%) in retrospective autopsy studies, 3.6% (3.1 to 4.1) for prospective autopsy studies, 3.7% (3.0 to 4.4) in retrospective angiography studies, and 6.0% (5.3 to 6.8) in prospective angiography studies. For adults without specific risk factors, the prevalence was 2.3% (1.7 to 3.1); it tended to increase with age. The prevalence was higher in patients with autosomal dominant polycystic kidney disease (relative risk [RR], 4.4 [2.7 to 7.2]), a familial predisposition (RR, 4.0 [2.7 to 6.0]), or atherosclerosis (RR, 2.3 [1.7 to 3.1]). Only 8% (5 to 11) of the aneurysms were >10 mm. For the risk of rupture, we found nine studies, totalling 3907 patient-years. The overall risk per year was 1.9% (1.5 to 2.4); for aneurysms =10 mm, the annual risk was 0.7% (0.5 to 1.0). The risk was higher in women (RR, 2.1[1.1 to 3.9]) and for aneurysms that were symptomatic (RR, 8.3 [4.0 to 17]), >10 mm (RR, 5.5 [3.3 to 9.4]), or in the posterior circulation (RR, 4.1 [1.5 to 11]). Conclusions —Data on prevalence and risk of rupture vary considerably according to study design, study population, and aneurysm characteristics. If all available evidence with inherent overestimation and underestimation is taken together, for adults without risk factors for subarachnoid hemorrhage, aneurysms are found in approximately 2%. The vast majority of these aneurysms are small (=10 mm) and have an annual risk of rupture of approximately 0.7%.