Object. The prevalence of unruptured cerebral aneurysms is unknown, but is estimated to be as high as 5%. The goal of this study was to determine the prevalence of asymptomatic incidental aneurysms.
Methods. The authors studied all cerebral arteriography reports produced at a single institution, the University of Virginia, between April 1969 and January 1980. A review of 3684 arteriograms demonstrated 24 cases of asymptomatic aneurysms, yielding a prevalence rate of 0.65%. The majority (67%) of the 24 patients harboring unruptured aneurysms were women. More than 90% of the unruptured aneurysms were located in the anterior circulation and in locations similar to those found in patients with ruptured aneurysms. Nearly 80% of the aneurysms were smaller than 1 cm in their greatest diameter. The frequency of asymmetrical unruptured aneurysms (0.6–1.5%) was constant throughout all relevant age ranges (35–84 years).
Conclusions. While keeping in mind appropriate caveats in extrapolating from these data, the prevalence rate of asymptomatic unruptured aneurysms found in the present study allows an estimation of the yearly rate of rupture of these lesions. The authors suggest that this yearly rate of rupture falls within the range of 1 to 2%.