By: Justin F. Fraser, MD
Previous studies examining the prevalence of unruptured intracranial aneurysms (UIAs) report a range of 0.8-8.4%. Given this high variance, Harada et al. (Acta Neurochir, August 2013[online]) conducted a review of healthy asymptomatic adult patients who underwent MRA over 2 years in Japan. Of the 8696 patients included, the overall UIA prevalence was 3.2%, with increasing prevalence with age. The mean size at diagnosis was 3.4 +/- 2.0mm, with 84.5% of aneurysms less than 5 mm. The prevalence was higher in women (4.4%) than men (2.5%, OR 1.81) and internal carotid artery aneurysms were more common in women while middle cerebral and anterior communicating were more common in men (p<0.001). The authors note potential selection bias in their report, particularly socioeconomic factors (asymptomatic patients undergo the test at their own expense) and geographic restrictions (the study was conducted in a single prefecture). An additional limitation was the lack of information regarding risk factors (eg. smoking, hypertension, family history). Nevertheless, this study provides insight into the modern prevalence of UIAs. If UIAs are present in 3.2% of the population, support for rupture-prediction models is necessary in order to determine the role for treatment in the asymptomatic patient.