For a study, researchers sought to investigate the incidence of unruptured intracranial aneurysms (UIAs) in a general population using a variety of definitions of the aneurysm. A total of 1862 adults between the ages of 40 and 84 were included in a population-based, cross-sectional study that utilized 3-dimensional time-of-flight 3 Tesla MR angiography to determine the size, kind, and location of UIAs. The size was determined by determining the greatest distance between any 2 sites in the aneurysm sac. Estimates of prevalence were made using diameter cutoffs of more than or equal to 1, 2, and 3 mm, both with and without the inclusion of extradural aneurysms. The prevalence of intradural saccular aneurysms of more than or equal to 2 mm was 6.6% overall (with a (95% CI 5.4% to 7.6%), 7.5% (95% CI 5.9% to 9.2%) in women and 5.5% (95% CI 4.1% to 7.2%) in men.  The overall prevalence of aneurysms ranged from 3.8% (95% CI 3.0% to 4.8%) for intradural aneurysms of more than or equal to 3 mm to 8.3% (95% CI 7.1% to 9.7%) when both intradural and extradural aneurysms 1 mm were included. This range was dependent on the definition of an aneurysm. The prevalence found in the study was significantly higher than that which had been previously observed in other Western populations. The significant prevalence of UIAs measuring less than 5 millimeters in diameter might indicate a lower risk of rupture than was previously predicted. The need for a consensus on radiological definitions of UIAs that were more robust and uniform had arisen.

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