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Original research
Prevalence of unruptured intracranial aneurysms: impact of different definitions – the Tromsø Study


Background Management of incidental unruptured intracranial aneurysms (UIAs) remains challenging and depends on their risk of rupture, estimated from the assumed prevalence of aneurysms and the incidence of aneurysmal subarachnoid haemorrhage. Reported prevalence varies, and consistent criteria for definition of UIAs are lacking. We aimed to study the prevalence of UIAs in a general population according to different definitions of aneurysm.

Methods Cross-sectional population-based study using 3-dimensional time-of-flight 3 Tesla MR angiography to identify size, type and location of UIAs in 1862 adults aged 40–84 years. Size was measured as the maximal distance between any two points in the aneurysm sac. Prevalence was estimated for different diameter cutoffs (≥1, 2 and 3 mm) with and without inclusion of extradural aneurysms.

Results The overall prevalence of intradural saccular aneurysms ≥2 mm was 6.6% (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. Depending on the definition of an aneurysm, the overall prevalence ranged from 3.8% (95% CI 3.0% to 4.8%) for intradural aneurysms ≥3 mm to 8.3% (95% CI 7.1% to 9.7%) when both intradural and extradural aneurysms ≥1 mm were included.

Conclusion Prevalence in this study was higher than previously observed in other Western populations and was substantially influenced by definitions according to size and extradural or intradural location. The high prevalence of UIAs sized <5 mm may suggest lower rupture risk than previously estimated. Consensus on more robust and consistent radiological definitions of UIAs is warranted.


Data availability statement

Data are available on reasonable request. Data may be obtained from a third party and are not publicly available. Data availability are restricted due to their sensitive nature. Deidentified data can be obtained by application to the Tromsø Study, please contact for details.

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