Prevalence of unruptured intracranial aneurysms according to comorbidities, risk factors, country, and time period: a systematic review and meta-analysis

Background The incidence of aneurysmal subarachnoid haemorrhage declined between 1980 and 2010, which coincided with a decline in smoking and prevalence of hypertension. We aimed to investigate whether the decrease in subarachnoid haemorrhage incidence is paralleled by declines in unruptured intracranial aneurysm (UIA) prevalence. Methods For this systematic review and meta-analysis, we searched Embase, PubMed, and Web of Science for articles published in any language from Jan 1, 2011 to Dec 31, 2025, and reassessed 68 articles published before March 1, 2011 from a 2011 systematic review and meta-analysis. Articles were eligible for inclusion if they used a cross-sectional or case–control design and provided the crude number of participants and those with UIA. We only included studies reporting numbers of UIA separately from ruptured aneurysms and with ten or more patients. Summary data were independently extracted by JD with AZ or CB and conflicts were resolved by GJER. The primary outcome was proportion of participants with UIA. Relative to a hypothetical reference population (mean age 50 years, 50% women, and no comorbidities), age and/or sex-adjusted prevalence ratios (PRs) for regions, comorbidities, and risk ratios (RRs) for female sex, smoking, and hypertension were estimated using generalised linear mixed models. A time trend analysis was done by binomial meta regression using the mid-year of data acquisition. We assessed the certainty of evidence using GRADE. The study was registered with PROSPERO, number CRD420261296728. Findings Our search screened 4708 studies. 67 reassessed and 95 newly identified articles, reporting on 316 131 participants and 11 822 people with UIAs, were included in our meta-analysis. In the reference population, the estimated prevalence of UIAs was 3·9% (95% CI 3·0–5·1). The prevalence of UIAs in individuals with atherosclerosis was 5·5% (4·7–6·4; 2229 of 40970 participants) and the adjusted PR was 1·3 (95% CI 0·8–2·0) compared with the reference population. For positive family history of aneurysmal subarachnoid haemorrhage (aSAH) or UIA, the UIA prevalence was 7·9% (5·6–11·1; 412 of 4252 participants) and the adjusted PR was 2·4 (0·5–11·2). For connective-tissue disorder, the UIA prevalence was 10·3% (6·5–16·0; 94 of 879 participants) and the adjusted PR was 3·9 (2·0–7·6). For autosomal dominant polycystic kidney disease (ADPKD), the UIA prevalence was 12·8% (9·2–17·6; 293 of 1990 participants) and the adjusted PR was 4·4 (1·5–12·6). RRs were for current smoking 1·4 (1·2–1·6; 798 of 27911 participants), for having hypertension 1·6 (1·5–1·7, 4043 of 83053 participants), and for female sex 1·9 (1·8–2·0; 3415 of 65020 women and 2122 of 76130 men). In studies on healthy individuals with MR angiography or CT angiography as imaging modality, the prevalence in 2016–2022 was 6·6% (6·3–6·8; 2904 of 41191 participants). The adjusted PR was 1·8 (1·1–2·8) for 2016–2022 versus 2002–2015. Prevalence of UIAs of 5 mm or larger was 0·7% (0·6–0·8) in 2002–2015 and 1·4% (1·0–1·9) in 2016–2022. The UIA prevalence did not differ between countries. τ 2 showed significant heterogeneity between studies. The certainty of the evidence ranged from very low to moderate. Interpretation Prevalence of UIA is increasing, particularly over the past two decades. This increase is only in part explained by improved detection of small UIAs and an ageing population, and other factors—such as environmental—are likely involved. Alongside patients with ADPKD and a positive family history of aSAH, patients with connective-tissue disorders had a higher prevalence of UIA than the reference population. Our findings warrant further investigation into the potential benefit of personalised screening and management strategies in groups at high risk for having UIAs. Funding None.