Patient- and Aneurysm-Specific Risk Factors for Intracranial Aneurysm Growth: A Systematic Review and Meta-Analysis

BACKGROUND AND PURPOSE—: Follow-up imaging is often performed in intracranial aneurysms that are not treated. We performed a systematic review and meta-analysis on patient- and aneurysm-specific risk factors for aneurysm growth. METHODS—: We searched EMBASE and MEDLINE for cohort studies describing risk factors for aneurysm growth. Two authors independently assessed study eligibility and rated quality with the Newcastle Ottawa Scale. With univariable Poisson regression analysis, we calculated risk ratios (RRs) with corresponding 95% confidence intervals (95% CI) of risk factors for aneurysm growth. Heterogeneity was assessed with I. RESULTS—: Eighteen studies on 15 patient-populations described 3990 patients with 4972 unruptured aneurysms. A total of 437 aneurysms (9%) enlarged during 13 987 aneurysm-years of follow-up. Compared with aneurysms ≤4 mm, RRs were 2.56 (95% CI, 1.93–3.39; I=98%) for ≥5 mm, 2.80 (95% CI, 2.01–3.90; I=96%) for ≥7 mm, and 5.38 (95% CI, 3.76–7.70; I=97%) for ≥10 mm. Compared with aneurysms on the middle cerebral artery, the RR for basilar artery was 1.94 (95% CI, 1.32–2.83; I=57%). RRs were 2.03 (95% CI, 1.52–2.71; I=59%) for smoking at baseline, 2.04 (95% CI, 1.56–2.66; I=90%) for multiple unruptured aneurysms, 1.26 (95% CI, 0.97–1.62; I=59%) for women, 1.24 (95% CI, 0.98–1.58; I=40%) for hypertension, and 2.32 (95% CI, 1.46–3.68; I=91%) for irregular aneurysm shape. Compared with other regions, RR was 0.75 (95% CI, 0.58–0.96) for Japan and 0.64 (95% CI, 0.45–0.90) for Finland. CONCLUSIONS—: Most risk factors for aneurysm growth are consistent with risk factors for rupture. In contrast with rupture, the risk of growth was smaller in Japanese and Finnish cohorts compared with other regions. Pooling of individual patient data from low- and high-risk geographical regions is needed to assess independent predictors of aneurysm growth.