Unruptured intracranial aneurysm size should not be the most important factor influencing management decisions: A systematic review of the literature and meta-analysis

Introduction: Intracranial aneurysm size has become an important predictor of rupture risk. There is, perhaps, an overdependence in aneurysm size during evaluations for management decisions. However, many ruptured intracranial aneurysms (RIA) in clinical practice are smaller than 7mm. The purpose of this study is to review the literature and perform a meta-analysis to determine the mean size of RIA in the literature.

Methods: The PubMed, Cochrane, Scopus and Web of Science databases were searched from January 1st, 2000 to October 31st, 2024, following PRISMA guidelines to include clinical studies reporting mean size of RIAs. The pooled mean RIA was calculated. Additional exclusion criteria were applied, and subgroup analyses were performed after dividing the RIAs into a “Lower Risk” group (LRG) and a “Higher Risk” group (HRG) as described in the ISUIA trial.

Results: Between 55 studies, 9876 aneurysms were captured. The pooled mean size for RIAs was 6.57mm (95% CI [6.14-7.00]). Thirty-nine (70.9%) of studies reported mean RIA size < 7mm. Six studies were included in the subgroup analyses, capturing 2774 RIAs. The pooled mean size for RIAs in the subgroup analyses was 5.58mm (95% CI [5.21-5.94]). There were 2076 RIAs in the LRG. The mean RIA size in the LRG was 5.68mm (95% CI [5.26-6.10]). There were 698 RIAs in the HRG. The mean RIA size in the HRG was 5.54mm (95% CI [4.86-6.22]). Spearman’s Rank correlation revealed a very strong positive correlation between RIA size and parent vessel within the LRG (ρ=0.871, ρ < 0.001, 95% CI [0.60–0.96]) and a moderate positive correlation within the HRG (ρ=0.55, p=0.22, 95% CI [0.23–0.97]).

Conclusion : The mean size of RIAs in the literature was 6.57mm. There was a positive correlation between mean RIA size and increasing parent vessel diameter. This supports size ratio (SR) as a more appropriate surrogate for size when assessing rupture risk.