Impact of aneurysm wall enhancement on aneurysm instability: systematic review and meta-analysis of longitudinal studies

Background Aneurysm wall enhancement (AWE) on vessel wall MRI has been proposed as an imaging biomarker of wall inflammation and instability in unruptured intracranial aneurysms (UIAs). However, AWE is frequently observed in aneurysms that remain clinically stable, leaving its prognostic value in longitudinal settings uncertain. We conducted a systematic review and meta-analysis of longitudinal studies to quantify the association between baseline AWE status and subsequent aneurysm instability during follow-up. Methods We searched MEDLINE and Embase for longitudinal studies published between January 1, 2000 and December 13, 2025 that assessed AWE at baseline and reported aneurysm instability during follow-up. Random-effects meta-analyses were performed to estimate pooled risk ratios (RRs), and diagnostic accuracy was evaluated using a bivariate random-effects model. Results Nine studies comprising 2936 UIAs were included. During follow-up, 387 aneurysms (13.2%) demonstrated instability. Newcastle–Ottawa-Scale ranged from 2 to 7, indicating low-to-moderate study quality. Aneurysms with baseline AWE had a higher risk of subsequent instability (pooled RR 2.90; 95% CI 2.2 to 3.81; p<0.001). AWE demonstrated 63% sensitivity and 69% specificity, with a positive likelihood ratio of 2.03 and a negative likelihood ratio of 0.54. Accordingly, AWE positivity increased the post-test probability of instability to 23.5%, whereas AWE negativity reduced it to 7.6%. Conclusions Aneurysms with baseline AWE had an approximately three-fold higher risk of subsequent instability. However, the modest likelihood ratios and limited shifts in post-test probability indicate that AWE should be interpreted cautiously and regarded as an adjunctive marker, rather than a standalone predictor, in individualized UIA risk assessment.