Postoperative Magnetic Resonance Imaging Signal Patterns Predict the Shrinkage of Aneurysms in Large and Giant Intracranial Aneurysms

This study aimed to evaluate whether postoperative T2-weighted magnetic resonance imaging signal patterns can predict aneurysm shrinkage after surgery for large and giant intracranial aneurysms. We retrospectively analyzed 17 patients with large (10-24 mm) or giant (≥25 mm) cerebral aneurysms treated by clipping, trapping, or proximal ligation between 2009 and 2023. Postoperative aneurysmal signal intensity on T2-weighted magnetic resonance imaging was classified as homogeneous or heterogeneous. Aneurysm shrinkage was defined as a ≥50% reduction in maximum diameter at 2 years compared with the preoperative size. Changes in aneurysm diameter and signal patterns were assessed at 6 months, 1 year, and 2 years postoperatively. Statistical analyses included the Mann-Whitney U test for shrinkage rate and Fisher's exact test for categorical variables. In total, 13 aneurysms (76.5%) showed shrinkage, and 4 (23.5%) did not. The homogeneous group demonstrated a significantly greater reduction in aneurysm diameter than the heterogeneous group at 6 months (p = 0.002) and 1 year (p = 0.006), with a similar trend at 2 years (p = 0.051). Some aneurysms initially showing heterogeneous intensity later became homogeneous and subsequently decreased in size. In contrast, persistent heterogeneous signals were associated with poor shrinkage and, in 1 case, regrowth. Postoperative homogeneous signal intensity on T2-weighted magnetic resonance imaging was associated with aneurysm shrinkage, whereas heterogeneous intensity indicated incomplete thrombus organization and limited reduction. Postoperative magnetic resonance imaging signal patterns may serve as a simple imaging biomarker for evaluating thrombus stability and treatment efficacy after surgery for large and giant cerebral aneurysms.