Hemodynamic Differences Associated With Extreme Versus Minimal Proximal Neck Angulation in Ruptured Infrarenal Abdominal Aortic Aneurysms: A Patient-Specific Computational Study.

BACKGROUND: Maximum aneurysm diameter remains the principal criterion for abdominal aortic aneurysm (AAA) risk assessment, but additional morphologic and biomechanical factors may help explain the heterogeneity of rupture-related vulnerability. This exploratory study aimed to characterize hemodynamic differences associated with extreme versus minimal proximal neck angulation in ruptured infrarenal AAAs. METHODS: Preoperative computed tomography angiography datasets from 6 patients with ruptured infrarenal AAAs were retrospectively analyzed. Cases were categorized into an extreme-angulation group (70° < β < 90°, n = 3) and a minimal-angulation group (β < 5°, n = 3). Patient-specific computational fluid dynamics models were reconstructed to compare intra-sac flow pattern, wall pressure distribution, and wall shear stress (WSS). RESULTS: Compared with minimal angulation, extreme proximal neck angulation was associated with more disturbed intra-sac flow, greater flow acceleration at the neck-sac junction, and more heterogeneous wall pressure and WSS distributions. Minimally angulated aneurysms showed relatively laminar flow, whereas severely angulated aneurysms demonstrated more prominent recirculation and flow disorder. Regions of abnormal hemodynamic behavior showed qualitative spatial concordance with clinically identified rupture sites. CONCLUSION: In this small exploratory series of ruptured infrarenal AAAs, extreme proximal neck angulation was associated with a more adverse intra-sac hemodynamic environment than minimal angulation. These findings are descriptive and hypothesis-generating, do not establish reproducible hemodynamic patterns or rupture-risk prediction, and require validation in larger, preferably multicenter, comparative studies including both ruptured and intact AAAs.