Association of aneurysm sac-specific eccentricity and abdominal aortic aneurysm rupture risk using computed tomography imaging.

Background: Abdominal aortic aneurysms (AAAs) often exhibit eccentric expansion, making maximum diameter (Dmax) an insufficient indicator of true aneurysm expansion. This study integrates eccentricity into diameter assessment, focusing on the AAA sac to explore its role in predicting AAA rupture risk. Methods: A retrospective case-control study matched ruptured AAA patients with asymptomatic AAA patients based on age and Dmax. Computed tomography imaging data of infrarenal AAAs were analyzed, focusing on the aneurysm body rather than the traditional infrarenal segment. Eccentricity parameters, including Eccentric Diameter and Arch Curvature Ratio, were assessed. Univariate logistic regression evaluated the relationship between morphological variables and AAA rupture, while the area under the receiver operating characteristic (ROC) curve (AUC) analysis compared the performance of different predictive models. Results: Seventy-one ruptured and 71 intact AAA patients were included. Univariate analysis, conducted after diameter matching to exclude the influence of diameter, revealed that the aspect ratio, Eccentric Diameter, and Arch Curvature Ratio of the traditional segment, along with all sac-specific eccentricity parameters, were significantly associated with rupture risk (P<0.05). In subgroups with AAA diameters <55 and <65 mm, sac-specific eccentricity parameters remained significant (P<0.05), whereas traditional segment parameters did not. In model evaluations, sac-specific eccentricity parameters achieved the highest predictive performance. In the overall cohort, the model based on sac-specific Eccentric Diameter and Arch Curvature Ratio yielded an AUC of 0.682 [95% confidence interval (CI): 0.59-0.77; P<0.001], higher than models using Dmax or full-segment parameters. In the <55 and <65 mm subgroups, the model using sac-specific Eccentric Diameter and Arch Curvature Ratio achieved AUCs of 0.692 (P=0.063) and 0.746 (P=0.002), respectively. When combined with Dmax, the corresponding AUCs increased to 0.762 (P=0.011) and 0.776 (P<0.001), representing the highest predictive performance in each subgroup. Conclusions: Focusing on sac-specific eccentricity parameters significantly improves rupture risk prediction, particularly in small-diameter AAA patients, by better capturing the true expansion rate and more sensitively identifying high-risk aneurysms.