Objective: The objective of this study was to use parameters to determine the geometric differences between ruptured abdominal aortic aneurysms (AAAs) and nonruptured AAAs. Methods: Computed tomography data of 38 ruptured AAAs and 215 electively repaired (nonruptured) AAAs were collected from multiple institutes. We compared the ruptured AAA group and nonruptured AAA group with 1:1 matching by using the Mahalanobis distance, which was calculated using the patient's age, sex, and AAA diameter. We selected the longitudinal AAA image in multiplanar reconstruction view, placed a hypothetical ellipse on the aneurysm's protruded curve, and placed a circle on the portion connecting the aneurysm and the aorta. We then measured the aspect ratio (the vertical diameter divided by the horizontal diameter) and fillet radius (the radius of arc). Results: The aspect ratio was significantly lower in the ruptured group than in the nonruptured group (2.02 ± 0.53 vs 2.60 ± 1.02; P =.002), as was the fillet radius (0.28 ± 0.18 vs 0.81 ± 0.44; P <.001). Receiver operating characteristic analysis revealed that the area under the curve of the aspect ratio was 0.688, and the optimal cutoff point was 2.23, with sensitivity and specificity of 0.55 and 0.76, respectively. The area under the curve of the fillet radius was 0.933, and the optimal cutoff was 0.347, with sensitivity and specificity of 0.97 and 0.87, respectively. Conclusions: The geometric analysis performed in this study revealed that ruptured AAAs had a smaller fillet radius and smaller aspect ratio than nonruptured AAAs did.
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