Assessing differences in growth and shape between symptomatic and asymptomatic abdominal aortic aneurysms.

Background: While the risk of abdominal aortic aneurysm (AAA) rupture typically rises with increasing maximum aortic diameter (Dmax), this metric alone does not reflect the full morphological complexity of AAAs and is inadequate for accurately predicting rupture risk. In this study, we aimed to explore differences in growth and shape between asymptomatic AAA (aAAA) and symptomatic AAA (sAAA).

Methods: Patients with infra-renal AAA and ≥2 CTA from 2010-2023 were identified. PRAEVAorta (Nurea, Bordeaux, France) was used to obtain segmentations of the aorta and its branches. Each segmentation was manually reviewed for accuracy using 3D Slicer. Patient demographics, Dmax, AAA flow lumen (AFL), and intraluminal thrombus (ILT) volume were obtained and compared between aAAA and sAAA. A subgroup of aAAA were matched with sAAA on sex and baseline Dmax (12 matched pairs) for comparison of shape, curvature, and 3D-growth. Statistical shape modeling (SSM) derived mean shapes for aAAA and sAAA were compared. Shape [quantified using distance to centerline (DC) in cm], curvature, and 3D-growth (defined as the difference in shape over time) were compared over eight aortic segments.

Results: Fifty-five patients with AAA (12 sAAA) were included (47.3% female). Patients with sAAA were younger than those with aAAA [66.0 (60.9, 70.1) vs. 71.0 (65.3, 74.9) years, P=0.026], less likely to be Caucasian (75.0% vs. 95.3%, P=0.030), and less likely to have hypertension (50.0% vs. 81.4%, P=0.027). There was no difference in AAA Dmax (4.6 vs. 4.8 cm), volume (103.5 vs. 98.7 mm³), AFL (65.4 vs. 52.8 mm³), or ILT volume (37.9 vs. 36.7 mm³) between aAAA and sAAA. Although there was no difference in change of Dmax over time, sAAA had larger increases in AAA volume [1.6 (1.1, 7.8) vs. 1.1 (0.4, 2.1) cm³/month, P=0.019] and AFL volume [1.1 (0.5, 5.7) vs. 0.4 (0.2, 1.2) cm³/month, P=0.017] than aAAA. Despite possible qualitative shape differences seen on SSM, quantifiable differences in shape or curvature between aAAA and sAAA were not identified across eight aortic segments. At the left lateral aneurysm neck, sAAA had higher 3D-growth than aAAA [0.17 (0.05, 0.55) vs. 0.01 (-0.03, 0.14) mm/month, P=0.027].

Conclusions: sAAA had larger increase in AAA volume and AFL volume over time when compared to aAAA (despite no difference in diameter, volume, or change in diameter). Despite no quantifiable differences in shape or curvature between aAAA and sAAA, sAAA had larger 3D-growth in the left lateral aneurysm neck compared to aAAA. Volumetric changes, shape, and 3D-growth may be better predictors of AAA rupture risk. However, larger scale studies are warranted to confirm these preliminary findings and explore the mechanisms underlying these differences.