Association between Pre-operative Aneurysm Diameter and One Year Sac Behaviour following Endovascular Aneurysm Repair

This retrospective cohort study assessed the association between aneurysm diameter and one year sac behaviour.

All endovascular aortic repairs (EVARs) with one year imaging follow up in the Vascular Quality Initiative (2003 - 2024) were included. Sac behaviour was defined as expansion (≥ 5 mm enlargement), regression (≥ 5 mm shrinkage), or stable (< 5 mm change). Aneurysm diameter was categorised by sex specific thresholds (women/men): < 45/< 50 mm, 45 - 50/50 - 55 mm, 50 - 55/55 - 60 mm, 55 - 60/60 - 65 mm, 60 - 65/65 - 70 mm, and > 65/> 70 mm. Sac behaviour was estimated using multinomial logistic regression, with sac stability and 50 - 55/55 - 60 mm as reference categories. Restricted cubic splines (RCS) were incorporated to explore the continuous relationship.

A total of 28 275 patients were included. At one year, 48.5% had sac regression, 45.4% stability, and 6.1% expansion. Using 50 - 55/55 - 60 mm as the diameter reference and sac stability as the outcome reference, adjusted odds ratios (95% confidence interval) for sac regression were 0.40 (0.37 - 0.43) for < 45/< 50 mm, 0.82 (0.77 - 0.86) for 45 - 50/50 - 55 mm, 1.25 (1.17 - 1.33) for 55 - 60/60 - 65 mm, 1.38 (1.29 - 1.48) for 60 - 65/65 - 70 mm, and 1.46 (1.37 - 1.57) for > 65/> 70 mm. Corresponding odds ratios for expansion were 1.92 (1.88 - 1.95), 1.03 (1.02 - 1.04), 1.20 (1.18 - 1.21), 1.43 (1.41 - 1.45), and 1.67 (1.64 - 1.69), respectively. RCS demonstrated that regression increased steeply with diameter up to ∼55 mm, while stability declined progressively. Expansion was most common in small aneurysms and least likely near 55 mm.

Pre-operative aneurysm diameter showed a non-linear association with one year sac behaviour. Sac regression increased up to ∼55 mm, where the predicted probability of expansion was lowest. Small aneurysms had nearly twofold higher odds of expansion relative to stability. In larger aneurysms, higher odds of expansion reflected lower stability rather than a meaningful rise in absolute expansion risk. Further investigation is needed to clarify the mechanisms underlying sac expansion in small aneurysms. These findings suggest that patients treated at small diameters may require closer surveillance.