Volume growth of abdominal aortic aneurysms correlates with baseline volume and increasing finite element analysis-derived rupture risk

Background: The diagnosis and management of abdominal aortic aneurysms (AAAs) currently relies on the aortic maximal diameter, which grows in an unpredictable manner. Infrarenal aortic volume has recently become clinically feasible to measure, and an estimate of biomechanical rupture risk derived from finite element analysis, the peak wall rupture index (PWRI), has been shown to predict AAA rupture. Our objective was to ascertain how well volume growth correlates with baseline volume and increasing PWRI, compared with the maximal diameter. Methods: We retrospectively identified 41 AAA patients (nine women, 32 men) at our institution who had undergone two computed tomography angiographies with an interval of 8 to 17 months. Digital three-dimensional reproductions of the aneurysms were segmented from the 82 computed tomography angiographies. AAA diameter, volume, and PWRI were measured and calculated with finite element analysis software. Growth rates of diameter and volume were related to baseline diameter and volume as well as to change rates of PWRI. Significant growth was defined as growth exceeding our interobserver 95% limits of agreement. Results: Diameter growth rate did not correlate with baseline diameter (r = 0.15, 95% confidence interval [CI], -0.17 to 0.45), but volume growth rate correlated with baseline volume (r = 0.56; 95% CI, 0.30-0.75). The correlation between baseline volume and volume growth rate was stronger than the correlation between baseline diameter and diameter growth rate (95% CI, 0.086-0.71). Increasing PWRI correlated with volume growth rate (r = 0.70; 95% CI, 0.40-0.87) but not with diameter growth rate (r = 0.044; 95% CI, -0.44 to 0.51), and the difference between the correlation coefficients was significant (95% CI, 0.11-1.16). Conclusions: Volume better predicts aneurysm growth rate and correlates stronger with increasing estimated biomechanical rupture risk compared with diameter. Our results support the notion of monitoring all three dimensions of an AAA.