Abstract 9937: The Impact of Wall Thickness and Saccular Geometry on the Computational Wall Stress of Descending Thoracic Aortic Aneurysms

Abstract

OBJECTIVES: Wall stress calculated using finite element analysis (FEA) has been used to predict rupture risk of aortic aneurysms. Prior models often assume uniform aortic wall thickness and fusiform geometry. We examined the effects on peak wall stress (PWS) of including local wall thickness, intraluminal thrombus (ILT), and calcifications in FEA of descending thoracic aortic aneurysms. We further investigated the differences in PWS between saccular and fusiform aneurysms. METHODS: CTAs in patients with descending thoracic aortic aneurysms (n=10 total, 5 fusiform and 5 saccular) were analyzed with custom algorithms. For each patient, a control model was defined with uniform wall thickness. Experimental models added the effects of: variable wall thickness (VWT), ILT, and calcifications. A final, combined model incorporated all features. Commercial FEA software was used to load each model with 120 mmHg pressure and compute Von Mises PWS. RESULTS: The mean (n=10) PWS of the control models was 410±111 kPa. The imposition of VWT increased PWS (481±126 kPa, P<0.001) (see Figure). The addition of ILT to VWT (359±86 kPa, p=<0.001) reduced PWS, while the addition of calcifications was not statistically significant (506±126 kPa, P=0.07). The final combined model also reduced PWS (368±88 kPa, P<0.001). Saccular aneurysms had significantly increased stress compared to fusiform aneurysms when normalized by aortic diameter in the control model (104±14 kPa/cm, P=0.04 vs 87±8), but not in the combined model (77±7 kPa/cm vs 67±12, P=0.22). CONCLUSIONS: Incorporation of local wall thickness can significantly increase PWS in FEA models of thoracic aortic aneurysms. Incorporating variable wall thickness, ILT, and calcifications significantly impacts computed PWS of thoracic aneurysms; sophisticated models may therefore be more accurate in assessing rupture risk. Saccular aneurysms did not demonstrate a significantly higher normalized wall stress than fusiform aneurysms.