Effect of intraluminal thrombus on wall stress in patient-specific models of abdominal aortic aneurysm

Purpose: The role of intraluminal thrombus (ILT) on abdominal aortic aneurysm rupture is still not clear. Rupture of an aneurysm occurs when the wall stress exceeds the wall strength at any location on the wall. The purpose of this, study was to address the hypothesis that the presence of ILT alters the wall stress distribution or wall stress magnitude in AAA. Methods: Patient-specific 3D AAA geometries were reconstructed from computed tomographic images. Two geometric features, ILT surface ratio (ILT surface area divided by the total AAA surface area) and ILT volume ratio (ILT volume divided by the total AAA volume), were calculated for each AAA. Two models were created for each patient: one with ILT and one without ILT. Systolic pressure measured at the time of computed tomographic imaging was applied to the internal surface of each model. A nonlinear large deformation algorithm was used to compute wall stress distribution with the finite element method. The Wilcoxon matched pairs test was used to compare the peak wall stress between the two models of each patient. Results: Four patients were studied with ILT surface ratios that ranged from 0.29 to 0.72 and ILT volume ratios that ranged from 0.12 to 0.66. The peak wall stress was reduced (range, 6% to 38% reduction; P = .067) for all models with ILT included (range, 28 to 37 N/cm(2)) as compared with models with no ILT (range, 30 to 44 N/cm(2)). Visual inspection also revealed a marked effect of ILT on the wall stress distribution. Conclusion: The presence of ILT alters the wall stress distribution and reduces the peak wall stress in AAA. For this reason, ILT should be included in all patient-specific models of AAA for evaluation of AAA wall stresses.