Aim: The aim of this study was to examine the effect of intraluminal thrombus (ILT) on the peak wall stress (PWS) in abdominal aorta aneurysm models (AAA).
Methods: Anatomically correct patient specific AAA models were created by 3D reconstruction of in vivo acquired computed tomography images from 19 male patients. Patients were divided in two groups according to aneurysm peak transverse diameter, 5-7 cm (10 patients, ''intermediate'' group) and >7 cm (9 patients, ''large'' group), respectively. PWS was evaluated in the presence and absence of ILT. The percentage of PWS reduction (Delta PWS %) was estimated as a percentage of PWS value in the absence of ILT. Finite element analysis was used to numerically compute the wall stress distribution assuming a 2-mm thick hyperelastic AAA wall material model and a 120 mmHg systolic uniform wall loading. The thrombus was modeled as an isotropic, elastic, homogenous and incompressible material. The volume of ILT was estimated as a percentage of the AAA sac volume.
Results: The ILT volume was 49.9%+/-10.6% in the ''large'' group and 58.6%+/-13.2% in the ''intermediate'' group (t-test P=0.14). The ''large'' AAAs have higher PWS values than the ''intermediate'' group, both in the presence of ILT (36.9+/-5.8 vs. 23.5+/-6.2 Nt/cm(2), P=0.0001) as well as in the absence of ILT (52.6+/-15.4 vs. 35.0+/-10.5 Nt/cm(2), P=0.01). The presence of ILT resulted in a decrease of PWS (Delta PWS) in all cases. There was no statistical difference between the two groups in the mean PWS reduction, in the presence of ILT (26.9+/-12.5 Nt/cm(2) in the ''large'' group and 31.0+/-11.7 Nt/cm2 in the ''intermediate'' group, t-test P=0.48). However, a strong correlation between the ILT relative volume (ILT%) and the degree of PWS reduction was found only in the ''intermediate'' AAA group (Pearson correlation 0.86, P<0.001), whereas no correlation was observed in the ''large'' AAA group (Pearson correlation 0.05, P=0.9).
Conclusions: The presence of ILT reduced the PWS in all cases. In the ''intermediate'' AAAs our results showed a linear correlation between ILT relative volume and cents PWS. However, in ''large'' aneurysms no such correlation was found. This indicates that the degree of ILT influence on the reduction of PWS in ''large'' AAAs may be related to other factors such as the geometric configurations of the AAA.