Deformation and distensibility distribution along the abdominal aorta in the presence of aneurysmal dilatation

Abstract

In order to evaluate the elastic behavior of the abdominal aortic aneurysm (AAA), the distribution of aortic deformation during the cardiac cycle is measured. Moreover, the distensibility of the AAA composite structure consisting of the AAA wall and the intraluminal thrombus (ILT), as well as that of the adjacent non-aneurysmal aortic segment (NAA), are calculated. Ten patients underwent electrocardiographically-gated computed tomography. 3D-surfaces of aortic wall and lumen were reconstructed during peak-systole and end-diastole and cross-sections perpendicular to the centerline were extracted 1 mm apart. Comparison of cross-sectional areas between peak-systole and end-diastole provided the relative area change (RAC). Mean values were calculated for NAA (RACNAA), aneurysmal wall (RACWall), and aneurysmal lumen (RACLumen). Distensibility of aneurysmal and unaffected aorta was calculated using brachial blood pressure measurements (DAAA and DNAA respectively). Normalized distensibility (DNORM) of the AAA was calculated with respect to normal aortic segment distensibility and related to aneurysm size and thrombus content. A map of aortic deformation during the cardiac cycle was obtained. Differences between RACWall (median=0.7%, range=0.3-2.1%) and both RACNAA (median=2.8%, range=0.9-4.8%) and RACLumen (median=1.8%, range=0.5-3.4%) were statistically significant. DAAA (median=0.30∙10-5 Pa-1, range=0.05-0.64∙10-5 Pa-1) was lower than DNAA (median=0.43∙10-5 Pa-1, range=0.16-0.83∙10-5 Pa-1) but difference was not statistically significant. Median DNORM was 0.73 (range=0.1-3.1) and presented a significant positive correlation with AAA size and thrombus content. Aneurysmal wall deforms significantly less than non-aneurysmal wall and aneurysmal lumen, due to altered elastic properties and reduced loading. In large AAAs with larger amounts of ILT, the lumen deformation is comparable or even exceeds that of NAA and subsequently so does the distensibility of the Wall-ILT composite, an observation suggesting a thrombus cushioning effect. DNORM may provide insight in the estimation of AAA evolution and assist in rupture risk assessment.