Wall stress distribution on three-dimensionally reconstructed models of human abdominal aortic aneurysm

Purpose: Abdominal aortic aneurysm (AAA) rupture is believed to occur when the mechanical stress acting on the wall exceeds the strength of the wall t issue. Therefore, knowledge of the stress distribution in an intact AAA wal l could be useful in assessing its risk of rupture. We developed a methodol ogy to noninvasively estimate the in vivo wall stress distribution for actu al AAAs on a patient-to-patient basis. Methods: Six patients with AAAs and one control patient with a nonaneurysma l aorta were the study subjects. Data from spiral computed tomography scans were used as a means of three-dimensionally reconstructing the in situ geo metry of the intact AAAs and the control aorta. We used a nonlinear biomech anical model developed specifically for AAA wall tissue. By means of the fi nite element method, the stress distribution on the aortic wall of all subj ects under systolic blood pressure was determined and studied. Results: In all the AAA cases, the wall stress was complexly distributed, w ith distinct regions of high and low stress. Peak wall stress among AAA. pa tients varied from 29 N/cm(2) to 45 N/cm(2) and was found on the posterior surface in all cases studied. The wall stress on the nonaneurysmal aorta in the control subject was relatively low and uniformly distributed, with a p eak wall stress of 12 N/cm(2). AAA volume, rather than AAA diameter, was sh own by means of statistical analysis to be a better indicator of high wall stresses and possibly rupture. Conclusion: The approach taken to estimate AAA wall stress distribution is completely noninvasive and does not require any additional involvement or e xpense by the AAA patient. We believe that this methodology may allow for t he evaluation of an individual AAA's rupture risk on a more biophysically s ound basis than the widely used 5-cm AAA diameter criterion.