Multiaxial mechanical behavior of human saccular aneurysms

Intracranial saccular aneurysms are focal dilatations of the arterial wall that usually occur in or near the circle of Willis. Two-to-five percent of the population in the western world likely harbors such an aneurysm, rupture of which is the leading cause of nontraumatic subarachnoid hemorrhage. It is widely thought that these lesions rupture when wall stress exceeds wall strength. Given that aneurysms experience multiaxial stress and strain fields in vivo, there is a pressing need for data on their multiaxial mechanical properties. In this paper, we report the first multiaxial data on human saccular aneurysms. Lesions were obtained at autopsy, cannulated, and subjected to cyclic pressurization using a triplane video-based experimental system. The latter recorded the pressures and associated motions of multiple markers that were affixed to the surface of the lesion. Finally, a new sub-domain inverse finite element method was used to estimate the best-fit material parameters in a Fung-type pseudostrain energy function. It was found that the lesions were much stiffer than previously thought, which in turn will affect significantly any estimation of wall stress. There remains a need, however, to collect data on additional specimens, to evaluate different descriptors of the multiaxial behavior, and to correlate these findings with direct measures of the underlying histology.