Spatial variations in wall thickness, material stiffness and initial shape affect wall stress and shape of intracranial aneurysms

Objective: Saccular aneurysm (sac-like ballooning) is the common form of aneurysm in cerebral arteries. Significant variations exist in the shape, wall thickness and material properties of saccular aneurysms. Aneurysms with irregular shapes are prone to rupture, but the underlying reason is poorly understood. The objective of this study was to examine the effect of spatial variations in wall thickness, material stiffness and initial shape on the shape and wall stress distribution in model aneurysms. Methods: The stress and deformation were determined using non-linear finite element analysis in aneurysm models. Results: Our results showed that local variations in wall thickness and material stiffness led to local stress concentrations and changes to aneurysm shape, and could cause 'bleb' and even a multilobular appearance to the aneurysms. Initial lesion shape also played a significant role in determining the shape of the aneurysms. Discussion: This study demonstrated that spatial variations in wall thickness and material stiffness lead to wall stress concentration in the aneurysm wall and affect the shape of the aneurysms. The stress concentration in the 'bleb' region and in the multilobular aneurysms may explain the observation that irregular shaped and multilobular shaped aneurysms are susceptible to bleeding and rupture.