Intraaneurysmal flow and aspect ratio (dome/neck)

It recently has been shown that the aspect ratio (dome/neck) of an aneurysm correlates well with intraaneurysmal blood flow, and the aneurysms of aspect ratio larger than 1.6 carry a higher risk of rupture. We examined the effect of aspect ratio (AR) on intra-aneurysmal flow based on flow visualization studies using various aneurysm models. A flow visualization study with the milk tracing method was performed on ten different aneurysm models, and we calculated the mean transit time (MTT) for each aneurysm model at different flow ratios into the branches. The AR and the MTT for each aneurysm were significantly correlated. It was confirmed that the larger the AR was, the longer the MTT became. An asymetric flow ratio induced smooth circulating flow along the aneurysm wall, but a symmetric flow ratio raised complexed vortices at the neck, resulting in longer MTT for the aneurysm model. Aneurysms growing more than AR 2.0 showed very slow flow, and the bleb at the 2.0 AR aneurysm model showed almost stagnant flow, which is considered a characteristic morphology for rupture. Hemodynamics in the aneurysm larger than AR 2.0 and an accompanying daughter aneurysm at the dome definitely contribute to thrombus formation.