Numerical study of hemodynamic changes in the Circle of Willis after stenosis of the internal carotid artery

In clinical practice a large number of patients with ischemic stroke have internal carotid artery (ICA) stenosis accompanied by Circle of Willis (CoW) stenosis. In the presence of carotid artery stenosis, CoW atherosclerosis may cause cerebral blood flow decompensation and may promote the development of ischemic stroke. The reason for the concomitant stenosis at both sites is unknown. This study investigated the hemodynamic effects of ICA stenosis on the CoW.We developed a three-dimensional/zero-dimensional (3D/0D) closed-loop geometric multiscale model of the cerebral artery to quantify the hemodynamic indicators, including time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI). Mild (<50 %), moderate (50-69 %) and severe (>69 %) ICA stenoses were established based on 3D models of cerebral arteries in two volunteers. Geometric multiscale computing models were numerically evaluated to obtain local hemodynamic changes in the CoW in order to assess the risk of stenosis in the CoW.Model calculations showed that for all 3D models the A1 segment of the anterior cerebral artery (ACA) or the posterior communicating artery (PCA) within the CoW exhibited a hemodynamic environment with high OSI (>0.2) and low TAWSS (<1 Pa) when the ICA had a moderate stenosis. While in the case of mild and severe stenosis in ICA, there is no such phenomenon. The proportion of the surface area possessing high OSI and low TAWSS in the A1 segment of the ACA or in the PCA was mostly greater than 60 %, which might potentially cause the formation and development of atherosclerosis in CoW and finally lead to CoW stenosis.Therefore, although moderate carotid artery stenosis may not cause ischemic stroke, it may cause hemodynamic changes in the CoW, which in turn may promote CoW stenosis and cause CoW decompensation. In clinical treatment attention should be paid not only to stenosis of the carotid arteries but also to changes in the hemodynamic environment within the CoW, in order to prevent the adverse effects of CoW stenosis.