Background and Purpose:We have demonstrated that stent placement for intracranial aneurysms have a substantial impact on the vascular geometry.In order to analyze subsequent hemodynamics change induced by this geometrical modification,a computational fluid dynamics study was performed.Methods:Four anterior communicating artery and six middle cerebral artery aneurysms,treated with stent-assisted coil embolization,were selected.Two numerical models were created for each aneurysm:1)original vessel and 2)post-treatment vessel whose geometry was altered due to the presence of stent.In both models,the aneurysm sac was first virtually removed and cylindrical characteristics of parent artery branches were restored.The radius of curvature(RC)change on the parent vessel was calculated before and after stent placement.Hemodynamic parameters such as wall shear stress(WSS),pressure and volume flow rate were obtained from the numerical simulation.Results:All treated aneurysms remained stable without recurrence.After stent placement,the RC increased by 9.6 mm on average(from 11.7 ± 4.2 mm to 21.3± 6.5 mm,P＜.001).In region of the "virtual" aneurysm neck,the average WSS after stent placement was significantly lower(reduced to 8.5 ± 2.6 Pa from 12.7 ± 3.0 Pa,P＜.001).Furthermore,there was increased volume flow rate at branch of stent placement(from 4.2 ± 1.3 mL/s to 5.1 ± 0.9 mL/s,P=.176).Conclusion:Stent placement has a substantial effect on the vascular geometry,resulting in reductions of parent vessel curvature and lower hemodynamic stresses,thereby impacting the outcome of treatment.