Stent-assisted coil embolization (SACE) is widely accepted for the endovascular treatment of wide-neck or complex cerebral aneurysms. Dr. Kenichi Kono and his team at the Showa University Fujigaoka Hospital of Kanagawa in Japan have assessed and compared the hemodynamic effect of stent struts and straightening of vessels. They tested out the effects of stent placement on reducing flow velocity in sidewall cerebral aneurysms with the goal of reducing recanalization rates. Thanks to this groundbreaking study, Dr. Kono was the Global Mimics Innovation Award winner in 2015.
(A) An angiogram shows a sidewall aneurysm in the left vertebral artery. (B) Six months after a stent-assisted coil embolization for the aneurysm, an angiogram shows the complete occlusion of the aneurysm and straightening of the vessel. (C) The two 3D images of the vessel and the aneurysm at pre- (in red) and post-treatment (in blue) are fused. (D) The ‘‘inflow angle’’ and ‘‘outflow angle’’ are defined as angles between the neck plane of an aneurysm and an inflow line or an outflow line. The angles can be negative when the angles show opposite directions.
First study on the hemodynamic effects of stent struts and the straightening of vessels
Recent clinical studies have shown that recanalization rates are lower in stent-assisted coil embolization as opposed to non-assisted coiling in the treatment of cerebral aneurysms. This situation probably occurs because of two types of hemodynamic effects produced by stent placement: stent struts and the straightening of vessels.
According to the researchers, the hemodynamic effects of stent struts have been widely studied with computational fluid dynamics (CFD) simulations and in vitro experiments. Hemodynamic studies on the straightening of vessels have also been reported. However, this is the first report to compare the hemodynamic effects caused by stent struts and those of the straightening of vessels in SACE.
CFD simulations of sidewall cerebral aneurysms
Dr. Kono and his team performed CFD simulations of 16 patient-specific sidewall aneurysms treated with SACE. The simulations were performed before and after treatment, with and without stent struts.
The researchers first obtained 3D images of the vascular geometry of the patients with a 3D rotational angiography, before and 6 months after the stent placement. The two images were fused using Materialise 3-matic, by choosing three points located at similar regions on both 3D images. Next, Dr. Kono and his team performed a manual registration based on the geometry of the aneurysm and a parent vessel near the aneurysm.
While performing the CFD simulations, they were able to determine the main factor that was reducing the flow velocity in aneurysms and recanalization rates.
They concluded that in sidewall aneurysms, stent struts have stronger effects (approximately two times more) on the reduction in flow velocity, as opposed to the straightening of vessels. Hemodynamic effects with straightening vary in each case and can be predicted by the inflow of angles of the pre-operative vessel geometry. These results may be useful to design a treatment strategy for reducing recanalization rates.
Contours of the cut plane are colored according to mean flow velocity. The white arrow in the pre-treatment image indicates the flow direction. Flow velocity was reduced by 20% after placement of stent struts on the initial geometry. Flow velocity was reduced by 211% (i.e., increased by 11%) after straightening of a vessel without stent struts. The combination of both stent struts and straightening resulted in a flow reduction of 15%. Straightening of the vessel changed the inflow angle from -24° to -15°.
About the author
Dr. Kenichi Kono is a neurosurgeon and an assistant professor at the Department of Neurosurgery, Showa University Fujigaoka Hospital of Kanagawa in Japan. He is specialized in endovascular treatments and open-skull surgery. He is a user of Materialise 3-matic and performs computational fluid dynamic simulations. In 2015, Dr. Kono received the Global Mimics Innovation Award with his research on hemodynamic effects of stent struts versus straightening of vessels in stent-assisted coil embolization for sidewall cerebral aneurysms.
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