Hemodynamic effects of stent struts versus straightening of vessels in stent-assisted coil embolization for sidewall cerebral aneurysms

Abstract

Background: Recent clinical studies have shown that recanalization rates are lower in stent-assisted coil embolization than in coiling alone in the treatment of cerebral aneurysms.

Objective: This study aimed to assess and compare the hemodynamic effect of stent struts and straightening of vessels by stent placement on reducing flow velocity in sidewall aneurysms, with the goal of reducing recanalization rates.

Methods: We evaluated 16 sidewall aneurysms treated with Enterprise stents. We performed computational fluid dynamics simulations using patient-specific geometries before and after treatment, with or without stent struts.

Results: Stent placement straightened vessels by a mean (±standard deviation) of 12.9° ± 13.1° 6 months after treatment. Placement of stent struts in the initial vessel geometries reduced flow velocity in aneurysms by 23.1% ± 6.3%. Straightening of vessels without stent struts reduced flow velocity by 9.6% ± 12.6%. Stent struts had significantly stronger effects on reducing flow velocity than straightening (P = 0.004, Wilcoxon test). Deviation of the effects was larger by straightening than by stent struts (P = 0.01, F-test). The combination of stent struts and straightening reduced flow velocity by 32.6% ± 12.2%. There was a trend that larger inflow angles produced a larger reduction in flow velocity by straightening of vessels (P = 0.16).

Conclusion: In sidewall aneurysms, stent struts have stronger effects (approximately 2 times) on reduction in flow velocity than straightening of vessels. Hemodynamic effects by straightening vary in each case and can be predicted by inflow angles of pre-operative vessel geometry. These results may be useful to design a treatment strategy for reducing recanalization rates.

Figure 1. Angiograms and illustrations of straightening of vessels by stent placement in Case 1.

(A) An angiogram shows a sidewall aneurysm at the left vertebral artery. (B) Six months after stent-assisted coil embolization for the aneurysm, an angiogram shows complete occlusion of the aneurysm and straightening of the vessel. (C) 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, respectively. The angles can be negative when the angles show opposite directions.

Figure 2. Illustrations of hemodynamic analysis of reduction in flow velocity in an aneurysm of Case 1.

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 −11% (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°.

Figure 3. Reduction in flow velocity in 16 cases by either stent struts or straightening of vessels.

Figure 4. Correlations among pre-operative inflow angle, changes in inflow angle, and flow reduction by vessel straightening.