Computational fluid dynamics analysis of flow reduction induced by flow-diverting stents in intracranial aneurysms: a patient-unspecific hemodynamics change perspective

Abstract

Background and purposeFlow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular aneurysms on the anterior carotid circulation. Intra-aneurysmal flow reduction induces progressive aneurysm thrombosis in most patients. Understanding the degree of flow modification necessary to induce complete aneurysm occlusion among patients with considerable hemodynamics variability may be important for treatment planning.Materials and methodsPatients with incidental intracranial saccular aneurysms who underwent FDS endovascular procedures were included and studied for a 12 months’ follow-up period. We used computational fluid dynamics on patient-specific geometries from 3D rotational angiography without and with virtual stent placement and thus compared intra-aneurysmal hemodynamic problems. Receiver operating characteristic analysis was used to estimate the stent:no-stent minimum hemodynamic ratio thresholds that significantly (p≤0.05) determined the condition necessary for long-term (12 months) aneurysm occlusion.ResultsWe included 12 consecutive patients with sidewall aneurysms located in the internal carotid or vertebral artery. The measured porosity of the 12 deployed virtual FDSs was 83±3% (mean±SD). Nine aneurysms were occluded during the 12 months’ follow-up, whereas three were not. A significant (p=0.05) area under the curve (AUC) was found for spatiotemporal mean velocity reduction in the aneurysms: AUC=0.889±0.113 (mean±SD) corresponding to a minimum velocity reduction threshold of 0.353 for occlusion to occur. The 95% CI of the AUC was 0.66 to 1.00. The sensitivity and specificity of the method were ∼99% and ∼67%, respectively. For both wall shear stress and pressure reductions in aneurysms no thresholds could be determined: AUC=0.63±0.16 (p=0.518) and 0.67±0.165 (p=0.405), respectively.ConclusionsFor successful FDS treatment the post-stent average velocity in sidewall intracranial aneurysms must be reduced by at least one-third from the initial pre-stent conditions.

Is Multiple Overlapping Uncovered Stents Technique Suitable for Aortic Aneurysm Repair?

“…In this study, CFD simulations reveal that the intervention of MOUS markedly reduces flow into the aneurysm sac for both fusiform and saccular aneurysm. In return, TAWSS at the aneurysm wall was reduced significantly as TAWSS reduction is correlated strongly with velocity reduction . Flow characteristics such as low TAWSS, high OSI, and high RRT were quantified at the aneurysm sac especially for fusiform and saccular models deployed with three to four MOUS stents.…”

Virtual-versus-Real Implantation of Flow Diverters: Clinical Potential and Influence of Vascular Geometry

“…Finally, our method also provides crucial information such as the filament location and neck porosity for further hemodynamic evaluation with computational fluid dynamics simulations. [13][14][15][16] …”

“…Furthermore, hemodynamic simulations have shown high potential in predicting intracranial aneurysm thrombosis. [14][15][16] These hemodynamic simulations require reliable and fast virtual stentdeployment methodologies. Therefore, we have recently proposed 17 a virtual stent-deployment method able to predict the local properties of braided stents (wire location, angles, porosities) and implantation parameters (stent length, landing zone) with minimal computational cost.…”

Flow diversion for treatment of intracranial aneurysms: Mechanism and implications

“…31 The aneurysmal flow reduction is determined by the FD's perpendicular flow resistance. Low permeability causes high momentum loss.…”

“…Low permeability causes high momentum loss. 24,31,33 Angiography has been an important imaging tool in assessing aneurysmal hemodynamics and also tracking aneurysmal occlusion at follow-ups posttreatment. Once the force of the FD's perpendicular flow resistance increases to a value higher than the dynamic force, defined as the force driving the blood from the curved parent artery into the aneurysm, blood flow should be mainly restricted from entering the aneurysm and flow along the trajectory of the parent vessel.…”