A Hemodynamic Mechanism Correlating with the Initiation of MCA Bifurcation Aneurysms

Abstract

BACKGROUND AND PURPOSE: Previous studies have reported that MCA bifurcation aneurysms usually emerge on inclined bifurcations; however, the reason is unclear. We designed this study to explore hemodynamic mechanisms that correlate with the initiation of MCA bifurcation aneurysms. MATERIALS AND METHODS: Fifty-four patients with unilateral MCA bifurcation aneurysms and 54 control patients were enrolled in this study after propensity score matching, and their clinical and CTA data were collected. We extracted the morphologic features of aneurysmal MCA bifurcations to build a simplified MCA bifurcation model and performed a computational fluid dynamics analysis. RESULTS: The presence of MCA aneurysms correlated with smaller parent-daughter angles of MCA bifurcations (P , .001). Aneurysmal MCA bifurcations usually presented with inclined shapes. The computational fluid dynamics analysis demonstrated that when arterial bifurcations became inclined, the high-pressure regions and low wall shear stress regions shifted from the apexes of the arterial bifurcations to the inclined daughter arteries, while the initial sites of MCA bifurcation aneurysms often overlapped with the shifted high-pressure regions and low wall shear stress regions. CONCLUSIONS: Our results suggest that the initiation of MCA bifurcation aneurysms may correlate with shifts of high-pressure regions and low wall shear stress regions that occur on inclined MCA bifurcations. ABBREVIATIONS: CFD ¼ computational fluid dynamics; HPR ¼ high-pressure region; LWSS ¼ low wall shear stress; LWSSR ¼ low wall shear stress region; PSM ¼ propensity score matching; RD ¼ ratio of diameter; ROC ¼ receiver operating characteristic T he occurrence of intracranial aneurysms is generally thought to be due to arterial wall weakening and/or the influence of hemodynamics. 1-4 Most studies on aneurysm etiology have focused on hemodynamics. Because the geometric shapes of intracranial arteries are diverse, their hemodynamics are also complex. Arterial bifurcations are common sites for intracranial aneurysms. The bifurcations are generally exposed to extreme hemodynamic stress; those with special morphologic features that significantly divert blood flow from the direction of flow of the parent vessels are a risk factor for aneurysm formation. 1,5,6 Previous studies have reported that the inclined MCA bifurcations with a widening angle are likely to harbor aneurysms, 7,8 but mechanisms by which the aneurysms develop on MCA bifurcations are controversial and need to be elucidated. 8-11 The present study was designed to extract the morphologic features of aneurysmal MCA bifurcations from clinical data, build a simplified MCA bifurcation model based on these extracted features, perform computational fluid dynamics (CFD) analysis on the aneurysmal MCA bifurcations and simplified models, and finally, to explore the hemodynamic mechanisms that could trigger aneurysm initiation. MATERIALS AND METHODS Case Selection and Matching Patients with unilateral MCA bifurcation aneurysms confirmed ...

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