Widening and high inclination of the middle cerebral artery bifurcation are associated with presence of aneurysms

Abstract

BACKGROUND AND PURPOSE-: The middle cerebral artery (MCA) bifurcation is a preferred site for aneurysm formation. Wider bifurcation angles have been correlated with increased risk of aneurysm formation. We hypothesized a link between the presence of MCA aneurysms and the angle morphology of the bifurcation. METHODS-: Three-dimensional rotational angiography volumes of 146 MCA bifurcations (62 aneurysmal) were evaluated for angle morphology: parent-daughter angles (larger daughter Φ1, smaller daughter Φ2), bifurcation angle (Φ1+Φ2), and inclination angle (γ) between the parent vessel axis and the plane determined by daughter vessel axes. Statistics were evaluated using Wilcoxon rank-sum analysis and area under the receiver operator characteristic curve. RESULTS-: Aneurysmal bifurcations had wider inclination angle γ (median 57.8° versus 15.4°; P<0.0001). Seventy-five percent of aneurysmal MCAs had γ >10°, compared with 25% nonaneurysmal. Φ1 and Φ2, but especially Φ1+Φ2, were significantly larger in aneurysmal bifurcations (median 171.3° versus 98.1°; P<0.0001). Sixty-seven percent of aneurysmal bifurcations had Φ1+Φ2 >161°, compared with 0% nonaneurysmal MCAs. An optimal threshold of 140° was established for Φ1+Φ2 (area under the curve, 0.98). Sixty-eight percent of aneurysms originated off the daughter branches. Seventy-six percent of them originated off the branch with the largest branching angle, specifically if this was the smaller daughter branch. Wider Φ1+Φ2 correlated with aneurysm neck width, but not dome size. CONCLUSIONS-: MCA bifurcations harboring aneurysms have significantly larger branching angles and more often originate off the branch with the largest angle. Wider inclination angle is strongly correlated with aneurysm presence, a novel finding. The results point to altered wall shear stress regulation as a possible factor in aneurysm development and progression. © 2014 American Heart Association, Inc.