Background and Purpose The middle cerebral artery (MCA) bifurcation is a preferred site for aneurysm formation. Wider bifurcations 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 3D 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 vessels axes. Statistics were evaluated using Wilcoxon rank-sum analysis and area under the ROC curve (AUC). Results Aneurysmal bifurcations had wider inclination angle γ (median 57.8° vs. 15.4°; p<0.0001). 75% of aneurysmal MCAs had γ>10°, compared to 25% non-aneurysmal. Φ1, Φ2, but especially Φ1+Φ2 were significantly larger in aneurysmal bifurcations (median 171.3° vs. 98.1°; p<0.0001). 67% of aneurysmal bifurcations had Φ1+Φ2>161°, compared to 0% non-aneurysmal MCAs. An optimal threshold of 140° was established for Φ1+Φ2 (AUC=0.98). 68% of aneurysms originating off the daughter branches. 76% 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. Conclusion MCA bifurcations harboring aneurysms have significantly larger branching angles, and more often originate off of the branch with the largest angle. Wider inclination angle is strongly correlated with aneurysm presence, a novel finding. The results point to altered WSS regulation as a possible factor in aneurysm development and progression.
Object. Arterial bifurcations represent preferred locations for aneurysm formation, especially when they are associated with variations in divider geometry. The authors hypothesized a link between basilar apex aneurysms and basilar bifurcation (a) and vertebrobasilar junction (VBJ) angles.Methods. The a and VBJ angles were measured in 3D MR and rotational angiographic volumes using a coplanar 3-point technique. Angle a was compared between age-matched cohorts in 45 patients with basilar artery (BA) aneurysms, 65 patients with aneurysms in other locations (non-BA), and 103 nonaneurysmal controls. Additional analysis was performed in 273 nonaneurysmal controls. Computational fluid dynamics (CFD) simulations were performed on parametric BA models with increasing angles.Results. Angle a was significantly wider in patients with BA aneurysms (146.7° ± 20.5°) than in those with non-BA aneurysms (111.7° ± 18°) and in controls (103° ± 20.6°) (p < 0.0001), whereas no difference was observed for the VBJ angle. A wider angle a correlated with BA aneurysm neck width but not dome size, which is consistent with CFD results showing a widening of the impingement zone at the bifurcation apex. BA bifurcations hosting even small aneurysms (< 5 mm) had a significantly larger a angle compared with matched controls (p < 0.0001). In nonaneurysmal controls, a increased with age (p < 0.0001), with a threshold effect above 35 years of age and a steeper dependence in females (p = 0.002) than males (p = 0.04).Conclusions. The a angle widens with age during adulthood, especially in females. This angular widening is associated with basilar bifurcation aneurysms and may predispose individuals to aneurysm initiation by diffusing the flow impingement zone away from the protective medial band region of the flow divider. (http://thejns.org/doi/abs/10.3171/2014 key WorDS • vessel morphology • basilar bifurcation • vascular disorders • bifurcation aneurysms • vascular age dependencyAbbreviations used in this paper: AUC = area under the curve; BA = basilar artery; CFD = computational fluid dynamics; IA = intracranial aneurysm; MPR = multiplanar reconstruction; MRA = MR angiography; PCA = posterior cerebral artery; ROC = receiver operating characteristic; VBJ = vertebrobasilar junction; WSS = wall shear stress.
The presence of a sidewall aneurysm on the ICA is associated with high curvature in both genders. High curvature of the intracranial ICA, as well as of the distal segment, may indicate a higher risk for aneurysm formation. Non-aneurysmal ICAs are less curved in men than in women, which may explain the gender predisposition to aneurysm formation.
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