Widening of the basilar bifurcation angle: association with presence of intracranial aneurysm, age, and female sex

Abstract

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.

Morphological and Hemodynamic Risk Factors for Middle Cerebral Artery Aneurysm: a Case-Control Study of 190 Patients

“…Importantly, non-aneurysmal MCA bifurcations analyzed in our present study had significantly higher values of α angle than the control bifurcations. These results correspond to those reported by other authors, according to whom patients with aneurysms presented with significantly wider non-aneurysmal bifurcation angles than the healthy controls 14,38 . This implies that persons with aneurysms might also show significant alterations in vascular dimensions and bifurcation angles of other arteries, and thus, might be predisposed to formation of de novo or multiple aneurysms.…”

“…3D rotational angiography, MRA, CTA) dealing with the problem of bifurcation angle morphology showed that wide bifurcation angle constitutes a significant risk factor for aneurysm formation. Those studies included the bifurcations which are generally considered to be predisposed for aneurysm development: ACoA complex 8,16,[34][35][36] , BA 14,29,37 and MCA 30,38 . Our findings are consistent with the results of the studies mentioned above; our present study showed that Φ 1 , Φ 2 and α angles in aneurysmal MCA bifurcations were significantly wider than in contralateral and control bifurcations.…”

“…However, it is still unclear which factors determine the magnitude of the hemodynamic stress at arterial bifurcation. The results of studies with glass vessel models 3,11,12 and computational fluid dynamics (CFD) studies [13][14][15][16] suggest that the magnitude of the hemodynamic stress and its distribution at arterial bifurcation might depend on the blood flow characteristics, as well as on the bifurcation's geometry, i.e. bifurcation angle and vascular dimensions.…”

Induction of aneurysmogenic high positive wall shear stress gradient by wide angle at cerebral bifurcations, independent of flow rate

“…17 Aneurysm presence at cerebral bifurcations was recently shown to be associated with wider bifurcation angles in both middle cerebral and basilar bifurcations. 1,21,25 Basilar bifurcations may widen with age, more so in women, possibly triggering tissue degeneration due to changes in the local hemodynamic environment. 25 Although the mechanism for aneurysm initiation is not completely understood, consensus is building regarding the disruptive role of local high WSS and high positive WSSG in the pathological process of aneurysm origination.…”

“…1,21,25 Basilar bifurcations may widen with age, more so in women, possibly triggering tissue degeneration due to changes in the local hemodynamic environment. 25 Although the mechanism for aneurysm initiation is not completely understood, consensus is building regarding the disruptive role of local high WSS and high positive WSSG in the pathological process of aneurysm origination. 5,6,17,24 Studies in animals subjected to unilateral or bilateral common carotid artery ligation have shown that, without other known predisposing factors, flow increase alone at cerebral bifurcations can lead to EC remodeling consistent with aneurysm initiation.…”