Malek Adel M, Hippelheuser James E, Lauric Alexandra
1Department of Neurosurgery, Tufts Medical Center and Tufts University School of Medicine, Boston, Massachusetts.
J Neurosurg. 2021 Oct 29;136(6):1726-1737. doi: 10.3171/2021.6.JNS204385. Print 2022 Jun 1.
Aneurysm formation preferentially occurs at the site of wide-angle cerebral arterial bifurcations, which were recently shown to have a high longitudinal positive wall shear stress (WSS) gradient that promotes aneurysm formation. The authors sought to explore the other components of the hemodynamic environment that are altered with increasing bifurcation angle in the apical region and the effects of these components on WSS patterns on the vessel wall that may modulate aneurysm genesis and progression.
Parametric models of symmetrical and asymmetrical bifurcations were created with increasing bifurcation angles (45°-240°), and 3D rotational angiography models of 13 middle cerebral artery (MCA) bifurcations (7 aneurysmal, 6 controls) were analyzed using computational fluid dynamics. For aneurysmal bifurcations, the aneurysm was digitally removed to uncover hemodynamics at the apex. WSS vectors along cross-sectional planes distal to the bifurcation apex were decomposed as orthogonal projections to the cut plane into longitudinal and transverse (tangential to the cross-sectional plane) components. Transverse rotational WSS (TRWSS) and TRWSS gradients (TRWSSGs) were sampled and evaluated at the apex and immediately distal from the apex.
In parametric models, increased bifurcation angle was associated with transverse flow vortex formation with emergence of an associated apical high TRWSS with highly aneurysmogenic positive TRWSSGs. While TRWSS decayed rapidly away from the apex in narrow-angle bifurcations, it remained greatly elevated for many radii downstream in aneurysm-prone wider bifurcations. In asymmetrical bifurcations, TRWSS was higher on the aneurysm-prone daughter vessel associated with the wider angle. Patient-derived models with aneurysmal bifurcations had wider angles (149.33° ± 12.56° vs 98.17° ± 8.67°, p < 0.001), with significantly higher maximum TRWSS (1.37 ± 0.67 vs 0.48 ± 0.23 Pa, p = 0.01) and TRWSSG (1.78 ± 0.92 vs 0.76 ± 0.50 Pa/mm, p = 0.03) compared to control nonaneurysmal bifurcations.
Wider vascular bifurcations are associated with a novel and to the authors' knowledge previously undescribed transverse component rotational wall shear stress associated with a positive (aneurysmogenic) spatial gradient. The resulting hemodynamic insult, demonstrated in both parametric models and patient-based anatomy, is noted to decay rapidly away from the protection of the medial pad in healthy narrow-angle bifurcations but remain elevated distally downstream of wide-angle aneurysm-prone bifurcations. This TRWSS serves as a new contribution to the hemodynamic environment favoring aneurysm formation and progression at wide cerebral bifurcations and may have clinical implications favoring interventions that reduce bifurcation angle.
动脉瘤形成优先发生在大脑动脉宽角分叉处，最近研究表明此处具有较高的纵向正向壁面切应力（WSS）梯度，可促进动脉瘤形成。作者试图探究顶端区域随分叉角度增加而改变的血流动力学环境的其他组成部分，以及这些组成部分对血管壁上WSS模式的影响，这些影响可能调节动脉瘤的发生和发展。
创建了具有不同分叉角度（45° - 240°）的对称和不对称分叉的参数模型，并使用计算流体动力学分析了13个大脑中动脉（MCA）分叉（7个动脉瘤性，6个对照）的三维旋转血管造影模型。对于动脉瘤性分叉，通过数字方式去除动脉瘤以揭示顶端的血流动力学。沿着分叉顶端远端的横截面的WSS向量被分解为与切割平面正交的投影，分为纵向和横向（与横截面切线方向）分量。在顶端和紧挨着顶端远端处采样并评估横向旋转WSS（TRWSS）和TRWSS梯度（TRWSSG）。
在参数模型中，分叉角度增加与横向流涡旋形成相关，伴随着顶端高TRWSS的出现以及具有高度致动脉瘤性的正向TRWSSG。在窄角分叉中，TRWSS从顶端迅速衰减，而在易发生动脉瘤的宽角分叉中，在许多半径下游它仍保持在较高水平。在不对称分叉中，与较大角度相关的易发生动脉瘤的子血管上的TRWSS更高。患有动脉瘤性分叉的患者来源模型具有更宽的角度（149.33°±12.56°对98.17°±8.67°，p < 0.001），与对照非动脉瘤性分叉相比，最大TRWSS（1.37±0.67对0.48±0.23 Pa，p = 0.01）和TRWSSG（1.78±0.92对0.76±0.50 Pa/mm, p = 0.03）显著更高。
更宽的血管分叉与一种新的、据作者所知以前未描述的横向分量旋转壁面切应力相关，该切应力具有正向（致动脉瘤性）空间梯度。在参数模型和基于患者的解剖结构中均显示，由此产生的血流动力学损伤在健康的窄角分叉中远离内侧垫的保护时迅速衰减，但在易发生动脉瘤的宽角分叉下游远端仍保持升高。这种TRWSS是对有利于大脑宽角分叉处动脉瘤形成和发展的血流动力学环境的新贡献，可能对有利于减小分叉角度的干预措施具有临床意义。
