This study investigated the relationship between VBA geometry and BA plaque prevalence. We found that BA plaque prevalence was highest in the Walking geometry (53.06%) and lowest in the Tuning Fork geometry (15.07%). Moreover, the number of vascular bends in the intracranial segments of the VAs and the difference in diameter between the right and left VA also affected the presence of BA plaque.
Yu et al.  have investigated the relationship between the geometry patterns of vertebrobasilar artery and atherosclerosis. In their study, the vertebrobasilar artery geometry was qualitatively classified into four basic configurations: Walking, Tuning, Dominant-Lambda, and Hypoplasia-Lambda. They didn’t focus on the No Confluence Geometry, which plays an important role in the presence of BA plaque. However, in their study, they only explored the correlation between the geometric configurations and BA plaque distribution. In the present study, we investigated the relationship between the geometry of the vertebrobasilar artery system and the presence of BA plaque. In the future study, we also want to determine the relationship between geometric configurations (Walking, Tuning Fork, Lambda, and No Confluence) and the distribution of BA plaque. Besides, in the Yu et al’s study, 84 patients were included in the final analysis. In contrast, our study recruited 290 patients in the final analysis which will increase the power of statistical analysis.
Ravensbergen et al. [18,21,22] in their studies employed autopsy and a series of junction models, and demonstrated that vertebrobasilar geometry affects hemodynamics and that atherosclerotic plaques are often found in regions with complex flow patterns and/or low wall shear stress. In the previous study  high-field MRI was used in conjunction with computational fluid dynamics (CFD) modeling to investigate the hemodynamics of subject-specific confluence models (n = 5, two with Walking, two with Tuning Fork, and one with Dominant-Lambda geometry), and showed that vertebrobasilar geometry strongly influences both the skewing of velocity profiles and wall shear stress distribution in the VBA system. In Walking geometry, the BA flow resulting from the merging of two VAs that bend in the same direction (right) makes the BA flow curve to the opposite direction (left). These chronic processes may induce a BA curvature. The shear stress is low at the inner wall of the BA curvature, and atherosclerotic plaques are prone to form in regions with low shear stress. Also, in the Walking geometry, the BA flow resulting from the VA flows swirling upward makes the flow distribution more complex, which can also induce plaque formation . In the Tuning Fork geometry, the flows in the BA are roughly parallel, and the velocity profile peak in the BA is rather central , resulting in the low BA plaque prevalence in this geometric configuration.
In our study, BA plaque prevalence in the Lambda configuration (27.78%) was higher than that in the Tuning Fork configuration (15.07%). Compared to Lambda patients without BA plaques, those with BA plaques had a larger difference in the diameters of their VAs. In a study by Hong et al.  BA curvature was found to be associated with a diameter difference between the VAs. The BA flow resulting from VAs with a diameter difference ≥ 0.3 mm makes the BA flow curve to the side of the weaker VA, and the chronic processes caused by the asymmetric VA flow induce greater curving of the BA wall, which consequently may cause atherogenesis.
We found that BA plaque prevalence in the No Confluence geometry (37.50%) was also higher than that in the Tuning Fork geometry (15.07%). We hypothesize that BA flow coming from one VA also causes the BA flow curve to the wall opposite to the VA, and as a chronic process may consequently cause a curving of the BA wall. Subsequently, the deformation of the BA wall makes it prone to atherogenesis, which may lead to ischemic stroke in the posterior circulation. To date, there are no hemodynamic studies in patients with No Confluence geometry.
In our study, BA plaque prevalence was higher in patients with multi-bending VAs as compared to patients with oligo-bending VAs. We think that the flow patterns in the first group are more complex than that in the latter.
Our results have important clinical implications. First, we further classified VBA geometry based on the difference in diameter between the VAs and the VA course, which may help to improve the understanding of the vertebrobasilar system. Second, we demonstrated that the Walking, Lambda, and No Confluence geometry, multi-bending of the intracranial VA segment, and a large difference in the diameters of the VAs are high-risk factors for BA atherosclerosis initiation. Therefore, people with these geometric factors should be careful to prevent BA plaque formation.
Our study has several limitations. First, we did not measure the hemodynamics and flow distribution in the four geometric configurations. The underlying mechanism of the basilar artery geometry influencing the development of atherosclerotic plaques needs to be investigated from the hemodynamic aspect in future studies. Second, vascular curvature measurements were done manually from 2D images, since 2D had limited orientation, the vascular curvature at other dimensions cannot be assessed and the processing of vascular curvature measurements may be affected as the effect of flow artifact on 3D-TOF MRA. Third, coronal scanning was performed using the three-dimensional-CUBE sequence, and axial CUBE images were reconstructed. Wall thickness measurements from 3D MPR to determine plaque could be affected by volume averaging artifacts as the image resolution is comparable to the artery wall size, especially, when the basilar artery wall-thickening was not significant. Four, this is a pilot study with a limited sample size. Future studies recruiting larger populations are warranted. Five, even though a cut-off of 0.3 mm was used to define a dominant vertebral artery in previous studies (16,17), the spatial resolution 0.625 × 0.625 × 1.2 mm maybe was not high enough in this study. Finally, this study is an observational cross-sectional design, thus may be influenced by uncontrolled confounding.