Hypoplastic Vertebral Artery Contributes to Stroke by Promoting Progression of Basilar Artery Bending

BACKGROUND: As a well-recognized vascular variation, hypoplastic vertebral artery has been recognized as a potential risk for stroke. We aimed to assess the odds of new-onset stroke over a 20-year period in subjects with versus without hypoplastic vertebral artery, exploring how the progression of basilar artery bending mediates the odds. METHODS: This was a retrospective cohort study, with 20 years of follow-up (2004-2024, analysis performed in June 2025). The primary outcome was the occurrence of new-onset posterior circulation infarction during follow-up. Logistic regression models were fitted for new-onset posterior circulation infarction as gender, baseline stroke, baseline posterior circulation infarction, basilar artery stenosis during follow-up, the progression of basilar artery bending, and hypoplastic vertebral artery. Mediation analyses were conducted for vertebral artery stenosis during follow-up, basilar artery stenosis during follow-up, and the progression of basilar artery bending. RESULTS: A total of 1464 subjects were included, 547 with hypoplastic vertebral artery. During the 20-year follow-up, 91 participants had new-onset posterior circulation infarction. The occurrence of new-onset posterior circulation infarction was significantly associated with progression of basilar artery bending (odds ratio 1.700, 95% confidence interval 1.032-2.798, p = 0.037) and hypoplastic vertebral artery (odds ratio 1.481, 95% confidence interval 1.019-2.003, p = 0.015). The proportion of new-onset posterior circulation infarction attributable to hypoplastic vertebral artery was mediated by the progression of basilar artery bending, accounting for approximately 50.2% (95% confidence interval 3.2%-102.4%). CONCLUSIONS: Results of this study revealed that hypoplastic vertebral artery was associated with new-onset posterior circulation infarction, and progression of basilar artery bending may serve as a potential intermediate factor in this association.