The Vulnerable Conduit: Uncovering Segment-Specific Pathological Susceptibility and Bony Co-dependence of the Vertebral Artery in a South Indian Cohort.

Background The vertebral artery is a vital contributor to posterior cerebral circulation and demonstrates considerable anatomical variability due to its complex embryological development and close relationship with the cervical vertebrae. These variations have important clinical implications during cervical spine surgery, endovascular procedures, and in the assessment of vertebrobasilar insufficiency. However, comprehensive population-specific data on vertebral artery morphology in South Indians remain limited. The present study aimed to evaluate the anatomical variations, morphometric characteristics, and pathological associations of the vertebral artery using three-dimensional computed tomography angiography (3D-CTA) in a South Indian cohort, with special emphasis on segment-specific vulnerability and its relationship with the foramen transversarium. Methodology This retrospective observational study included CTA images of 151 adult patients (100 males and 51 females) obtained between December 2024 and March 2025. Three-dimensional volume-rendered and multiplanar reconstructed images were analyzed to assess vertebral artery origin, level of entry into the foramen transversarium, segment-wise diameter (V1-V4), vertebral artery hypoplasia (≤2 mm), foramen transversarium dimensions, and associated pathological changes. Measurements were independently reviewed by two radiologists. Statistical analysis was performed using SPSS version 19.0 (IBM Corp., Armonk, NA, USA), and a p-value <0.05 was considered statistically significant. Results Normal origin of the vertebral artery from the subclavian artery was observed in 95.4% of cases, while anomalous origin was identified in 4.6%. Entry into the foramen transversarium most commonly occurred at the C6 level (96.7%), with high or low entry levels observed in a small minority of cases. No significant association was found between vertebral artery origin and entry level. Segment-wise diameter analysis revealed no significant side-to-side or sex-based differences. The intracranial V4 segment demonstrated the largest mean diameter bilaterally and was the only segment showing significant variation across pathological categories (p = 0.033). Vertebral artery hypoplasia was present in 47.0% of cases, with a right-sided predominance. A significant positive correlation was observed between the diameter of the V4 segment and the corresponding foramen transversarium diameter on both sides (p = 0.0001), whereas no such correlation was found for the extracranial segments. Conclusions Although standard vertebral artery anatomy predominates in this South Indian cohort, clinically significant morphometric variations, particularly vertebral artery hypoplasia and intracranial segment vulnerability, are common. The observed correlation between V4 caliber and foramen transversarium dimensions highlights a developmental vascular-osseous interdependence. Although this study carries certain limitations, such as the retrospective nature of the study and the clinically referred cohort undergoing evaluation for cerebrovascular pathology, which may account for the higher observed prevalence of vertebral artery hypoplasia, these findings underscore the importance of detailed preoperative imaging to improve diagnostic accuracy and surgical safety in vertebrobasilar pathologies.