Abstract Iatrogenic injury to the horizontal part of the third segment of the vertebral artery (V3h) is a catastrophic complication of the low retrosigmoid approach. This study aimed to delineate three-dimensional (3D) anatomical variations of the V3h through quantitative analysis and to establish an anatomical risk-stratification framework to improve surgical safety. A multimodal study was performed using 10 cadaveric specimens and 217 clinical computed tomography angiography (CTA) datasets.
