Origin-entry geometry and left-sided V1 vertebral artery tortuosity: a retrospective cross-sectional CT angiography study.

PURPOSE: V1 vertebral artery (VA) tortuosity is associated with cervical artery dissection, stent fracture, and endovascular access difficulty, and predominates on the left; its anatomical basis and its relationship to VA dominance have not been quantitatively tested on CT angiography (CTA). METHODS: Bilateral V1 morphometric analysis was performed on 50 cervical CTAs (24 men, 26 women; 63.2 ± 15.5 years). The tortuosity index (TI) was computed as the centreline-to-straight-line length ratio; VA dominance was determined at two segmental levels. RESULTS: Left V1 was more tortuous than right (TI 1.37 ± 0.26 vs. 1.20 ± 0.15; Wilcoxon p < 0.0001; d_z = 0.74) in 82% of patients. TI correlated with age (Spearman ρ = 0.599, p < 0.001 for left; ρ = 0.439, p = 0.001 for right) but not with sex, and showed no association with calibre-based dominance (p = 0.53). A more cranial VA origin was associated with higher TI (Spearman ρ = -0.64, p < 0.001 for left; ρ = -0.37, p = 0.009 for right) and remained a significant predictor in multivariable linear regression adjusted for age and sex (left V1 β = -0.0408 per ordinal step toward a more caudal origin, 95% CI - 0.0683 to - 0.0133, p = 0.005) against a conserved bilateral C6 transverse-foraminal entry (76%). We refer to this configuration as the origin-entry mismatch. CONCLUSION: Left-sided V1 tortuosity was associated with an origin-entry geometric mismatch; no association with calibre-defined dominance was detected.