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

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).

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.

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.

Left-sided V1 tortuosity was associated with an origin-entry geometric mismatch; no association with calibre-defined dominance was detected.