CTA-Based Vertebral-Level Origin, Transverse-Foramen Entry, and V1 Loop Morphology of the Vertebral Artery.

PURPOSE: This study evaluated proximal extracranial vertebral artery (VA) anatomy on computed tomography angiography (CTA), using three side-specific variables: vertebral level of arterial origin, transverse-foramen entry level, and V1 loop morphology. METHODS: Seventy-five CTA cases were reviewed, yielding 150 side-specific VAs. The vertical level of VA origin was classified from C6 to T3 according to vertebral-body thirds and intervening disc levels. Transverse-foramen entry level and V1 morphology were recorded separately for each side. V1 morphology was classified as no loop, single-direction loop, sequential multidirectional loop, combined loop, kink, coil, or fenestration; a single V2 loop recorded in the same field was tabulated separately. Bilateral combinations were analysed at the patient level. RESULTS: The VA arose from the subclavian artery in 143/150 arteries (95.3%) and from the aortic arch in 4/150 arteries (2.7%); the parent vessel was not recorded in 3/150 arteries (2.0%). The most frequent origin levels were the T1 middle third (35/150, 23.3%), T1 upper third (27/150, 18.0%), T1 lower third (26/150, 17.3%), and C7-T1 disc level (20/150, 13.3%). Entry into the transverse foramen occurred at C6 in 136/150 arteries (90.7%), C5 in 9/150 (6.0%), and C7 in 5/150 (3.3%). V1 loop or tortuosity types were identified in 102/150 arteries (68.0%); including a single fenestration and a single V2-segment loop, non-direct V1 configurations were present in 104/150 arteries (69.3%). Exact right-left V1 morphology was asymmetrical in 54/75 patients (72.0%). CONCLUSIONS: This CTA protocol provides a detailed side-specific and bilateral description of proximal extracranial VA anatomy by combining origin height, foraminal entry level, and V1 morphology.