Mapping of Anatomic Variants of the Proximal Vertebral Artery in Relation to Embryology

Quantification of the distance from the right SCA origin to the origin of the RVA. A, Sagittal MIPs show the origins of the RSCA (yellow arrow), defined as the distal wall of the origin of the right common carotid artery and the RVA (red arrow). B, Curved planar reformat shows a straightened SCA with estimation of the distance to the RVA origin along the SCA (black line indicates distance; yellow line, RSCA origin; red line, RVA origin).

RVA variants. RVA origin within 2 cm of the RSCA origin (white arrows) entering the FT (red arrows) at C3 (A), C4 (B), or C5 (C). D, The RVA originates from the distal aortic arch (white arrow), crosses along the upper thoracic vertebral bodies, and enters the FT at C7 (red arrow). Note that in this case, the left VA also enters the FT at C7 (green arrow), having originated as the fourth branch from the aortic arch (not shown).

Box-and-whisker plot showing the distance from the origin of the RSCA for right VAs entering the FT from C3 through C7. Although there is some overlap, high-entry VAs originate more proximally than arteries entering at C6. There is more heterogeneity in low-entry VAs, which may originate from the aortic arch (negative numbers on this figure) or along the RSCA. For this figure, all low-entry VAs are considered together, without regard for whether they share a common origin with the CCT.

LVA variants. LVA origin directly from the aortic arch, between the LCCA and LSCA origins (white arrows) entering the FT (red arrows) at C3 (A), C4 (B), or C5 (C). D, The LVA originates as the fourth branch from the arch (white arrow) and enters the FT at C7 (red arrow).

Multiple origins of the VAs. A, Two moieties originate proximally and distally along the LSCA. The moiety originating more distally (white arrow) at the expected VA origin enters the FT at C6 (red arrow), and the more proximal moiety (white arrowhead), originating within 2 cm of the RSCA, joins the first moiety at C4/C5 (red arrowhead), forming a fused artery that enters the FT at C4. This is the most common multiple-origin pattern. B, A similar pattern is noted on the left with the normal VA origin (white arrow), dominant in this case, entering the FT at C6 (red arrow) and the variant origin, originating from the arch between LCCA and LSCA (white arrowhead), joining at C4/C5 with a fused artery in the FT at C4 (red arrowhead). C, A rare subvariant, with 1 RVA moiety originating 8 mm from the right common carotid artery (not shown) and entering the FT at C3 (red arrowhead) and the other originating normally from the RSCA (white arrow) and entering at C6 (red arrow). D, An extremely rare variant, with the RVA having 3 origins, originating at 7, 11, and 14 mm along the RSCA and entering at C4 (red arrow), C5 (red arrowhead), and C6 (green arrow), respectively.

The origins of the VAs plotted against an idealized aortic arch. For this illustration, each VA origin was plotted in a 1D manner as a function of distance from the RSCA origin on the right or from the LSCA on the left. The position in any dimension other than that along the axis of the vessel is not based on anatomic data, and the distribution of vessel origins in the medial-lateral or craniocaudal dimension is used only to permit better visualization of the data points. Typical origins giving rise to VAs entering the FT at C6 are shown in white. Origins of vessels entering the FT at C3, C4, C5, and C7 are shown in purple, cyan, yellow, and red, respectively. Vessels originating along the posterior wall of the LSCA and entering at C7 are shown in red with a white outline. In addition, vessel origins entering at C7 whose vessel origin is shared with the CCT are shown in white with a red outline. Most of the high-entry vessels, which enter at C3–C5, originate in the proximal SCA on the right and directly from the arch or in the proximal subclavian artery on the left. Most of the low-entry vessels originate distal to or along the posterior wall of the LSCA in the region of the aortic isthmus.