Developmental anatomy of the distal vertebral artery in relationship to variants of the posterior and lateral spinal arterial systems

Abstract

Background and purpose: A certain number of anatomic variants involving the distal vertebral artery (VA) are explained by variations in size and connection of the lateral spinal artery (LSA). This study examined the possible role of another branch of the VA, the posterior spinal artery (PSA), in the development of similar vascular variations.

Materials and methods: Four types of variations in the distal VA, including the C1 and C2 origins of the posterior inferior cerebellar artery (PICA), the duplication of the distal VA, and the aberrant course of the distal VA, are illustrated by 9 angiographic observations.

Results: For each type of VA variant listed above, examples resulting from variations in size and connection of the LSA and PSA could be matched.

Conclusion: Variation in size and connection of the PSA is at the origin of a set of anatomic variations of the distal VA similar, but not identical, to the vascular variants linked to the LSA.

Fig 1.

A proximal origin (C1) of the right PICA (PSA type) in a 20-year-old woman. A, DSA, right VA, anteroposterior view, showing a proximal origin of the right PICA from the superior aspect of the right VA. The PICA trunk has a Z-shaped course consistent with the normal course of a PSA. From a developmental perspective, the segment of the VA proximal to the takeoff of the PICA corresponds to the spinal branch of the ProA, which divides into an anterior radicular branch (the distal VA), and a posterior radicular branch (the PSA). In this case, the ascending ramus of the PSA (white arrow), which normally only establishes a small anastomosis with the PICA, is prominent and constitutes the actual origin of this vessel. B, DSA, right VA, lateral view, showing the dorsal position of the proximal PICA in the foramen magnum region (black arrow), aligned with the ascending ramus of the PSA (white arrow).

Fig 2.

A double proximal origin of the right PICA (LSA type) in a 15-year-old boy. A, DSA, right VA, anteroposterior view, showing a double origin of the right PICA from the right LSA via C1 (white arrowhead) and C2 (black arrowhead) roots. Note the location of the PICA origin from the inferior aspect of the VA, consistent with a variation of the LSA. B, DSA, right VA, lateral view, showing the ascending course of the proximal PICA (white arrow) aligned with the LSA (black arrow). The proximal PICA has a more anterior position in the region of the foramen magnum (compare with Fig 1B), consistent with the course of the LSA.

Fig 3.

A proximal (C1) origin of the left PICA (PSA type) in a 47-year-old woman, as demonstrated by a 3D reconstruction of a rotational angiogram with simultaneous osseous and vascular rendering. This technique is known as 3D fusion DSA (3D-FDSA) (Infinix NB, Toshiba, Japan). A, 3D-FDSA, left VA, lateral view, showing that the proximal portion of the PICA follows the typical course of a PSA trunk as described by Maillot and Koritke (ie, a first segment closely paralleling the distal VA, followed by a sharp caudal and dorsal curve that brings the vessel in a posterior-lateral position within the foramen magnum). The ascending ramus of the PSA (white arrow) then continues as the proximal portion of the PICA. B, 3D-FDSA, left VA, superior axial view, demonstrating the posterior location of the PICA within the foramen magnum. The topographic correspondence between the adult distal VA and PSA/PICA, and the embryonic ventral and dorsal radicular branches of C1 is well illustrated.

Fig 4.

A proximal (C2) origin of the right PICA (PSA type) in a 44-year-old woman. A, DSA, right VA, anteroposterior view, showing the C2 origin of the right PICA (black arrowhead, partially masked by teeth subtraction artifacts). B, DSA, right VA, lateral view, showing the posterior position of the PICA at the foramen magnum (black arrowhead). The PICA is the cranial continuation of the posterior spinal axis (black arrow), fed by a segmental C2 branch. Note the more anterior position of the LSA (white arrow).

Fig 5.

A proximal (C2) origin of the left PICA (LSA type) in a 44-year-old woman (figure shown flipped horizontally for comparison with Fig 4). A, DSA, left VA, anteroposterior view, showing a proximal (C2) origin of the left PICA (black arrowhead). B, DSA, left VA, lateral view, showing that the left PICA (white arrowhead) is the cranial continuation of the LSA (white arrow), with which it is aligned. Compared with Fig 4B, the PICA crosses the foramen magnum in a more anterior position consistent with the LSA rather than the PSA.

Fig 6.

Duplication of the distal right VA (PSA type) in a 47-year-old woman. A, DSA, right VA, anteroposterior view, showing a duplication of the distal VA consisting, in fact, of a double origin of the right PICA from the PSA (C1 origin, white arrow) and from the V4 segment of the VA (normal origin, white arrowhead). The LSA is indicated by black arrowheads. B, DSA, right VA, lateral view, also showing a duplication of the distal VA consisting of a double origin of the right PICA from the PSA (C1 origin, white arrow) and from the V4 segment of the VA (normal origin, white arrowhead).

Fig 7.

Duplication of the distal left VA (LSA type) in a 52-year-old woman. A, DSA, left VA, anteroposterior view (flipped horizontally for comparison with Fig 6A), showing a dominant intradural segment (black arrowhead) corresponding to the LSA with a prominent C2 root (white arrow). The normal distal VA is slightly hypoplastic (white arrowheads). B, DSA, right VA, unsubtracted lateral view. As with Fig 7A, this variant also shows a dominant intradural segment (black arrowhead) corresponding to the LSA with a prominent C2 root (white arrow).

Fig 8.

An aberrant course of the distal right VA (PSA type) in a 64-year-old woman. A, DSA, right VA, anteroposterior view. This variant is similar to the VA duplication shown in Fig 7, with a double origin of the PICA from the PSA (white arrow) and from the distal VA (white arrowhead). The difference between the 2 variants lies in the absence of a segment of the right VA between the 2 PICA origins, resulting in a seemingly “aberrant” course of the VA. B, DSA, right VA, lateral view. As with Fig 8A, this variant is also similar to the VA duplication shown in Fig 7, with a double origin of the PICA from the PSA (white arrow) and from the distal VA (white arrowhead).

Fig 9.

A 58-year-old woman with an aberrant course of the distal right VA (LSA type). DSA, right VA, anteroposterior view, showing the intradural course of the distal VA that is, in fact, a prominent segment of the LSA (white arrow). Note the presence of a very small vascular channel corresponding to the real distal VA (white arrowhead).

Fig 10.

Schematic representation of the normal anatomy of the PSA and LSA systems, as well as some of their variations (right side). A, The extradural and intradural segments of the vertebral artery (VA) are shown in dark and light gray, respectively. The PSA originates from the extradural VA and parallels its course before bifurcating into a descending posterolateral ramus (the PSA per se), and an ascending ramus joining the PICA. The latter may become a variant origin of the PICA. The anterior spinal artery (ASA) is also shown. B, The C1 origin of the PICA (PSA type). The anastomosis between the ascending ramus of the PSA and the PICA is prominent, and the PSA serves as the actual origin of the PICA. C, A distal VA duplication of the PSA type, in which the true distal VA is paralleled by a supernumerary vascular segment that branches off the PICA. The relative size of the 2 limbs can vary. If the true distal VA is markedly diminutive or absent, the variant becomes an aberrant course of the VA (PSA type). D, The LSA is the most lateral of the 3 cervical spinal axes. It establishes several segmental connections with the VA (C1-C4) as well as a cranial anastomosis with the PICA. E, The C1, C2, and C3 origins of the PICA (LSA type). The rostral anastomosis of the LSA with the PICA is prominent, and any of the lateral segmental connections of the LSA with the VA may serve as a PICA origin, alone or in combination. F, A duplication of the distal VA of the LSA type. This time, the true VA is cranial to the supernumerary limb, which is made of a prominent LSA segment. If the true distal VA is markedly diminutive or absent, the variant becomes an aberrant course of the VA (LSA type).