Schematic representation of the normal anatomy of the PSA and LSA systems, as well as some of their variations ( right side).Ī, The extradural and intradural segments of the vertebral artery (VA) are shown in dark and light gray, respectively. To illustrate the analogy between the 2 types of variants, and highlight some of their distinguishing features, each illustrated variant linked to the PSA system is matched with an equivalent variant derived from the LSA system. We propose that these variants are the result of variations in the development of the posterior spinal artery (PSA) rather than the LSA.
#PICA ARTERY ANATOMY SERIES#
We present a series of anatomic variants of the distal VA and PICA origins similar, but not identical, to the variants linked to the LSA system. 6 These authors showed, in particular, that anatomic variants such as the C1 and C2 origins of the PICA, the duplication of the VA, or the intradural course of the distal VA, are related to variations in size and connection of the LSA. Although the LSA was already identified by Kadyi in 1889, 5 its role in the developmental anatomy of the distal VA was only recognized later by Lasjaunias and colleagues. In the adult, the extracranial portion of this channel becomes the lateral spinal artery (LSA), a third longitudinal spinal arterial axis completing the anterior and posterior spinal axes at the upper cervical level. The latter 2 vessels, the PLBA and the lateral longitudinal artery, correspond, respectively, to the intracranial and extracranial portions of the same embryonic vascular channel. Among the embryonic precursors involved, particular attention needs to be given to the spinal branch of the proatlantal artery (ProA) (which corresponds, in fact, to the radicular artery of the first cervical nerve 5), the primitive lateral basilovertebral anastomosis of Padget (PLBA), and the lateral longitudinal artery of Moffat. This complex developmental anatomy was well described by Congdon 1 and Padget 2, 3 in human specimens and by Moffat 4 in the rat. The formation of the distal vertebral artery (VA) and its principal branch, the posterior inferior cerebellar artery (PICA), involves the combination of several embryonic vascular segments.
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.ĬONCLUSION: 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. 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. This study examined the possible role of another branch of the VA, the posterior spinal artery (PSA), in the development of similar vascular variations. 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).
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