The Vertebral Artery: A Systematic Review and a Meta-Analysis of the Current Literature.

(1) Background. The anatomical variations of the vertebral arteries (VAs) have a significant impact both in neurosurgery and forensic pathology. The purpose of this study was to evaluate the variational anatomy of the vertebral artery. We evaluated anatomical aspects regarding the V1 and V2 segments of the VA: origin, course, tortuosity, hypoplasia, and dominance, and established the prevalence of each variation. (2) Methods. We conducted a systematic search in PubMed and Google Scholar databases, up to December 2022. Sixty-two studies, comprising 32,153 vessels, were included in the current meta-analysis. We used a random-effects model with a DerSimonian-Laird estimator. The confidence intervals were set at 95%. The heterogeneity between studies was assessed using I. The funnel plot and Egger's regression test for plot asymmetry were used for the evaluation of publication bias. Statistical significance was considered at < 0.05. (3) Results. The most common site for the origin of both VAs was the subclavian artery. The aortic arch origin of the left VA had a prevalence of 4.81%. Other origins of the right VAs were noted: aortic arch (0.1%), right common carotid artery (0.1%), and brachiocephalic trunk (0.5%). Ninety-two percent of the VAs entered the transverse foramen (TF) of the C6 vertebra, followed by C5, C7, C4, and least frequently, C3 (0.1%). Roughly one out of four (25.9%) VAs presented a sort of tortuosity, the transversal one representing the most common variant. Hypoplasia occurred in 7.94% of the vessels. Left VA dominance (36.1%) is more common, compared to right VA dominance (25.3%). (4) Conclusions. The anatomy of the VA is highly irregular, and eventual intraoperative complications may be life-threatening. The prevalence of VA origin from the subclavian artery is 94.1%, 92.0% of the VAs entered the TF at C6, 26.6% were tortuous, and 7.94% were hypoplastic.