Anatomical variations of the vertebro-basilar system and their consequences on cerebral circulation

The intracranial portions of the vertebral arteries (VA), the basilar artery (BA), and their branches together form
the vertebrobasilar system (VBS). The vertebrobasilar system (VBS) is particularly important because it
supplies the posterior circulation of the brain [1,2]. The VBS supplies blood and glucose to the spinal cord
(medulla spinalis), brainstem (truncus cerebri), cerebellum, thalamus, inferior temporal lobe (pars inferior lobi
temporalis) and internal occipital lobe of the cerebellum (pars interna occipitalis cerebri [3,4,5] and is
responsible for vision, body coordination, body balance, consciousness and a large number of human
physiological functions. In this region, atherosclerotic manifestations with atheromatous plaques with extremely
serious consequences including artery blockage and cerebrovascular ischemia most often occur. Anatomical
variations of the VBS are numerous and a large number of them are benign. It is assumed that these anomalies
develop due to some errors during embryonic development. Clinically, the vertebral arteries (VA) are divided
into 4 segments. The first segment (V1) starts from its origin in the subclavian artery to the transverse process
of C6, the second segment (V2) from starts from C6 to the transverse process of C2, the third (V3) from C2 to
the foramen magnum, and the fourth (V4) forms the foramen magnum at the vertebrobasilar junction