Extra- and Intracranial Vertebrobasilar Sector

Abstract

The vertebral artery (VA) originates from the subclavian artery. It runs posterosuperiorly behind the anterior scalene muscle, commonly reaching the foramen of the transverse process of the sixth cervical vertebra. This first segment of the VA has been called V1 (Huber 1979; Osborn 1999). The artery can enter the foramen at the inferior or superior level (Huber 1979). Furthermore, the artery runs vertically through the foramina of the transverse processes from C6 to C2 (the V2 segment), surrounded by the venous plexus. The spinal nerves lie behind. Between the foramina of C2 and C1, the artery curves laterally and somewhat anteriorly. Exiting from C1 begins the V3 segment, which curves backward, running in the sulcus of the posterior arch of C1; it then forms a second upward and forward curve and reaches the foramen magnum, where the artery penetrates the dura and forms its last segment (V4). It is conceivable that these curves protect the VA, allowing it to accommodate more easily movement in the atlanto-occipital region (Fig. 6.1).