Anatomical structure of atlantoaxial segment of the vertebral artery and its clinical significance

Objective To observe the structure of the atlantoaxial segment of the vertevral artery and study the anatomical mechanism of extracerebral vertebral artery insufficiency. Methods Seventeen cadaveric head-neck specimens were used to observe the atlantoaxial segment of the vertebral artery and its surrounding structures, and special attention was given to how the surrounding structures affect the vertebral artery at head rotation. Results This portion of the vertebral artery has five curvatures in most of the specimens, and compensatory vascular expansion in the curvatures was found. Transverse foramen of the axis, C2 nerve root and the posterior atlantoaxial membrane contribute to secure the position of the vertebral artery by a tethering mechanism, and mechanical obstruction of the vertebral artery is liable to occur in such places as upper facet of the axis, lower facet of the atlas or transverse process of the atlas in case of atlantoaxial instability. Conclusion The morphological characteristics of the atlantoaxial portion of the vertebral artery and its surrounding structures can be the possible reason for the susceptibility of this portion of the vertebral artery to mechanical forces, and the tethering mechanism of the surrounding structures may play an important role in extracerebral vertebral artery insufficiency.