Illustrated Encyclopedia of Human Anatomic Variation: Opus II: Cardiovascular System: Arteries: Head, Neck, and Thorax
Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed
The left vertebral artery may arise directly from the left common carotid, or the root of the subclavian, close to the aortic arch. It may arise from the arch of the aorta. There are occasionally two left vertebral arteries. In one such case, one arose from the arch of the aorta, the other from the left subclavian artery in the normal position; the latter was smaller than normal.
The origin of the left vertebral artery from the aortic arch is a very common variation, but the origin of the vertebral artery from the right side of the arch is very rare indeed.
The frequency of the left vertebral artery arising from the aortic arch is:Pelligrini - Examined 104 specimens and noted the variation 3 times;
From these investigators, 563 specimens were studied and the vertebral artery arose from the left side of the aortic arch 10 times, or 1.79% of specimens studied.
The left and right vertebrals may be doubled with each vessel entering a different transverse foramen. In some instances, a left vertebral arises from the arch of the aorta between the origins of the left common carotid and the left subclavian; in one subject, the vertebral entered the foramen of the transverse process of the fifth cervical vertebra. The left vertebral in one case originated from the aorta at the upper angle of the junction of the left subclavian with the arch of the aorta; the vessel entered the transverse foramen of the fifth cervical vertebra. Either vertebral artery may enter the foramen in the second through seventh cervical vertebrae. When entering one of of the higher vertebral foramina, the artery may lie behind the common carotid. The vertebrals enter the sixth cervical foramen in 88% of cases and the seventh in 5% of cases; then ascends to enter the fifth cervical in 7% of cases.
Either vertebral artery may give rise to, or arise from, the inferior thyroid and may give origin to the superior intercostal, deep cervical, or occipital artery.
In 3% of cases, either artery may arise from the thyrocervical trunk or from the costocervical trunk.
Either artery may be much increased or diminished in size. The two vertebrals are usually unequal in size, the right being smaller than the left. The rule is not absolute, since Cruveilhier has reported seeing the left vertebral reduced to a small "twig" with the right being of normal caliber.
The inferior thyroid may lie behind (dorsal to) the vertebral artery.
Very rarely the two vertebrals fail to unite to form the median basilar artey, hence the basilar may appear to be doubled. The two longitudinal trunks may be united by anastomoses between them.
The vertebral artey may exist as several vessels that eventually unite, or it may form an arterial ring traversed by the hypoglossal nerve.
One of the anterior spinal branches (usually the left) is occasionally absent, in which case it is replaced by branches from the contralateral vertebral. Occasionally, a spinal branch arises to supply the cervical enlargement of the spinal cord.
The posterolateral spinal artery arises from the posterior inferior cerebellar in 73% of individuals and from the vertebral in about 20% of cases.
The following branches of the vertebral have been reported missing: the posterior inferior cerebellar, and the left anterior spinal, one of the posterior spinal arteries.
Branches of Vertebral
Anterior spinal. This artery arises from two small branches, which leave the vertebrals just before the vertebral unite to form the basilar.
Posterolateral spinal. This artery arises from the posterior inferior cerebellar in 73% of individuals or from the vertebral artery in 20% (Stopford).
Posterior Inferior Cerebellar. The largest branch of the vertebral leaves before the junction of the vertebrals to form the basilar artery. This artery may arise from the basilar or may be absent unilaterally.
In a study of the causes of variations in form and position of vertebral and basilar arteries, von Eichhorn suggested that atypical artery position and artery loops were more common in subjects of advanced age. The present authors know that carotid artery loops may be caused by pathology and this may be true in von Eichhorn's study as well. Additional study is required to settle this matter.
Image 10, Image 22, Image 95, Image 226A, Image 226B, Image 301, Image 417, Image 482
Anterior Median Longitudinal (of the Spinal Cord)
See Image 229, Image 416
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