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Vertebral artery

Dr Yuranga Weerakkody and Dr Frank Gaillard et al.

The vertebral arteries eventually join to form the basilar artery, thus supplying the posterior fossa and occipital lobes.

Origin

The origin of the VA is usually from the subclavian arteries bilaterally, although it can be more proximal, along the brachiocephalic artery on the right, and to the aortic arch.

The ostium is the commonest site of stenosis.

When the origin is from the arch, then it is common for the artery to enter the foramen transversarium at a level higher than normal (C5 instead of C6).

Segments

The vertebral artery is typically divided into 4 segments.

V1 : origin to foramen transversarium (usually C6)
V2 : from the first foramen transversarium (usually C6) to the foramen transversarium of C2
V3 : from C2 to the dura
V4 : from the dura to their confluence to form the basilar artery.

V1 is located between longus colli (medially) and scalenus anterior (laterally) behind the common carotid artery. As it ascends it is crossed anteriorly by the inferior thyroid artery. On the left it is also crossed by the thoracic duct and on the right by the lymphatic duct. Posterior to the artery are the transverse process of C7, the inferior cervical ganglion and ventral rami of the seventh and eighth cervical spinal nerves.

V2 passes through the transverse foramina of the cervical vertebrae (usually C6 - C2).

V3 emerges from the transverse process of C2 (axis), and sweeps laterally to pass through the transverse foramen of C1 (atlas). From here it passes around the posterior border of the lateral mass of C1 and below the inferior border of the posterior atlanto-occipital membrane. Passing superomedially it pierces the dura.

V4 ascends anterior to the roots of the hypoglossal nerve (CN XII) and joins it contralateral counterpart at the lower border of the pons to form the basilar artery.

Branches

Numerous muscular branches are given off as the artery ascends, with relatively large ones passing posterior from V3 to supply the occipital triangle. They can anastamose with occipital branches of the ECA.

Spinal branches, pass into the vertebral canal via the intervertebral foraminae and contribute to supply not only of the vertebral bodies and extradural content of the canal, but also of the dura and spinal cord, reinforcing the anterior and posterior spinal arteries.

Variants

Size

left larger : 42%
right larger : 32%
same size : 26%

Right may terminate in PICA - which is usually dominant (ie small ipsilateral AICA).

The ostium is usually oriented cranially or posteriorly : (cranial ~ 47%; posterior ~ 44%; caudal ~ 6%; and anterior ~ 3% of the cases)

Egas Moniz performed the first vertebral angiography in 1933.

Summary

origin : branch of the subclavian artery
course :ascends posterior to the internal carotid artery in the transverse foramina of the cervical vertebrae
branches :
- numerous small branches
- spinal branches
termination : combines with the contralateral vertebral artery to form the basilar artery
key relationships : posterior to the internal carotid artery; ascends anterior to the roots of the hypoglossal nerve (CN XII)

Related pathology

References

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1. Ranganatha Sastry V, Manjunath KY. The course of the V1 segment of the vertebral artery. Ann Indian Acad Neurol 2006;9:223-6
2. Standring S. Gray's anatomy, the anatomical basis of clinical practice. Churchill Livingstone. (2008) ISBN:0443066841. Read it at Google Books - Find it at Amazon
3. Jinkins JR. Atlas of neuroradiologic embryology, anatomy, and variants. Lippincott Williams & Wilkins. (2000) ISBN:0781716527. Read it at Google Books - Find it at Amazon