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Vertebral artery

The vertebral artery (VA) arises from the subclavian artery, ascends in the neck to supply the posterior fossa and occipital lobes as well as provide segmental vertebral and spinal column supply

Summary

Gross anatomy

Origin

The origin of the VA is usually from the posterior superior part of the subclavian arteries bilaterally, although the origin can be variable:

  • brachiocephalic artery (on the right)
  • aortic arch - 6% of cases

The VA is normally 3-5mm in diameter and the ostium is the most common 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 transverse foramen of C6
  • V2 - from the transverse foramen of C6 to the transverse foramen of C2
  • V3 - from C2 to the dura
  • V4 - from the dura to their confluence to form the basilar artery
Course
V1

V1 angles posteriorly between longus colli medially and scalenus anterior laterally behind the common carotid artery to enter the transverse foramen of C6. Relations:

  • anteriorly - common carotid artery, vertebral vein, thoracic duct (left VA) and lymphatic duct (right VA)
  • posteriorly - ventral rami of C7 and C8, transverse process of C7, inferior cervical ganglion
  • anteromedially - inferior thyroid artery, middle cervical ganglion
V2

V2 passes through the transverse foramina of the cervical vertebrae, normally C6 - C2. Here it is accompanied by vertebral veins and sympathetic nerves.

V3

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 lateral to the cervico-medullary junction. Passing superomedially it pierces the dura and arachnoid to continue as V4.

V4

V4 ascends anterior to the roots of the hypoglossal nerve (CN XII) and joins its 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.

Variant anatomy

  • asymmetry may due to hypoplasia, absence or termination into PICA of one of the vertebral arteries and is very common:
    • left dominant  ~45% (range 42-50%)
    • right dominant ~30% (range 25-32%)
    • co-dominant ~25% (range 25-26%)
  • complete or partial vertebral artery duplication
  • vertebral artery fenestration 
  • variable origin
    • aortic arch origin of left vertebral artery - incidence ~5% (range 3.1-8.3%)
    • may be the second (not first branch) of the subclavian artery
  • ostium may have variable orientation
    • cranial ~47%
    • posterior ~ 45%
    • caudal ~5%
    • anterior ~3%

Related pathology


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Neuroanatomy

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