Vertebral artery (VA)

V1 segment

Arises from subclavian artery. Runs posterosuperior behind the anterior scalene muscle to enter the C6 transverse foramen.

V2 segment

Runs through the transverse foramina from C6 to C2.

V3 segment

Extends from when the vertebral artery exits the transverse foramen of C1 to foramen magnum where it penetrates the dura and enters the subarachnoidal space.


The cervical segments (V1-3) of VA give off segmental, cervical muscular and spinal branches throughout their course. Muscular branches supply various muscles of the cervical region. Spinal branches supply the spinal nerve roots, dura and bone structures of the cervical spine and anastomose with the anterior and posterior spinal arteries.


Multiple anastomoses with branches from external carotid artery and cervical arteries are common:

  • From the occipital artery, typically at C1-2 levels
  • From the ascending pharyngeal artery via its hypoglossal branch, usually at C3 level and intracranially
  • From the deep cervical artery typically at C3-4 levels
  • From the ascending cervical artery at C5-7 levels

V4 - Intracranial segment

Runs intradurally behind the clivus. Unites with contralateral VA near the pontomedullary junction to form the basilar artery.


Branches:
  1. Perforating branches
    • Small arteries arising from the posterior surface of the VA. They supply the inferior and middle portions of the anterolateral medulla.

  1. Posterior inferior cerebellar artery (PICA)
    • Arises from the intradural segment of VA and sometimes from the extradural segment. Runs anterolaterally. Surrounds the cerebellar tonsil and divides into vermian and hemispheric branches.
    • Supplies:
      • Choroid plexus of the 4th ventricle
      • Lateral and posterior medulla oblongata
      • Inferior vermis and cerebellar tonsils
      • Inferior surface of cerebellar hemisphere

  1. Anterior spinal artery
    • Arises distal to the PICA. Sometimes has unilateral origin. Along its course it receives anastomosing branches from the VA, the ascending cervical artery, the inferior thyroid artery, the intercostal arteries in the thorax and the lumbar, iliolumbar and lateral sacral arteries.
    • Supplies:
      • Median-paramedian part of inferior medulla oblongata
      • Anterior aspect of spinal cord

  1. Posterior spinal artery
    • Usually arises from the PICA but can originate directly from the VA. Below medulla oblongata, the artery forms an extensive anastomotic pial network of vessels which also anastomose extensively with the radicular artery branches around the posterior roots.
    • Supplies:
      • Posterior inferior part of medulla oblongata
      • Posterior columns of the spinal cord

Anatomic variants

  • Hypoplastic VA ending as PICA
  • PICA arising extradurally
  • Large PICA supplying contralateral hemisphere.
  • Hypoplastic or absent PICA replaced by a large AICA
  • Origin of VA from the aortic arch distal to the subclavian artery
  • Thoracic origin of VA from common trunk with thoracic intercostal arteries (very rare)
  • Fenestration of the BA, VA or rarely, PICA: division of the vessel into two separate parallel channels which rejoin distally
  • True duplication of BA
  • Duplication of VA extracranial segment, usually at C1-C2 level