Vertebral artery

• Arises from subclavian artery.
• Enter the cervical spine at C6 transverse foramen in 90-95% and 5% in C7 foramen.
• Both vertebral arteries join at pontomedullary junction to form basilar artery.
• Has 4 segments:
  • V1 (Pre-foraminal):
    • From: Origin at the subclavian artery.
    • To: Entry into the C6 transverse foramen.
    • Courses upward between the longus colli and scalenus anterior muscles.
  • V2 (Foraminal):
    • From: C6 transverse foramen.
    • To: Exit at C2 transverse foramen.
    • Passes vertically through the transverse foramina of C6 to C2.
  • V3 (Atlantal/Extradural/Suboccipital):
    • From: Exit at C2.
    • To: Entry into dura mater at the foramen magnum.
    • Path: Loops laterally and posteriorly around the C1 posterior arch, then turns medially over the posterior atlanto-occipital membrane.
    • Highly variable in course and dominance.
  • V4 (Intradural/Intraventricular):
    • From: Penetration of the dura at the foramen magnum.
    • To: Union with the contralateral vertebral artery to form the basilar artery.
    • Supplies medulla, cerebellum (via PICA), and posterior cerebral circulation.
    • Vulnerable to dissection, aneurysm, or infarction.

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