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II. Normal Vascular Anatomy

A. Arterial Supply and Anastomoses

The brain receives its blood supply from paired vertebral and internal carotid arteries as well as from anastomotic channels derived from extracranial vessels. You should be familiar with the pattern of arterial supply in the brain.

  Anastomotic Channels

  • Circle of Willis (via anterior communicating and posterior communicating arteries) – most important
  • Channels between external and internal carotid arteries, especially via the ophthalmic artery.
  • Leptomeningeal anastomoses between peripheral branches of the anterior, middle and posterior cerebral arteries

B. Venous Drainage

The veins of the brain drain into the dural venous sinuses and through them to the internal jugular veins. Since the surface veins of the brain have abundant anastomoses of large caliber, localized venous obstructions may produce few effects. Because the veins of the CNS are valveless, blood may flow in or out of the skull through these connections, providing a potential route for infection.