The Circle of Willis

Overview

• Provides blood supply to the brain.
• Connects two arterial sources to form an arterial circle, supplying the brain with blood.

Arterial Sources

• Internal Carotid Arteries
  • Arise from the common carotid artery.
  • Bifurcate into external and internal carotid arteries.
• Vertebral Arteries
  • Arise from the first part of the subclavian artery.
  • Run through the transverse foramina of the cervical vertebrae.

Anatomy of the Circle of Willis

• Located at the base of the brain around the optic chiasm and hypothalamus.
• Internal Carotid Artery
  • Divides to form:
    • Middle Cerebral Artery (runs in lateral sulcus)
    • Anterior Cerebral Artery (runs in interhemispheric fissure)
  • Ophthalmic Artery branches off after passing into the cranial cavity.
  • Posterior Communicating Artery connects to posterior cerebral artery.

Branches and Connections

• Anterior Cerebral Artery
  • Runs in the interhemispheric fissure.
  • Anterior Communicating Artery connects the left and right anterior cerebral arteries.
• Middle Cerebral Artery
  • Runs in the lateral sulcus.
  • Supplies the striate arteries for the basal ganglia.
• Posterior Cerebral Artery
  • Connects via the posterior communicating artery.

Blood Supply Territories

• Anterior Cerebral Artery
  • Supplies medial and superior lateral aspects of cerebral hemispheres.
• Middle Cerebral Artery
  • Supplies lateral aspect of the brain.
• Posterior Cerebral Artery
  • Supplies occipital lobes and inferior parts of the brain.

Vertebrobasilar System

• Basilar Artery
  • Formed by union of vertebral arteries.
  • Runs in front of the pons.
  • Terminates by dividing into posterior cerebral arteries.
• Branches of Vertebrobasilar System
  • Superior Cerebellar Artery
  • Anteroinferior Cerebellar Artery
  • Posteroinferior Cerebellar Artery (arises from vertebral arteries)
  • Pontine Arteries
  • Anterior and Posterior Spinal Arteries

Communication Between Circulations

• Posterior Communicating Artery connects anterior (internal carotid) and posterior (vertebral-basilar) circulations.

Conclusion

• The Circle of Willis is a critical structure providing a collateral blood supply to the brain, connecting different arterial systems and ensuring consistent perfusion.