Understanding the Circle of Willis

Jun 3, 2024

Understanding the Circle of Willis

Key Feeder Vessels

  • Internal Carotid Artery:
    • Feeds into the anterior part of the Circle of Willis.
  • Vertebral Artery:
    • Feeds into the posterior part of the Circle of Willis.

Orientation

  • Right Cerebral Hemisphere, Right Cerebellum
  • Left Cerebral Hemisphere, Left Cerebellum
  • Inferior view of Circle of Willis

Pathway from Vertebral Arteries

Vertebral Arteries

  • Supplied from the subclavian arteries
  • Pass through transverse foramina of cervical vertebrae
  • Run through suboccipital triangle before foramen magnum

Key Branches and Fusion

  • Posterior Inferior Cerebellar Artery (PICA):
    • Important branches from vertebral arteries
  • Posterior Spinal Arteries:
    • Branches off PICA
  • Anterior Spinal Artery:
    • Formed by branches from vertebral arteries fusing
  • Basilar Artery:
    • Fusion of vertebral arteries
    • Runs through to the pons and midbrain

Branches from Basilar Artery

  • Anterior Inferior Cerebellar Artery (AICA):
    • Branches off at the base of the basilar artery
  • Labyrinthine Arteries (Internal Acoustic Arteries):
    • Branch off near the cerebellum
  • Pontine Branches:
    • Multiple branches feeding the pons
  • Superior Cerebellar Arteries:
    • Supply the top of the cerebellum
  • Posterior Cerebral Arteries:
    • P1 (proximal) and P2 (distal) segments

Posterior Communicating Arteries

  • Connect basilar system to the anterior circulation pathway

Internal Carotid Artery Branches

Initial Branches

  • Ophthalmic Artery:
    • First branch off internal carotid

Middle Cerebral Artery

  • Major continuation from the internal carotid
  • Anterior Choroidal Artery:
    • Important branch off middle cerebral
  • Lenticulostriate Arteries:
    • Supply internal capsule, lentiform nucleus

Anterior Cerebral Artery

  • A1 Segment: Proximal
  • A2 Segment: Distal

Anterior Communicating Artery

  • Important for collateral circulation

Key Points

  • Circle of Willis is a crucial anastomotic system
  • Ensures collateral circulation to prevent ischemia
  • Vulnerable to occlusions and aneurysms

Next Steps

  • Study cerebral ischemic strokes due to occlusions or aneurysms of these vessels