II. Anatomy: Background

  1. Circle of Willis forms a collateral communication between the Anterior Circulation and the Posterior Circulation
  2. Anterior segment of Circle of Willis
    1. Middle Cerebral Artery (bilateral)
    2. Anterior Cerebral Artery (bilateral)
    3. Anterior Communicating Artery (single, midline)
      1. Connects anterior cerebral arteries together
  3. Posterior segment of Circle of Willis
    1. Posterior Cerebral Artery (bilateral)
    2. Basilar Artery (single, midline)
  4. Interconnection between anterior and posterior segments
    1. Posterior communicating arteries (bilateral)
      1. Connects each Internal Carotid Artery to Basilar Artery
  5. Function
    1. Not all patients have a complete Circle of Willis
    2. Redundant Blood Flow in case of cerebral Occlusion
    3. Normal conditions (no Occlusion)
      1. Anterior and posterior communicating arteries typically carry little flow
    4. Arterial Occlusion (Cerebrovascular Accident)
      1. Arterial pressure falls in the occluded circulation
      2. Pressure gradient favors collateral flow across the communicating arteries

III. Anatomy: Goldberg's Circle of Willis Analogy to a Cartoon Spider

  1. Background
    1. Stephen Goldberg , MD describes a brilliant memory aid for the Circle of Willis
    2. Cartoon Spider (named Willis) represents the cerebral Vascular Anatomy
    3. Anatomy is as if viewed from below
      1. Looking up at the inferior brain surface (Brainstem, pons and Optic Chiasm)
  2. Top of Willis head
    1. Anterior Cerebral Artery
    2. Anterior Communicating Artery
  3. Willis Face
    1. Optic Chiasm (eye brows)
    2. Internal Carotid Artery (eyes)
    3. Middle Cerebral Artery (?antenna)
    4. Pituitary Gland (nose)
    5. Mammilary Body (mouth)
    6. Posterior Communicating Artery (jaw line)
  4. Willis Arms
    1. Posterior Cerebral Artery
    2. Cranial Nerve 3 (axilla)
    3. Superior Cerebellar Artery
  5. Willis Body
    1. Pons (trunk)
    2. Basilar Artery (spine)
  6. Willis Legs
    1. Anterior Inferior Cerebellar Artery
    2. Vertebral Artery
    3. Posterior Inferior Cerebellar Artery
  7. Willis Genitalia
    1. Anterior Spinal Artery (penis)
  8. Images
    1. http://lifeinthefastlane.com/a-spider-called-willis/
  9. References
    1. Goldberg (2014) Clinical Neuroanatomy, Medmaster, p. 6-15

IV. Anatomy: Images Circle of Willis

  1. neuroCvCircleWillisGrayBB516.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  2. neuroCvCircleWillisGrayBB519.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)

V. References

  1. Gilman (1989) Manter and Gatz Essentials of Neuroanatomy and Neurophysiology, Davis, p. 216-21
  2. Goldberg (2014) Clinical Neuroanatomy, Medmaster, p. 6-15
  3. Netter (1997) Atlas Human Anatomy, ICON Learning, p. 130-9

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