Circle of Willis (Cerebral Arterial Circle)
This critical anastomotic network ensures collateral blood flow to the brain if one of the major supply arteries is occluded. Understanding its anatomical components is high-yield for localizing vascular lesions.
1. Components
- Anterior System: Internal Carotid Arteries (ICA) → Anterior Cerebral Artery (ACA) and Middle Cerebral Artery (MCA).
- Posterior System: Vertebral Arteries → Basilar Artery → Posterior Cerebral Arteries (PCA).
- Connecting Vessels: Anterior Communicating Artery (ACom) and Posterior Communicating Artery (PCom).
2. Clinical Correlation (Aneurysms)
| Artery Site | Common Presentation |
|---|---|
| ACom | Bitemporal hemianopsia (compression of the optic chiasm). |
| PCom | CN III palsy (dilated pupil, ptosis, “down and out” eye). |
| MCA | Contralateral hemiparesis/sensory loss (face/arm > leg). |
NEET PG Hint: Remember that the MCA is the most common site for stroke. If you see a patient with a sudden onset “thunderclap” headache, think **Subarachnoid Hemorrhage (SAH)**, often caused by a ruptured berry aneurysm at the bifurcation of the ACom or PCom.