Regarding the arterial anatomy of the Circle of Willis, all of the following statements are correct EXCEPT:

Explanation

## Arterial Components of the Circle of Willis **Key Point:** The Circle of Willis is an arterial anastomosis at the base of the brain formed by specific vessels. Understanding which arteries form it and their relationships is essential. ### Correct Statements | Component | Relationship | Correct? | |-----------|--------------|----------| | Anterior communicating artery | Connects both ACAs (anterior cerebral arteries) | ✓ Yes | | Posterior communicating artery | Connects ICA to PCA (not a continuation) | ✓ Yes | | Posterior cerebral arteries | Terminal branches of basilar artery | ✓ Yes | | Circle completion | Anterior (AComm) + Posterior (PComm) | ✓ Yes | ### Why Option 1 Is Wrong **High-Yield:** The posterior communicating artery (PComm) is **NOT** a direct continuation of the internal carotid artery. Rather, it is a **connecting vessel** that arises from the terminal portion of the ICA and joins it to the posterior cerebral artery (which arises from the basilar artery). The ICA continues as the middle cerebral artery (MCA) and anterior cerebral artery (ACA). **Clinical Pearl:** This distinction is clinically important because occlusion of the PComm does not interrupt the main flow of the ICA; collateral circulation through the Circle of Willis can maintain cerebral perfusion. ### Anatomical Summary The Circle of Willis comprises: - **Anteriorly:** ACA (right) → AComm → ACA (left) - **Laterally:** ICA → MCA (main continuation) - **Posteriorly:** ICA → PComm → PCA (from basilar) **Mnemonic:** **AIPPA** — Anterior (AComm), Internal carotid (ICA), Posterior (PComm/PCA), Posterior (PCA), Anterior (ACA) — traces the circle's path. [cite:Standring Anatomy 42e Ch 27]