The Circle of Willis is an arterial anastomosis at the base of the brain. A 65-year-old patient has internal carotid artery occlusion; which communicating artery is primarily responsible for maintaining ipsilateral anterior circulation?

• A Posterior communicating artery, allowing basilar artery flow to maintain all of the anterior circulation
• B Ophthalmic artery, providing retrograde flow from the external carotid via the supraorbital route
• C Anterior communicating artery, allowing contralateral anterior cerebral artery to supply the occluded side via cross-filling ✓
• D Middle cerebral artery perforators from the lenticulostriate arteries

Explanation

The anterior communicating artery (AComA) connects the two anterior cerebral arteries, allowing contralateral anterior cerebral artery territory to fill the ipsilateral ACA territory when the ipsilateral internal carotid artery is occluded. This is the most important collateral for ICA occlusion, demonstrated on angiography as cross-filling. The posterior communicating artery (PComA) connects the posterior cerebral artery to the ICA; it supplements posterior circulation to anterior, not the primary compensatory vessel in ICA occlusion. AComA aneurysms are the most common intracranial aneurysm location (30–35%), likely related to increased hemodynamic stress in this compensatory vessel.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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