Which artery originates from the internal carotid and is part of the circle of Willis, with collateral flow possible via the anterior communicating artery?

• A. MCA
• B. PCA
• C. ACA
• D. ICA

Answer: (C)

Understanding the Circle of Willis and how collateral flow works via the anterior communicating artery explains why the anterior cerebral artery is the correct pick. The internal carotid arteries feed the circle and give rise to the anterior cerebral arteries, which run on each side and are connected by the anterior communicating artery. This connection creates a cross-hemispheric channel, allowing collateral flow if one side is compromised. The middle cerebral artery is a lateral branch from the internal carotid, not the primary cross-connecting link in the circle, and the posterior cerebral artery is part of the posterior circulation connected via the posterior communicating artery, not through the anterior communicating route. The internal carotid artery is a feeder vessel, not one of the paired arteries that form the cross-communication.