A 58-year-old man with hypertension and smoking history presents to the emergency department with acute-onset left-sided weakness and speech difficulty. Non-contrast CT head shows no hemorrhage. CTA of the Circle of Willis is performed for stroke workup. The structure marked **C** in the diagram is noted to be patent and demonstrates normal caliber. Which of the following is the PRIMARY clinical significance of assessing the patency of this vessel in acute ischemic stroke management?

Explanation

## Why "It is a common site of large vessel occlusion amenable to mechanical thrombectomy, and its patency helps determine candidacy for thrombectomy" is right The posterior communicating artery (PCOM, marked **C**) is a critical component of the Circle of Willis and serves as a collateral pathway between the anterior and posterior circulations. In acute ischemic stroke, CTA assessment of the PCOM is essential to identify large vessel occlusions (LVO) — particularly at the distal ICA, MCA M1, and basilar artery — which are the primary targets for mechanical thrombectomy. The PCOM's patency indicates preserved collateral flow and helps determine candidacy for thrombectomy in the extended window (up to 24 hours in selected patients with favorable imaging on DEFUSE-3 and DAWN trials). This assessment directly informs the modern stroke pathway: clinical NIHSS + non-contrast CT (rule out bleed) + CTA (LVO detection) + CT perfusion (penumbra assessment) → decision for tPA and/or thrombectomy. (Harrison 21e Ch 426; Sutton Radiology) ## Why each distractor is wrong - **"It is the most common location for berry aneurysm formation..."**: While the PCOM is indeed a site of berry aneurysm formation (ACOM > PCOM > MCA bifurcation in frequency), the primary clinical role of CTA in acute stroke is LVO detection, not aneurysm screening. Aneurysm assessment is secondary in the acute stroke pathway. - **"It is the primary collateral pathway from anterior to posterior circulation..."**: Although the PCOM does provide collateral flow between anterior and posterior circulations, it is not the "primary" pathway — the vertebral arteries and basilar artery are the main posterior circulation supply. The PCOM's role is as a communicating vessel, not the primary supply. - **"It is the rate-limiting step in cerebral autoregulation..."**: The PCOM has no role in cerebral autoregulation; this is a physiologic mechanism involving arteriolar resistance. Additionally, while intracranial atherosclerotic disease (ICAD) is prevalent in Asian populations including India, the PCOM is not the rate-limiting step in this process — the intracranial ICA and MCA are more commonly affected. **High-Yield:** In acute ischemic stroke, CTA of the Circle of Willis is the KEY imaging for large vessel occlusion detection; PCOM patency indicates preserved collateral circulation and supports thrombectomy candidacy within extended windows (DAWN, DEFUSE-3 up to 24 hours). [cite: Harrison 21e Ch 426; Sutton Radiology]