A 68-year-old man presents to the emergency department 14 hours after last known well with acute left hemiparesis and aphasia. NCCT shows no hypodensity. CTA reveals occlusion of the right M1 segment. CT perfusion is performed, and the region marked **B** (preserved CBV with reduced CBF) is identified. Which of the following best describes the clinical significance of this finding and the most appropriate next management step?

Question

Accepted Answer

A. This represents the ischemic penumbra—viable tissue at risk of infarction; mechanical thrombectomy should be considered if core-penumbra mismatch criteria are met. ## Why option 1 is correct

The region marked **B** with preserved cerebral blood volume (CBV) despite reduced cerebral blood flow (CBF) is the ischemic penumbra—hypoperfused but potentially viable tissue. This CBV-CBF mismatch occurs because autoregulatory vasodilation maintains blood volume in the face of reduced flow. In the extended thrombectomy window (6–24 hours), identifying a penumbra with favorable core-penumbra mismatch (mismatch ratio ≥1.8, core <70 mL, penumbra >15 mL) is the cornerstone of patient selection for mechanical thrombectomy, as demonstrated in the DEFUSE 3 trial. The presence of a substantial penumbra indicates salvageable tissue that can be rescued by rapid reperfusion, making thrombectomy the standard of care in this extended window.

## Why each distractor is wrong

- **Option 2**: This describes the infarct core (matched CBV/CBF defect), not the penumbra. The penumbra is NOT irreversibly infarcted and is precisely the target for intervention.
- **Option 3**: Normal brain tissue would show preserved both CBF and CBV. The finding of reduced CBF rules out normal tissue, and the clinical context (M1 occlusion, acute stroke symptoms) confirms ischemia.
- **Option 4**: A matched CBV/CBF defect (region **C**) represents the core, not the penumbra. The penumbra is defined by the mismatch, not by matched defects.

**High-Yield:** Penumbra = preserved CBV + reduced CBF (mismatch); core = reduced both CBV and CBF (matched). Mismatch in the extended window = thrombectomy candidate.

[cite: AHA/ASA 2019 Stroke Guidelines; DEFUSE 3 Trial (Albers et al., NEJM 2018)]

Answer

B. This represents irreversibly infarcted tissue; thrombectomy is contraindicated and supportive care alone is recommended

Answer

C. This represents normal brain tissue with intact autoregulation; no intervention is needed

Answer

D. This represents matched CBV/CBF defect indicating completed infarction; only palliative measures are appropriate

Explanation

Why option 1 is correct

Why each distractor is wrong

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