A 58-year-old man with hypertension presents to the emergency department 8 hours after acute onset of left hemiparesis and aphasia. Non-contrast CT head shows no hemorrhage. CT perfusion is performed. The region marked **A** in the diagram shows decreased cerebral blood flow (CBF) with preserved cerebral blood volume (CBV) and prolonged mean transit time (MTT). Which of the following best describes the pathophysiological basis for this perfusion pattern and its clinical significance?

Question

Accepted Answer

D. Cerebral autoregulation has maintained arteriolar vasodilation to preserve CBV despite reduced inflow, identifying salvageable penumbral tissue that may benefit from mechanical thrombectomy. ## Why option 1 is right

The region marked **A** demonstrates the pathognomonic perfusion signature of the ischemic penumbra: preserved or increased CBV with decreased CBF. This mismatch occurs because cerebral autoregulation responds to reduced arterial inflow by triggering downstream arteriolar vasodilation, which increases cerebral blood volume while flow remains compromised. This tissue is electrically silent but metabolically viable—the definition of salvageable penumbra. Per the AHA/ASA 2019 guidelines and the DAWN and DEFUSE-3 trials, identification of this CBV-CBF mismatch with prolonged MTT/Tmax is the cornerstone of patient selection for mechanical thrombectomy in the extended window (6–24 hours), where a mismatch ratio ≥1.8 and absolute mismatch ≥15 mL with core <70 mL predicts benefit from reperfusion therapy.

## Why each distractor is wrong

- **Option 2**: This describes the infarct core (region **B**), where both CBV and CBF are markedly decreased, indicating exhausted autoregulation and irreversible cell death. The preserved CBV in region **A** explicitly rules out this pattern.
- **Option 3**: Luxury perfusion (region **D**) occurs in chronic or reperfused tissue where metabolic demand has decreased; it would show increased CBV with increased or normal CBF, not decreased CBF. This does not apply to acute ischemia with reduced inflow.
- **Option 4**: Collateral failure would result in primary CBF reduction followed by CBV reduction (the core pattern), not preservation of CBV. The preserved CBV in region **A** indicates intact autoregulatory response, not collateral failure.

**High-Yield:** CBV-CBF mismatch = penumbra = salvageable tissue = thrombectomy window extended to 24 hours if core <70 mL and mismatch ratio ≥1.8.

[cite: AHA/ASA Stroke Guidelines 2019; DAWN, DEFUSE-3 trials]

Answer

A. Collateral circulation has failed, resulting in primary reduction of CBV with secondary reduction in CBF, indicating completed infarction

Answer

B. Complete exhaustion of autoregulatory mechanisms has resulted in simultaneous reduction of both CBV and CBF, indicating irreversible infarction

Answer

C. Luxury perfusion syndrome has developed due to loss of metabolic demand, resulting in increased CBV without corresponding increase in CBF

Explanation

Why option 1 is right

Why each distractor is wrong

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