On DWI-MRI obtained 2 hours after acute stroke onset, an area in the right MCA territory shows restricted diffusion. On PWI (perfusion-weighted imaging), a larger area of reduced cerebral blood flow is noted. The DWI-PWI mismatch represents:
- A Ischemic penumbra — at-risk but potentially salvageable tissue ✓
- B Completed infarct core with surrounding luxury perfusion
- C Vasogenic edema surrounding the infarct
- D Hemorrhagic transformation of infarct
Explanation
The DWI-PWI mismatch concept is fundamental to acute stroke imaging: DWI bright region represents the irreversibly infarcted core (cytotoxic edema with restricted diffusion), while the larger PWI-affected region represents total ischemic territory. The mismatch zone (PWI > DWI) is the ischemic penumbra — tissue with critically reduced perfusion but not yet irreversibly damaged, potentially salvageable by thrombolysis or thrombectomy if treated promptly. This mismatch is the physiological basis for extending thrombolysis window to 4.5 hours and thrombectomy to 24 hours in selected patients (DAWN/DEFUSE-3 criteria).
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.