The DWI-FLAIR mismatch on MRI is used clinically to identify stroke patients who may benefit from thrombolysis when the time of onset is unknown. A positive mismatch (DWI positive, FLAIR negative) indicates:
- A The stroke likely occurred within the past 4.5 hours (within treatment window) ✓
- B The stroke occurred more than 24 hours ago
- C The penumbra has already infarcted
- D Haemorrhagic transformation has already occurred
Correct answer: A. The stroke likely occurred within the past 4.5 hours (within treatment window)
Explanation
DWI changes appear within minutes of ischemia, while FLAIR signal takes 4.5–6 hours to become abnormal. Therefore, DWI-positive/FLAIR-negative mismatch indicates that the infarct is likely <4.5 hours old, placing the patient within the treatment window for IV alteplase. The WAKE-UP trial demonstrated benefit of thrombolysis in DWI-FLAIR mismatch patients with unknown onset stroke. This allows treatment of 'wake-up strokes' where the actual onset time is unknown.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.