Which imaging pattern is most consistent with a fairly acute stroke suitable for thrombolysis when onset is unclear?

Which imaging pattern is most consistent with a fairly acute stroke suitable for thrombolysis when onset is unclear?

• A. DWI positive with FLAIR positive
• B. DWI negative with FLAIR negative
• C. DWI positive with FLAIR negative
• D. Perfusion-diffusion mismatch only

Answer: (C)

The key idea here is using MRI signals to estimate when a stroke started in order to decide about thrombolysis when the exact onset time is unknown. Diffusion-weighted imaging (DWI) detects early cytotoxic edema within minutes of ischemia, so it becomes abnormal very soon after stroke onset. FLAIR signals, however, take several hours to become positive. When you see a pattern where DWI is abnormal but FLAIR is still negative, it suggests the stroke is fairly recent—likely within the time window where thrombolysis can be beneficial. This is why DWI-positive with FLAIR-negative is the best fit for unknown-onset thrombolysis: it implies the infarct is acute enough for reperfusion therapy. If both DWI and FLAIR are positive, the infarct is usually older than several hours, making thrombolysis less favorable. If both are negative, there may be no evident acute lesion on those sequences yet. Perfusion-diffusion mismatch reflects tissue at risk that could be saved, but it doesn’t as reliably indicate exact onset timing for unknown-onset treatment as the DWI-FLAIR mismatch does.

The key idea here is using MRI signals to estimate when a stroke started in order to decide about thrombolysis when the exact onset time is unknown. Diffusion-weighted imaging (DWI) detects early cytotoxic edema within minutes of ischemia, so it becomes abnormal very soon after stroke onset. FLAIR signals, however, take several hours to become positive. When you see a pattern where DWI is abnormal but FLAIR is still negative, it suggests the stroke is fairly recent—likely within the time window where thrombolysis can be beneficial.

This is why DWI-positive with FLAIR-negative is the best fit for unknown-onset thrombolysis: it implies the infarct is acute enough for reperfusion therapy. If both DWI and FLAIR are positive, the infarct is usually older than several hours, making thrombolysis less favorable. If both are negative, there may be no evident acute lesion on those sequences yet. Perfusion-diffusion mismatch reflects tissue at risk that could be saved, but it doesn’t as reliably indicate exact onset timing for unknown-onset treatment as the DWI-FLAIR mismatch does.