In DW-MRI mismatch criteria for 6-24 hours, which core infarct volume range with NIHSS >20 and age <80 is considered?

• A. 1-9 mL
• B. 9-20 mL
• C. 31-51 mL with NIHSS >20 and age <80
• D. >100 mL

Answer: (C)

In the late-window approach to thrombectomy, treatment decisions hinge on how much brain is already infarcted (the core) versus how much tissue remains at risk (the penumbra), using diffusion-weighted imaging to define the core. Coupling this imaging information with clinical factors like how severe the deficit is (NIHSS) and the patient’s age helps identify who still has a meaningful amount of salvageable tissue.

For someone under 80 with a very large clinical deficit (NIHSS over 20), a diffusion-defined core in the range of about 31 to 51 mL indicates a substantial portion of tissue that is already infarcted but with a sizable amount still at risk that could be saved with reperfusion. This combination—moderate-to-large core but not an overwhelmingly large one, plus a high NIHSS and younger age—was used in trials to pick patients who benefited from mechanical thrombectomy even 6–24 hours after onset. That is why this core-volume range is the best fit for the scenario described.

Smaller cores with very high deficits and older ages, or cores exceeding roughly 100 mL, do not align with the criteria that demonstrated meaningful benefit in the late-window trials.