The location of the primary motor cortex can be detected in healthy adults using the findings of ‘T2 hypointensity’ and the ‘double layer sign’ on 3 T diffusion-weighted imaging. The aim of this study was to assess whether ischemic involvement of the primary motor cortex can be identified on 3 T diffusion-weighted imaging within six-hours after stroke onset and to evaluate whether this finding could predict clinical outcome three-months after ischemic stroke.

Sixty-five patients who had paralysis and ischemia of the anterior circulation underwent 3 T magnetic resonance imaging within six-hours of symptom onset. Follow-up MRI was obtained at 72 h. Anatomic localization and ischemic involvement of the primary motor cortex were evaluated on diffusion-weighted imaging by two investigators. Ischemic involvement on the primary motor cortex was classified into three grades. Ischemic lesion volumes were measured. We compared the favorable outcomes at three-months between subjects with and without ischemic involvement on the primary motor cortex using the NIHSS and modified Rankin Scale.

Ischemic involvement on the primary motor cortex was identified in 52% of patients. Interrater agreement coefficients were 0·93 for the identification of ischemic involvement of primary motor cortex. As defined by scores on the modified Rankin Scale, among the patients with ischemic involvement of the primary motor cortex were worse than the patients without ischemic involvement of the primary motor cortex (P = 0·01). The mean ischemic lesion volume at baseline diffusion-weighted imaging was 38·7 ± 41·7 cm3 and was 89·8 ± 93·6 cm3 at follow-up T2-WI. Ischemic involvement on the primary motor cortex (odds ratio: 14·7) was a determinant for worse outcome.

3T diffusion-weighted imaging can identify ischemic involvement on the primary motor cortex and may provide useful information for predicting outcome during the hyperacute stage. Ischemic involvement on the primary motor cortex has a significant negative impact on recovery.