A 17-YEAR-OLD GIRL had sudden onset of right hemiparesis and dysarthria. The patient had no significant medical history. She had transcortical sensory aphasia and severe right hemiparesis. Tendon reflexes were more brisk on the right side than on the left; the neurologic examination was otherwise normal. Cranial computed tomography showed a left parietal and frontal subcortical infarction. After an extensive workup, the mechanism of the infarct remained undetermined. Cranial magnetic resonance imaging performed 9 days after the ictus disclosed a left ischemic stroke involving the frontal and parietal subcortical areas (Figure 1, A and B). Hyperintensity on diffusion- and T2-weighted images (Figure 1, C-G) as well as hypointensity on T1-weighted images were present in the corticospinal tract, from the internal capsule to the medulla. Hyperintensity on fluid-attenuated inversion recovery (FLAIR) images was present from the internal capsule to the pons. Hypointensity was demonstrated in these areas on the apparent diffusion coefficient map, representing restriction to water diffusion.