A 71 year old woman presented with vertigo, nausea and vomiting.  Examination showed a left sided Horner's, left facial numbness; numbness over the right body; left sided ataxia, slurred speech, and weakness of the left soft palate.

(Top Left and Right) Axial Flair MRI of the lower medulla; (Bottom Left and Right) Corresponding diffusion weighted images of the scans above. Note the high signal in the lateral medulla and inferior cerebellum on the left. This is in the distribution of the posterior inferior cerebellar artery (PICA).  Infarctions of this artery result in Wallenberg's syndrome. The abnormal diffusion weighted images indicate that the lesion is acute.