Teaching NeuroImages: Acute crossed cerebellar diaschisis.

An 82-year-old woman with a history of chronic left parietal ischemic infarction presented with acutely altered mental status and abnormal right-sided movements. MRI (figure 1) demonstrated gyriform reduced diffusion signal, T2 hyperintensity, and swelling in the left cerebral hemisphere and contralateral right cerebellum. EEG (figure 2) revealed lateralized periodic discharges, likely representing seizure activity secondary to the chronic left parietal infarction. Acute crossed cerebellar diaschisis is hypothesized to result from excessive transmission of excitatory input from the seizing cortex to the contralateral cerebellum via the corticopontocerebellar pathways. This case illustrates the imaging manifestations of this uncommon but important clinical entity.