Infectious acute hemicerebellitis.

We report the case of a 5-year-old girl with initial symptoms of encephalitis who presented 24 hours later with hemiataxia, unilateral dysmetria, and hemiparesis. Brain magnetic resonance image (MRI) revealed a high T2-weighted signal in the ipsilateral hemicerebellar cortex. Forty-five days later, a second MRI disclosed signs of hemiatrophy and cortical gliosis. The clinical outcome was favorable, with only a slight lack of motor coordination in the involved hand remaining. Three other cases of hemicerebellitis have been reported in the literature, two of them presenting with hemicerebellar symptoms and one mimicking a tumor. Follow-up imaging studies some months later have shown hemiatrophy of the cerebellar cortex, except in one case with a normal control MRI. The pathophysiology of this unilateral involvement is difficult to explain. We underline the need to consider this rare entity in asymmetric cerebellar clinical presentations and to perform MRI rather than computed tomography to reach the correct diagnosis.