Pseudotumoral acute hemicerebellitis in a child.

Acute cerebellitis is an inflammatory disorder usually involving both sides of the cerebellum and presenting with localized signs such as ataxia. Hemicerebellitis is extremely rare in children and may clinically and radiologically resemble a tumor. There are very few reports of hemicerebellitis needing decompressive surgery. We report a case of hemicerebellitis in a 15 year old child presenting with severe headache but no cerebellar symptoms whose brain CT revealed an ill-defined mass compressing the fourth ventricle (pseudotumoral). MRI of the posterior fossa revealed a swollen left cerebellar hemisphere, supra-tentorial hydrocephalus and tonsil herniation, without any cerebral or brain stem lesions. Due to worsening symptoms she required a decompressive craniectomy, and the biopsy revealed an inflammatory process, possibly viral. At follow-up she was asymptomatic and the MRI revealed only slight cerebellar atrophy. This case had an atypical clinical presentation and illustrates that though a self-limited evolution is expected, surgical intervention may be needed in acute cerebellitis.