A 14-year-old boy had a 1-month history of diplopia (due to a VI nerve
palsy), motor ataxia and dizziness. Brain MRI showed a 1.5-cm mass po
sterior to the pens, Histopathological examination of a biopsy specime
n showed the lesion to be of viral origin. After 3 months, the ataxia
and dizziness had resolved and the MRI findings returned to normal. By
5 months the abducens paralysis had also resolved. Viral encephalitis
should be considered in the differential diagnosis of posterior fossa
tumours.