[A case of brainstem encephalitis diagnosed by stereotactic biopsy].

Brainstem encephalitis is a rare form of encephalitis which should be differentiated from cerebrovascular and neoplastic diseases. The authors report a case of viral brainstem encephalitis mimicking malignant lymphoma. A 55-year-old female was admitted to our hospital with gradually progressive diplopia and left hemiplegia. CT scan revealed low density lesions in the right globus pallidus and the anterior limb of the internal capsule. MRI demonstrated high intensity signals extending into the right cerebral peduncle, temporal lobe, thalamus and the contralateral thalamus on FLAIR images. Petechial hemorrhages were seen in the affected lesions, but no enhancement was observed following administration of a contrast material. CSF examination revealed mild mononuclear cell dominant pleocytosis. Both early and delayed images of 123I-IMP SPECT revealed marked hot spots corresponding to the lesions on FLAIR images. CT-guided stereotactic biopsy was useful for early diagnosis.