Positron emission tomography in Rasmussen's encephalitis.

This report presents unusual positron emission tomography findings in an 11-year-old male with Rasmussen's encephalitis. This patient underwent fluorine-18 fluorodeoxyglucose positron emission tomography to localize his ictal focus before surgical consideration. Positron emission tomography disclosed marked hypermetabolism in the left cerebral hemisphere and basal ganglia with subnormal right cerebral activity and crossed cerebellar diaschisis. The heterogeneous distribution of metabolism suggests a combination of areas in different stages of ictal and postictal involvement. The hypermetabolic region in the left hemisphere was larger in size and extent (now including the left frontoparietal lobe) than the sole hypermetabolic left temporal lobe on his positron emission tomography from 2 years ago. While this positron emission tomography pattern of progression appears most commonly in Rasmussen's encephalitis case studies, few serial reports exist. The complex positron emission tomography findings of this case emphasize the importance of knowing the history of recent seizures, seizure type, clinical status at time of injection, and electroencephalographic correlation before interpreting functional neuroimaging studies. Finally, positron emission tomography studies can help clarify whether patients with Rasmussen's encephalitis with dominant hemisphere involvement are appropriate candidates for surgery or not.