FALSE LATERALIZATION OF TEMPORAL-LOBE EPILEPSY WITH FDG POSITRON EMISSION TOMOGRAPHY

We report 2 patients in whom visual interpretation of interictal posit ron emission tomography (PET) with [F-18]fluorodeoxyglucose (FDG) sugg ested false lateralization of an epileptic focus. PET scans were inter preted as showing diffuse left temporal lobe hypometabolism in 1 patie nt and lateral temporal hypometabolism in the other. However, seizures began in the right mesial temporal lobe in both patients, and both re sponded favorably to right temporal lobectomy. In 1 patient, the intra cranial EEG showed continuous asymptomatic subclinical seizure activit y emanating from the right amygdala. These limbic discharges probably caused unrecognized right temporal lobe hypermetabolism. In the other case, quantitative analysis of metabolic rates showed conflicting mesi al and lateral metabolic indexes. Frequent mesial interictal discharge s might have increased lateral temporal metabolism. We conclude that a symptomatic epileptiform activity may alter temporal lobe metabolism a nd that quantitative PET analysis helps clarify contradictory visual P ET interpretations.