Abstracts

RATIONALE: To investigate the relation of metabolic asymmetry in temporal lobe epilepsy (TLE) studied with Positron Emission Tomography (PET) to electroencephalographic seizure onset origin. METHODS: 18F-FDG-PET was performed on 58 patients with refractory TLE (age 15-50 years; 28 women). All patients had surface ictal video EEG and 36 of 58 underwent invasive EEG for additional seizure localization. Based on EEG onset localization, seizures were classified into two groups; 1)lateral or basal lateral and 2)mesial or mesiobasal temporal origin. Quantitative PET data analysis and normalized metabolic rates (NR) were obtained using the Region of Interest template previously described. We calculated asymmetry indices (AI) in the inferior lateral temporal (ILTAI) and inferior medial temporal(IMTAI)regions using the formula (contralateral NR-ipsilateral NR)/[(contralateral NR+ipsilateral NR)/2]. We used the Wilcoxon rank-sum test to determine the effect of seizure localization on the AIs. RESULTS: Thirty three patients had lateral or basal lateral (LT) seizure onset and 25 had mesial or mesial basal (MT) onset. In LT patients, ILTAI was 0.181?0.025 (mean?SEM) and IMTAI was 0.111?0.016. In MT patients, ILTAI was 0.210?0.028 and IMTAI was 0.148?0.022. The differences between patient groups were not statistically significant. Results were not different in the subgroup with localization by intracranial EEG. CONCLUSIONS: There is no clear cut relation between PET metabolic asymmetry and EEG seizure localization. PET can lateralize but not localize foci within the temporal lobe.