Abstracts

Rationale: Fluorodeoxyglucose-positron emission tomography (PET) is highly sensitive in localizing epileptogenic foci in combination with MRI and EEG in temporal lobe epilepsy (TLE) patients. Studies done in the past to understand the significance of extratemopral and subcortical hypometabolic regions included patients with mesial temporal lobe epilepsy (MTLE) only. The association of PET patterns with MRI, ictal and interictal EEG has not been studied collectively. Our objectives were: To assess the yield of PET in TLE patients, post-surgical outcome in patients that underwent anterior temporal lobectomy, predict factors associated with thalamic hypometabolism.Methods: Retrospective study of 39 patients with TLE that underwent long term EEG monitoring, MRI and PET. PET was analyzed visually by single reader. MRI was categorized into non-lesional (normal MRI) and lesional subgroup (abnormal MRI); latter further classified into mesial temporal lobe slcerosis (MTS) and miscellaneous category (cortical dysplasia, vascular malformation). Post-surgical outcome based on Engel classification was assessed. Inclusion criteria: Age range: 1-65 year, at least on 1 antiepileptic medication, seizure frequency > 3/year.Results: Of the 39 TLE patients; 20 had left temporal ictal EEG focus and 19 right temporal. PET focus was localized to ipsilateral temporal lobe in 26/39 (67%), bitemporal in 7/39 (18%), other focus in 4/39 (10%) and non specific in 2/39 (5%). Thalamic hypometabolism was seen in 20/39 (51%) patients (17/20 ipsilateral and 3/20 bilateral). 14/39 (36%) had normal MRI (non- lesional) and 25/39 (64%) had abnormal MRI (lesional) (44% MTS and 20% miscellaneous). A significant correlation of PET hypometabolism localization with interictal (p<0.001), and ictal EEG focus (p=0.034) in both lesional and non lesional subgroups was observed. In the non-lesional sub-group, relatively mild hypometabolism was seen in comparison to the lesional sub-group that had moderate to severe temporal hypometabolism (p= 0.006). Thalamic hypometabolism was noted preferentially in patients with moderate-severe temporal hypometabolism (p=0.039, OR 5.36) and with abnormal MRI (p=0.019)(image 2,1). However no correlation with age, duration of seizure history or seizure type was seen. Of the 12 patients that underwent surgery, 84% had excellent seizure control -Engel Class I, 8% had fair control (1-3 seizure per year) - Class II, and rest 8% with poor control -Class IV. Majority of the patients with excellent post-surgical outcome had focal temporal lobe hypometabolism only, compared to patients with poor control who had extratemporal hypometabolism. 11/12 patients that underwent surgery had thalamic hypometabolism.Conclusions: This study demonstrates significant efficacy of PET in localizing ictal focus in TLE patients even in those with normal MRI. The degree of focal PET hypometabolism can point towards a possible etiology. Thalamic hypometabolism is likely a secondary effect related to the severe temporal dysfunction. Extratemporal hypometabolism appears to be an indicator of poor post surgical outcome in TLE patients.