The topography and significance of extratemporal hypometabolism in refractory mesial temporal lobe epilepsy examined by FDG-PET.

PURPOSE

This study aims to map the temporal and extratemporal 18-fluorodeoxyglucose positron emission tomography (FDG-PET)-defined hypometabolism in mesial temporal lobe epilepsy (MTLE). We hypothesize that quantitative analysis will reveal extensive extratemporal glucose hypometabolism (EH), that the EH is related to seizure propagation beyond the temporal lobe, hypometabolism restricted to one temporal lobe predicts a good outcome following surgery, and EH predicts a poor outcome.

METHODS

Sixty-four patients were studied who had undergone temporal lobectomy for intractable MTLE and had at least 2 years of postoperative follow-up. Spatial preprocessing and statistical analysis on preoperative interictal FDG-PET using statistical parametric mapping (SPM 2) identified significant regions of hypometabolism compared to normal controls. The predictors of outcome were determined by univariable and multiple logistic regression analyses.

RESULTS

EH was common and widespread, occurring most frequently in the ipsilateral insula and frontal lobe. The extent of EH was not significantly associated with age of onset or the duration of epilepsy. Presence of secondarily generalized tonic--clonic seizures (SGTCS) was associated with a larger extent of remote hypometabolism (RH, p < 0.005). Multiple logistic regression analysis identified the extent of RH and the age at surgery as independent predictors of seizure outcome.

DISCUSSION

Our results indicate that RH in MTLE is associated with a poorer surgical outcome, especially if seen in the contralateral hemisphere. The extent of RH relates to SGTCS but not to duration of epilepsy.