Mesiobasal versus lateral temporal lobe epilepsy: metabolic differences in the temporal lobe shown by interictal 18F-FDG positron emission tomography.

Metabolic abnormalities in the temporal lobe (TL) of 25 patients suffering from temporal lobe epilepsy of mesiobasal or lateral TL origin have been investigated using interictal [18F]-fluorodeoxyglucose (FDG) positron emission tomography (PET). The epileptogenic area was determined by ictal EEG recordings using foramen ovale and scalp electrodes in 20 patients, and by the use of stereo-electroencephalography in one patient. Four patients with structural lesions on their MRIs had noninvasive ictal surface EEG recordings. Sixteen patients had a clear-cut mesiobasal seizure onset, and in five patients the seizures originated from the lateral temporal neocortex. Twenty-four patients underwent selective surgery. Patients with temporal limbic seizures associated with mesial gliosis (n = 15) had the lowest FDG uptake in the entire TL, followed by patients with lateral temporal seizure origin (n = 5). Patients with tumors located in the mesiobasal TL (n = 5) showed, in general, only a slight decrease of glucose metabolism in all TL structures. There was no clear-cut correlation between the degree of hypometabolism and the location of EEG-defined epileptogenic focus. The metabolic pattern, however, differed between the patient groups and allowed a discrimination between patients of mesial temporal and lateral temporal seizure onset.