Magnetic resonance imaging negative positron emission tomography positive temporal lobe epilepsy: FDG-PET pattern differs from mesial temporal lobe epilepsy

Purpose: Some patients with temporal lobe epilepsy (TLE) lack evidence of hippocampal sclerosis (HS) on MRI (HS-ve). We hypothesized that this group would have a different pattern of 2-deoxy-2-[F-18]fluoro-D-glucose (FDG)-positron emission tomography (PET) hypometabolism than typical mesial TLE/HS patients with evidence of hippocampal atrophy on magnetic resonance imaging (MRI) (HS+ve), with a lateral temporal neocortical rather than mesial focus. Procedures: Thirty consecutive HS-ve patients and 30 age- and sex-matched HS+ve patients with well-lateralized EEG were identified. FDG-PET was performed on 28 HS-ve patients and 24 HS+ve patients. Both groups were compared using statistical parametric mapping (SPM), directly and with FDG-PET from 20 healthy controls. Procedures: Thirty consecutive HS-ve patients and 30 age- and sex-matched HS+ve patients with well-lateralized EEG were identified. FDG-PET was performed on 28 HS-ve patients and 24 HS+ve patients. Both groups were compared using statistical parametric mapping (SPM), directly and with FDG-PET from 20 healthy controls. Results: Both groups showed lateralized temporal hypometabolism compared to controls. In HS+ve, this was antero-infero-mesial (T=17.13); in HS-ve the main clustering was inferolateral (T=17.63). When directly compared, HS+ve had greater hypometabolism inmesial temporal/ hippocampal regions (T=4.86); HS-ve had greater inferolateral temporal hypometabolism (T=4.18). Conclusions: These data support the hypothesis that focal hypometabolism involves primarily lateal neocortical rather than mesial temporal structures in 'MRI-negative PET-positive TLE.