3 Tesla MRI-negative focal epilepsies: Presurgical evaluation, postoperative outcome and predictive factors

•3 Tesla MRI is the gold standard for defining true MRI-negative focal epilepsies.•Favorable postoperative seizure outcome has been achieved in 65% of patients.•FDG-PET and intracranial EEG contributed decisively to favorable outcome.•Congruent unilateral FDG-PET hypometabolism is favorable predictive factor in TLE. To investigate presurgical diagnostic modalities, clinical and seizure outcome as well as predictive factors after resective epilepsy surgery in 3 Tesla MRI-negative focal epilepsies. This retrospective study comprises 26 patients (11 males/15 females, mean age 34±12years, range 13–50 years) with 3 Tesla MRI-negative focal epilepsies who underwent resective epilepsy surgery. Non-invasive and invasive presurgical diagnostic modalities, type and localization of resection, clinical and epileptological outcome with a minimum follow-up of 1year (range 1–11 years, mean 2.5±2.3years) after surgery as well as outcome predictors were evaluated. All patients underwent invasive video-EEG monitoring after implantation of intracerebral depth and/or subdural electrodes. Ten patients received temporal and 16 extratemporal or multilobar (n=4) resections. There was no perioperative death or permanent morbidity. Overall, 12 of 26 patients (46%) were completely seizure-free (Engel IA) and 65% had a favorable outcome (Engel I–II). In particular, seizure-free ratio was 40% in the temporal and 50% in the extratemporal group. In the temporal group, long duration of epilepsy correlated with poor seizure outcome, whereas congruent unilateral FDG-PET hypometabolism correlated with a favorable outcome. In almost two thirds of temporal and extratemporal epilepsies defined as “non-lesional” by 3 Tesla MRI criteria, a favorable postoperative seizure outcome (Engel I–II) can be achieved with accurate multimodal presurgical evaluation including intracranial EEG recordings. In the temporal group, most favorable results were obtained when FDG-PET displayed congruent unilateral hypometabolism.