OBJECTIVE: Surgical treatment in epilepsy is effective if the epileptogenic zone (EZ) can be correctly localized and characterized. Here we use simultaneous Electroencephalography-functional MRI (EEG-fMRI) data to derive EEG-fMRI and Electrical Source Imaging (ESI) maps. Their yield and their individual and combined ability to 1) localize the epileptogenic zone and 2) predict seizure outcome was then evaluated.
METHODS: Fifty-three children with drug-resistant epilepsy underwent EEG-fMRI. Interictal discharges were mapped using both EEG-fMRI haemodynamic responses and Electrical Source Imaging (ESI). A single localization was derived from each individual test (EEG-fMRI global maxima (GM)/ESI maxima) and from the combination of both maps (EEG-fMRI/ESI spatial intersection). To determine the localisation accuracy and its predictive performance the individual and combined test localisations were compared to the presumed EZ and to the postsurgical outcome.
RESULTS: Fifty-two/53 patients had significant maps; 47/53 for EEG-fMRI; 44/53 for ESI; 34/53 had both. The epileptogenic zone was well characterised in 29 patients; 26 had an EEG-fMRI GM localisation which was correct in 11; 22 patients had ESI localisation which was correct in 17; 12 patients had combined EEG-fMRI and ESI which was correct in 11.
Seizure outcome following resection was correctly predicted by EEG-fMRI GM in 8/20 patients, by the ESI maxima in 13/16. The combined EEG-fMRI/ESI region entirely predicted outcome in 9/9 patients including 3 with no lesion visible on MRI.
INTERPRETATION: EEG-fMRI combined with ESI provides a simple unbiased localisation that may predict surgery better than each individual test including in MRI-negative patients
