Abstracts

Rationale: Malformations of Cortical Development (MCD) are frequently associated with drug-resistant epilepsy. Although increasingly recognized using high-resolution MRI and scalp EEG (typical dysplastic fast activity), localizing the epileptogenic zone (EZ) associated with MCD still relies on intra-cerebral EEG recordings. Our purpose was to study the spatial correlations between the modeled electrical sources of inter-ictal events (Irritative Zone = IZ) recorded with High-Resolution scalp EEG (HR-EEG) and the EZ defined by stereo-EEG (SEEG) in MCD. Methods: This prospective, bi-centric study enrolled 26 consecutive patients (22 in Nancy and 4 in Marseille) with established or suspected MCD undergoing pre-surgical investigations between 2008 and 2012 and comprising a HR-EEG (64-channels) with electrical source imaging and SEEG recordings. Results: Three patients were excluded from the analysis because of missing data (no SEEG seizure recording in two cases and no HR-EEG inter-ictal paroxysm registration in one case). The mean age at the time of SEEG recordings was 31 years. Nine patients had temporal lobe epilepsy, ten frontal lobe epilepsy and four posterior epilepsy including occipito-temporal or posterior parietal epilepsy. According to the ILAE Task Force consensus classification, seven patients had a type 1 or 2 focal cortical dysplasia (FCD Type I or II) and four had a type 3 focal cortical dysplasia (FCD Type III). Three had polymicrogyria associated with schizencephaly and nine patients (39.1%) were MRI negative. HR-EEG IZ and SEEG EZ were completely or more often partially overlapping in 95%. HR-EEG IZ co-localized with the EZ in 7 cases (30.4%) and four of them were MRI negative. In seven cases, the HR-EEG IZ comprised the entire EZ and extended to the propagation zone in 3/7. In six cases, HR-EEG IZ partially overlapped the EZ. In these cases, HR-EEG often identified at least a part of the propagation zone and often missed the medial part of the EZ. In 9 patients with negative MRI, HR-EEG correctly localized at least a part of the EZ. In 4/9, it allowed its precise localization and in 3/9, HR-EEG clearly influenced the SEEG electrodes position. Conclusions: HR-EEG combined with electrical source imaging helps to localize and target the EZ associated with established or suspected MCD particularly in MRI negative cases.