Electrical source imaging in cortical malformation-related epilepsy: A prospective EEG-SEEG concordance study

Objective Delineation of the epileptogenic zone (EZ) in refractory epilepsy related to malformations of cortical development (MCDs) often requires intracranial electroencephalography (EEG) recordings, especially in cases of negative magnetic resonance imaging (MRI) or discordant MRI and video-EEG findings. It is therefore crucial to promote the development of noninvasive methods such as electrical source imaging (ESI). We aimed to (1) analyze the localization concordance of ESI derived from interictal discharges and EZ estimated by stereo-EEG (SEEG); (2) compare the concordance of ESI, MRI, and electroclinical correlations (ECCs) with SEEG-EZ; and (3) assess ESI added value in the EZ localization. Methods We prospectively analyzed 28 consecutive patients undergoing presurgical investigation for MCD-related refractory epilepsy in 2009-2012. ESI derived from 64-channel scalp EEG was interpreted with blinding to, and subsequently compared with, SEEG-estimated EZ. Anatomic concordance of ESI with SEEG-EZ was compared with that of video-EEG and MRI. We further assessed ESI added value to ECC and MRI. Results Twelve patients (43%) had temporal and 16 (57%) had extratemporal epilepsy. MRI was negative in 11 (39%) and revealed a cortical malformation in 17 (61%). ESI was fully concordant with the EZ in 10 (36%) and partly concordant in 15 (53%). ECC presented a full and partial concordance with EZ in 11% and 82% of cases, respectively, and MRI in 11% and 46%, respectively. Of 11 patients with negative MRI, ESI was fully concordant with the EZ in 7 (64%) and partly concordant in 4 (36%). ESI correctly confirmed restricted or added localizations to ECC and MRI in 12 (43%) of 28 patients and in 8 (73%) of 11 patients with negative MRI. Significance ESI contributes to estimating the EZ in MCD-related epilepsy. The added value of ESI to ECC is particularly high in patients with MCD and negative MRI, who represent the most challenging cases for epilepsy surgery.