Localizing value of electrical source imaging: Frontal lobe, malformations of cortical development and negative MRI related epilepsies are the best candidates

Abstract

ObjectiveWe aimed to prospectively assess the anatomical concordance of electric source localizations of interictal discharges with the epileptogenic zone (EZ) estimated by stereo-electroencephalography (SEEG) according to different subgroups: the type of epilepsy, the presence of a structural MRI lesion, the aetiology and the depth of the EZ.MethodsIn a prospective multicentric observational study, we enrolled 85 consecutive patients undergoing pre-surgical SEEG investigation for focal drug-resistant epilepsy. Electric source imaging (ESI) was performed before SEEG. Source localizations were obtained from dipolar and distributed source methods. Anatomical concordance between ESI and EZ was defined according to 36 predefined sublobar regions. ESI was interpreted blinded to- and subsequently compared with SEEG estimated EZ.Results74 patients were finally analyzed. 38 patients had temporal and 36 extra-temporal lobe epilepsy. MRI was positive in 52. 41 patients had malformation of cortical development (MCD), 33 had another or an unknown aetiology. EZ was medial in 27, lateral in 13, and medio-lateral in 34. In the overall cohort, ESI completely or partly localized the EZ in 85%: full concordance in 13 cases and partial concordance in 50 cases. The rate of ESI full concordance with EZ was significantly higher in (i) frontal lobe epilepsy (46%; p = 0.05), (ii) cases of negative MRI (36%; p = 0.01) and (iii) MCD (27%; p = 0.03). The rate of ESI full concordance with EZ was not statistically different according to the depth of the EZ.SignificanceWe prospectively demonstrated that ESI more accurately estimated the EZ in subgroups of patients who are often the most difficult cases in epilepsy surgery: frontal lobe epilepsy, negative MRI and the presence of MCD.

Respective Contribution of Ictal and Inter-ictal Electrical Source Imaging to Epileptogenic Zone Localization

“…Simultaneous scalp and SEEG studies also proved that IID recorded in scalp electrodes could match with inter-ictal activity generated in cortical areas related to but outside of the EZ (Alarcon et al 1994;Koessler et al 2015). In previous ESI studies, we also demonstrated that localizing sources from IID encompasses a significant risk of localizing outside the EZ (Rikir et al 2014;Abdallah et al 2017).…”

“…to standard pre-surgical evaluation (Knowlton et al 2009;Beniczky et al 2013;Rikir et al 2014;Abdallah et al 2017). Most of them used inter-ictal discharges (IID) for source localization (Gavaret et al 2004(Gavaret et al , 2006(Gavaret et al , 2009Brodbeck et al 2011) because these discharges are easier to record during a limited period of time, have a higher signal-to-noise ratio (SNR), and are less susceptible to be contaminated by muscle and movement artifacts.…”

Ictal and interictal electric source imaging in pre‐surgical evaluation: a prospective study

“…Of 20 cases of normal or non‐localizable II‐EEG, IC‐ESI could correctly localize the source in 11 patients who became seizure‐free after surgery. Concordance between ESI and ICR was 52–72%, consistent with previous studies (60–82%) . In our series, concordance with ICR results was best for II‐ECD (72%).…”

Coregistrating magnetic source and magnetic resonance imaging for epilepsy surgery in focal cortical dysplasia

“…An interesting target for future research would be to investigate (and compare to MSI results) electric source imaging (ESI) specifically for FCD II, including high-density EEG (HD-ESI). Some studies using ESI for localizing diagnostics for epilepsy surgery did include FCD patients ( Abdallah et al, 2017 , Russo et al, 2016 , Lascano et al, 2016 , Rikir et al, 2014 , Brodbeck et al, 2011 ). From these reports, that did include quite heterogenous etiologies, it seems that ESI can be particularily successful in FCD II-related epilepsies.…”