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

Abstract

Interictal electrical source imaging (ESI) encompasses a risk of false localization due to complex relationships between irritative and epileptogenic networks. This study aimed to compare the localizing value of ESI derived from ictal and inter-ictal EEG discharges and to evaluate the localizing value of ESI according to three different subgroups: MRI lesion, presumed etiology and morphology of ictal EEG pattern. We prospectively analyzed 54 of 78 enrolled patients undergoing pre-surgical investigation for refractory epilepsy. Ictal and inter-ictal ESI results were interpreted blinded to-and subsequently compared with stereoelectroencephalography as a reference method. Anatomical concordance was assessed at a sub-lobar level. Sensitivity and specificity of ictal, inter-ictal and ictal plus inter-ictal ESI were calculated and compared according to the different subgroups. Inter-ictal and ictal ESI sensitivity (84% and 75% respectively) and specificity (38% and 50% respectively) were not statistically different. Regarding the sensitivity, ictal ESI was never higher than inter-ictal ESI. Regarding the specificity, ictal ESI was higher than inter-ictal ESI in malformations of cortical development (MCD) (60% vs. 43%) and in MRI positive patients (49% vs. 30%). Within the ictal ESI analysis, we showed a higher specificity for ictal spikes (59%) and rhythmic discharges > 13 Hz (50%) than rhythmic discharges < 13 Hz (37%) and (ii) for MCD (60%) than in other etiologies (29%). This prospective study demonstrates the relevance of a combined interpretation of distinct interictal and ictal analysis. Inter-ictal analysis gave the highest sensitivity. Ictal analysis gave the highest specificity especially in patients with MCD or a lesion on MRI.

Personalized Deep Learning based Source Imaging Framework Improves the Imaging of Epileptic Sources from MEG Interictal Spikes

“…In terms of sublobar sensitivity and specificity, there is a tradeoff between the two metrics depending on the properties of the source imaging methods evaluated. For more diffused imaging methods, a sublobar sensitivity of 84%-98% and specificity of 38%-60% can be reached, and the geometric mean of the sensitivity and specificity is in the range of 56% -77% [66,67] . When using sparse imaging methods for a higher spatial specificity value, the sensitivity could drop to 25%-40% [62].…”

Intracerebral Correlates of Scalp EEG Ictal Discharges Based on Simultaneous Stereo-EEG Recordings

“…The morphology of the first ictal abnormality on scalp EEG was classified as follows: “artifact” (when EEG was blurred by muscle artifacts), “low-voltage fast activity” (LVFA) if frequency ≥30 Hz and amplitude <25 μV, “rhythmic fast activity” (RFA) if ≥ 13 Hz and <30 Hz, “rhythmic slow activity” (RSA) if < 13 Hz (with a subdivision into alpha [8–12 Hz], theta [4–7 Hz], and delta [<4 Hz] discharge), “suppression” if amplitude <10 μV, 27 “periodic activity,” “sharp wave,” and “slow wave.” Lateralization was collected as ipsilateral, contralateral to the EZ in SEEG, or bilateral. The scalp EEG localization was categorized as follows: Fz, Cz, Pz, Oz, Fp2F4-Fp1F3, F4C4-F3C3, P4-P3, O2-O1, F8T8Ft10-F7T7Ft9, P8P10-P7P9.…”

Diagnostic and therapeutic approaches in refractory insular epilepsy

“…As an estimation of the brain source of an electrical potential field, electrical source imaging (ESI) based on high‐density EEG can help to correctly localize ictal or interictal insular discharges, 42 as well as interictal ESI based on low‐density EEG 43 . Frequent discharges are more commonly found with FCD, which is the most common lesion at the origin of insular epilepsy 14 …”

“…36 In insular epilepsies, scalp EEG allows, at most, the lateralization of the EZ rather than its localization, 11 and suggests a deep source in the case of a rhythmic slow-wave ictal pattern. 41 As an estimation of the brain source of an electrical potential field, electrical source imaging (ESI) based on high-density EEG can help to correctly localize ictal or interictal insular discharges, 42 as well as interictal ESI based on low-density EEG. 43 Frequent discharges are more commonly found with FCD, which is the most common lesion at the origin of insular epilepsy.…”