Low-density scalp electrical source imaging of the ictal onset zone network using source coherence maps

Abstract

Introduction: This study investigated low-density scalp electrical source imaging of the ictal onset zone and interictal spike ripple high-frequency oscillation networks using source coherence maps in the pediatric epilepsy surgical workup. Intracranial monitoring, the gold standard for determining epileptogenic zones, has limited spatial sampling. Source coherence analysis presents a promising new non-invasive technique.

Methods: This was a retrospective review of 12 patients who underwent focal resections. Source coherence maps were generated using standardized low-resolution electromagnetic tomography and concordance to resection margins was assessed, noting outcomes at 3 years post-surgery.

Results: Ictal source coherence maps were performed in 7/12 patients. Six of seven included the surgical resection. Five of seven cases were seizure free post-resection. Interictal spike ripple electrical source imaging and interictal spike ripple high-frequency oscillation networks using source coherence maps were performed for three cases, with two of three included in the resection and all three were seizure free.

Discussion: These findings may provide proof of principle supporting low-density scalp electrical source imaging of the ictal onset zone and spike ripple network using source coherence maps. This promising method is complementary to ictal and interictal electrical source imaging in the pediatric epilepsy surgical workup, guiding electrode placement for intracranial monitoring to identify the epileptogenic zone.

Keywords: electrical source imaging; epilepsy surgery; ictal onset zone; low density; source coherence maps.

Figure 1

Concordant Localization of Ictal ESI Source Coherence, Interictal HFO ESI and Interictal HFO Source Coherence to Resection Margins, for ILAE Class 1 Patient, alongside MEG and FDG PET scans (Case 2). Patient underwent a lesionectomy of a right post-central gyrus lesion. (A) Ictal ESI Source Coherence Map localizing to the right pre-central and post-central gyrus. (B) Interictal HFO ESI localizing to the right post-central gyrus. (C) Interictal HFO Source Coherence map identifying a network localizing to the right parietal, central and temporal regions. (D) sLORETA source localization through ICA, clipped at 75%. (E) FDG-PET scans identifying a region of hypometabolism within the right post-central gyrus. (F) Interictal MEG Dipole Cluster localizing to the right frontal, temporal, and parietal regions. (G) T1 MRI Images of Post-Operative Resection Margins with Coronal, Sagittal and Axial views.

Figure 2

Summary Diagram: Concordance of Pre-Surgical Work-Up, ESI and Source Coherence Localization to the Potential Epileptogenic Zone (resection). Patients are indicated by their corresponding case number. The epileptogenic zone was defined as the resected region in seizure-free patients after three years. Numbers overlapping with the potential epileptogenic zone (resection) indicate concordant imaging results, which were established if the irritative zone or ictal onset zone was localized within the surgical resection margins. Those outside the potential epileptogenic zone indicate discordant results. A table on the left indicates a list of cases without test results for each diagnostic modality.