Electrical source imaging for presurgical focus localization in epilepsy patients with normal MRI

Abstract

PURPOSE: Patients with magnetic resonance (MR)-negative focal epilepsy (MRN-E) have less favorable surgical outcomes (between 40% and 70%) compared to those in whom an MRI lesion guides the site of surgical intervention (60-90%). Patients with extratemporal MRN-E have the worst outcome (around 50% chance of seizure freedom). We studied whether electroencephalography (EEG) source imaging (ESI) of interictal epileptic activity can contribute to the identification of the epileptic focus in patients with normal MRI. METHODS: We carried out ESI in 10 operated patients with nonlesional MRI and a postsurgical follow-up of at least 1 year. Five of the 10 patients had extratemporal lobe epilepsy. Evaluation comprised surface and intracranial EEG monitoring of ictal and interictal events, structural MRI, [(18)F]fluorodeoxyglucose positron emission tomography (FDG-PET), ictal and interictal perfusion single photon emission computed tomography (SPECT) scans. Eight of the 10 patients also underwent intracranial monitoring. RESULTS: ESI correctly localized the epileptic focus within the resection margins in 8 of 10 patients, 9 of whom experienced favorable postsurgical outcomes. DISCUSSION: The results highlight the diagnostic value of ESI and encourage broadening its application to patients with MRN-E. If the surface EEG contains fairly localized spikes, ESI contributes to the presurgical decision process

Prognostic factors for seizure outcome in patients with MRI-negative temporal lobe epilepsy: A meta-analysis and systematic review

“…Most of the included studies used PET, scalp EEG and invasive EEG (subdural EEG, depth EEG or stereotactic EEG). Two studies used ictal SPECT [12,17] or electrical source imaging [12] to localize the focus. Both subgroups of comparison were from the same patient cohort, without controlling for usage of postoperative antiepileptic drugs, different surgery approaches or perioperative complications, which may influence the postoperative seizure outcome.…”

“…Several studies have attempted to identify the prognostic factors for seizure-free outcome after surgery in MRI-negative TLE patients, including age, epilepsy duration, pathology, and fluorodeoxyglucose positron emission tomography (FDG-PET), single photon emission computer tomography (SPECT), scalp electroencephalogram (EEG), and intraoperative EEG results [2,5,[7][8][9][11][12][13][14][15][16][17][18][19][20][21][22][23]. However, further investigation is required due to the shortage of cases and the inconsistent and occasionally contradictory findings.…”

High density EEG—What do we have to lose?

“…Multiple studies have demonstrated the utility of electrical source imaging (ESI) of high density EEG recordings for improved localization of epileptic foci in surgical candidates compared to visual interpretation of the conventional scalp EEG (Lantz et al, 2003; Holmes et al, 2008, 2010; Yamazaki et al, 2013; Storti et al, 2013; Mégevand et al, 2014; Michel et al., 2004a,b; Brodbeck et al, 2010; Zumsteg et al, 2005; Lantz et al, 2001; Brodbeck et al, 2009). A large prospective study in 151 pediatric and adult epilepsy surgery patients found that ESI using 126–256 channels and individual brain MRIs as the head model yielded a sensitivity of 84% and a specificity of 88% in identifying the seizure onset zone, which was significantly better than that obtained using low-density EEG recordings, structural MRI, PET exam, or ictal SPECT exams (Brodbeck et al, 2011).…”

EEG–fMRI validation studies in comparison with icEEG: A review

“…Similarly in EEG, an EEG/ESI (EEG source imaging) study on a group of 14 patients (with refractory focal epilepsy and Engel class 1 surgical outcomes) showed that ESI accuracy (indexed by the distance from the nearest surgical margin to the location of a single fit inverse model) improved by around 2 cm from a 31 to a 63 electrode setup, with little change from a 63 to a 123 electrode set-up (Lantz et al, 2003). The diagnostic yield of EEG/ESI increased with highresolution (128-or 256-channel) EEG/ESI and the localization accuracy is 74%-90% for lesional and non-lesional epilepsy Brodbeck et al, 2010).…”