Ictal EEG source imaging and connectivity to localize the seizure onset zone in extratemporal lobe epilepsy

Abstract

To evaluate the yield of Functional Connectivity (FC) in addition to low-density ictal Electrical Source Imaging (ESI) in extratemporal lobe epilepsy (ETLE), using an automated algorithm for analysis. Method: Long-term EEG monitoring of consecutive ETLE patients who underwent surgery was reviewed by epileptologists, and seizure onsets characterized by rhythmical activity were identified. A spectrogram-based algorithm was developed to select objectively the parameters of ESI analysis. Two methods for SOZ localization were compared: i) ESI power, based on LORETA exclusively; ii) ESI + FC, including a Granger causality-based connectivity analysis. Results were determined at a sublobar level. The resection zone, in relation to 1-year follow-up surgical outcome, was considered as reference standard for diagnostic accuracy analyses. Results: Ninety-four seizures from 24 patients were analyzed. At seizure-level, ESI power showed 36 % sensitivity and 72 % specificity (accuracy: 45 %). ESI + FC significantly improved the accuracy, with 52 % sensitivity and 84 % specificity (accuracy: 61 %, p = 0.04). Results of ESI + FC were equally valuable in patients with lateralized or bilateral/generalized visual interpretation of ictal EEG. In a patient level sub-analysis, upon blinded clinical interpretation, ESI + FC showed a correct localization in 67 % of patients and substantial interrater agreement (kappa = 0.64), against 27 % achieved by ESI power, with fair inter-rater agreement (kappa = 0.37). Conclusion: FC significantly improves SOZ localization compared to ESI solely in ETLE. Ictal ESI + FC could represent a novel option in the armamentarium of presurgical evaluation, aiding also in patients with visually non-localizable scalp ictal EEG. Prospective studies evaluating the clinical added value of automated low-density ictal ESI may be justified.

Source imaging of seizure onset predicts surgical outcome in pediatric epilepsy

“…ESI still presents technical challenges that may hamper clinical implementation as many epilepsy centers lack the necessary expertise to perform pre- and post-processing of ictal data. Fully automated source imaging methods may potentially minimize these technical obstacles ( Baroumand et al, 2018 ; Koren et al, 2018 ; Vespa et al, 2020 ).…”

Functional Near-Infrared Spectroscopy and Its Clinical Application in the Field of Neuroscience: Advances and Future Directions

“…Third, compared with EEG, the temporal resolution of fNIRS may be suboptimal to capture individual neurologic events. Seizures spread quickly between neurons on a millisecond timescale and can require a high sampling rate for accurate source localization (Coelli et al, 2019;Vespa et al, 2020). Sampling rates of clinical EEG are typically between 256 to 1024 Hz, whereas the sampling rate of fNIRS is an order of magnitude lower.…”

Improving surgical outcome with electric source imaging and high field magnetic resonance imaging

“…Pooled data sensitivity for ictal ESI was 89.9 % (95 % CI: 81.8-94.6 %), significantly higher than interictal ESI, and specificity was 46.9 % (95 % CI: 30.5-63.9 %) [113]. Other studies published after this systematic review also report a high concordance between ictal ESI and the brain area considered to compose the EZ by means of postoperative results [114,[116][117][118][119][128][129][130]. Patients with complex patterns of IED appear to benefit most critically from the addition of ictal ESI [118,119].…”

“…Spatio-temporal decomposition methods have been incorporated into ESI techniques, permitting source imaging of oscillatory activity, in addition to the classic analysis of static voltage maps [111]. These innovations resulted in recent applications of ESI to localize abnormal non-epileptiform activity, as focal slowing [112], and, importantly, to localize ictal activity [113][114][115][116][117][118][119].…”