Intracranial EEG Biomarkers for Seizure Lateralization in Rapidly-Bisynchronous Epilepsy After Laser Corpus Callosotomy.

Simon Khuvis,Sean T Hwang,Ashesh D Mehta

doi:10.3389/fneur.2021.696492

Abstract

Objective: It has been asserted that high-frequency analysis of intracranial EEG (iEEG) data may yield information useful in localizing epileptogenic foci.Methods: We tested whether proposed biomarkers could predict lateralization based on iEEG data collected prior to corpus callosotomy (CC) in three patients with bisynchronous epilepsy, whose seizures lateralized definitively post-CC. Lateralization data derived from algorithmically-computed ictal phase-locked high gamma (PLHG), high gamma amplitude (HGA), and low-frequency (filtered) line length (LFLL), as well as interictal high-frequency oscillation (HFO) and interictal epileptiform discharge (IED) rate metrics were compared against ground-truth lateralization from post-CC ictal iEEG.Results: Pre-CC unilateral IEDs were more frequent on the more-pathologic side in all subjects. HFO rate predicted lateralization in one subject, but was sensitive to detection threshold. On pre-CC data, no ictal metric showed better predictive power than any other. All post-corpus callosotomy seizures lateralized to the pathological hemisphere using PLHG, HGA, and LFLL metrics.Conclusions: While quantitative metrics of IED rate and ictal HGA, PHLG, and LFLL all accurately lateralize based on post-CC iEEG, only IED rate consistently did so based on pre-CC data.Significance: Quantitative analysis of IEDs may be useful in lateralizing seizure pathology. More work is needed to develop reliable techniques for high-frequency iEEG analysis.

Highlights

It is increasingly recognized that a failure of visual inspection to reveal subtle features in intracranial EEG recordings may underlie ambiguity in localizing the epileptogenic zone in surgical epilepsy patients
We retrospectively examined the pre-operative intracranial EEG (iEEG) in three subjects with seizures exhibiting very rapid bisynchrony, in whom seizures lateralized after corpus callosotomy (CC) [as in previous reports [28,29,30]] in order to attempt to identify the hemisphere containing the epileptogenic zone
Fitting a general linear model showed a significant effect of pathology laterality on the fraction of high-high frequency oscillations (HFOs) channels in 1/3 subjects in the preCC intervals

Summary

Introduction

It is increasingly recognized that a failure of visual inspection to reveal subtle features in intracranial EEG (iEEG) recordings may underlie ambiguity in localizing the epileptogenic zone in surgical epilepsy patients. Interictal epileptiform discharges (IEDs) have long been recognized as biomarkers of epileptogenicity [11,12,13,14], with the region of brain producing IEDs described as the irritative zone (IZ) [15]. Resection of regions producing HFOs >250 Hz correlated with better surgical outcomes than zones producing IEDs [4, 21], a 2014 Cochrane Review concluded that there was insufficient evidence at this time to use HFOs in surgical planning [22], and several recent studies have challenged the reported special utility of HFOs in defining the epileptogenic zone in individual patients [23, 24]

Methods

Results

Discussion

Conclusion