Abstract
Non-invasive studies to predict regions of seizure onset are important for planning intracranial grid locations for invasive cortical recordings prior to resective surgery for patients with medically intractable epilepsy. The neurosurgeon needs to know both the seizure onset zone (SOZ) and the region of immediate cortical spread to determine the epileptogenic zone to be resected. The immediate zone of spread may be immediately adjacent, on a nearby gyrus, in a different lobe, and sometimes even in the contralateral cerebral hemisphere. We reviewed consecutive simultaneous EEG/MEG recordings on 162 children with medically intractable epilepsy. We analyzed the MEG signals in the bandwidth 20–70 Hz with a beamformer algorithm, synthetic aperture magnetometry, at a 2.5 mm voxel spacing throughout the brain (virtual sensor locations, VSLs) with the kurtosis statistic (g2) to determine presence of excess kurtosis (γ2) consistent with intermittent increased high frequency spikiness of the background. The MEG time series was reconstructed (virtual sensor signals) at each of these VSLs. The VS signals were further examined with a relative peak amplitude spike detection algorithm. The time of VS spike detection was compared to the simultaneous EEG and MEG sensor signals for presence of conventional epileptiform spike morphology in the latter signals. The time of VS spike detection was compared across VSLs to determine earliest and last VSL to show a VS spike. Seven subjects showed delay in activation across VS locations detectable on visual examination. We compared the VS locations that showed earliest and later VS spikes with the locations on intracranial grid locations by electrocorticography (ECoG) that showed spikes and both onset and spread of seizures. We compared completeness of resection of VS locations to postoperative outcome. The VS locations for spike onset and spread were similar to locations for ictal onset and spread by ECoG.
Highlights
Non-invasive studies to predict regions of seizure onset are important for the planning of intracranial grid locations for epilepsy
SUBJECTS We initially reviewed consecutive simultaneous EEG/MEG recordings between January 2006 and December 2008 for 162 children and adolescents with medically intractable epilepsy who were admitted for non-invasive Phase I presurgical evaluation
All subjects had one or more VS locations identified by the synthetic aperture magnetometry (SAM) + g 2 [SAM(g 2)], evaluation for excess kurtosis
Summary
Non-invasive studies to predict regions of seizure onset are important for the planning of intracranial grid locations for epilepsy. The surgeon needs to know both the seizure onset zone (SOZ) and the region of immediate cortical spread to determine the epileptogenic zone (EZ) to be resected (Engel, 1996; Wiebe et al, 2001; Luders et al, 2006). Prediction of intracerebral locations of sources for recorded extracranial MEG signals requires mathematical source localization algorithms. Source localization algorithms in the beamformer category are spatial filters and have very good signal to noise resolution. The beamformer algorithm, as a spatial filter, can “tune” the MEG sensor array to enhance the signal arising in a specific location while diminishing brain signals arising from other locations
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