Magnetoencephalography in fronto-parietal opercular epilepsy

Objective: To clarify the clinical and neurophysiological profiles of fronto-parietal opercular epilepsy in which epileptic spikes are detected with magnetoencephalography (MEG) but not with scalp electroencephalography (EEG). Methods: Four patients presented with epileptic spikes localized to the fronto-parietal opercular cortex, which were only appreciated following MEG recordings. Results: In all cases, seizure semiology suggested early activation of the operculum and lower peri-rolandic cortex consistent with the somatotopic organization of this region, i.e. tingling sensation involving the throat and hemi-face or contralateral upper limb, and spasms of the neck and throat. MEG spikes were localized in the fronto-parietal operculum. Three of the four patients underwent invasive electrocorticography and/or stereo-EEG recordings, and spikes were confirmed to arise from the estimated area of MEG dipole localization. Two patients remained seizure-free for over 1 year after resection of the epileptogenic region; the other patient declined resective surgery due to proximity to the language cortex. Conclusion: This study demonstrates the usefulness of MEG in localizing spikes arising from within the fronto-parietal opercular regions, and implies that MEG may provide localizing information in patients with symptoms suggestive of opercular epilepsy, even if scalp EEG recordings fail to disclose any epileptogenic activities.