A 6-year-old girl with a VNS implantation for pharmaco-resistant seizures presented from an outside institution for further evaluation. The patient was known to have a cortical dysplasia. The patient’s EEG revealed numerous distributed spikes, suggesting that the presence of multiple foci. Beamforming of the MEG recording with SAM(g2) revealed bilateral orbitofrontal activity with a much more kurtotic signal on the left than the right. SAM(g2) also identified bilateral temporal activation with a much greater involvement of the right hemisphere. There was an additional focus of lesser kurtosis encompassing the left insula and spreading to the left occipitoparietal cortex. The source signal reconstructions corresponding to these foci possessed an SNR of about 35:1 and exhibited numerous interictal spikes with simultaneous EEG spikes.
A 36-year-old right-handed woman with implantation of a VNS 6 years prior to her MEG recording presented for further evaluation. The patient had focal seizures with a sensory aura and impaired awareness following a childhood head injury. Her seizures were pharmaco-resistant, and evaluation with scalp EEG suggested that a left temporal focus. EMU evaluation 1 month prior to her MEG scan captured episodes of generalized spike-wave discharges. An MRI of her brain did not demonstrate any structural abnormalities. The woman’s MEG recording, beamformed with SAM(g2), revealed foci in the left dorsal frontal cortex, bilateral anterior insula, right prefrontal cortex, and left occipital cortex. The VNS artifact was absent from the source signal reconstructions for these areas, and all interictal spikes had an SNR of at least 35:1. The spikes present in the source signal series corresponded with spikes in the accompanying EEG, though the EEG spikes had a broad, left hemispheric field.