A 37-year-old man with a VNS presented for further evaluation. The patient had focal seizures with impaired awareness and occasionally evolution to bilateral convulsive seizures since he was 18 years old. Several events were captured during an EMU admission, all of which localized to the right temporal region. An MRI of his brain did not reveal any structural abnormalities. Single-photon emission computed tomography (SPECT) (Figure F) and PET imaging (Figure G) suggested that a right temporal seizure focus. An MEG recording analyzed by SAM(g2) revealed a right mesial temporal focus centered on the hippocampus (Figure B) and amygdala (Figure C), with some occasional right ventral frontal, right posterior, and lateral temporal spread from this zone, and some additional spread to right insula. [While MEG is less sensitive to deep sources, others have successfully imaged hippocampus and amygdala (–), and given the invasive monitoring results and resection outcome listed below, the hippocampal and amygdalar sources seem reasonable.] While the raw MEG sensor data exhibited artifacts due the VNS, the source signal reconstructions from hippocampus and amygdala (Figure A) displayed no evidence of VNS artifact, with an SNR of 35:1 for the interictal spikes. While clear spikes existed in the source signal data, the EEG data only occasionally exhibited simultaneous interictal spikes.\nInvasive monitoring was planned on the basis of the concordant findings between MEG, SPECT, and PET. Subdural grids were placed over the lateral and mesial aspects of the right temporal lobe, and depth electrodes were inserted into the right amygdala and right anterior and posterior hippocampus. Frequent interictal spikes were seen on the hippocampal and amygdalar electrode contacts (Figure D), and several seizures arose from the anterior hippocampal and amygdalar electrodes, an example of which can be seen in Figure E.\nFollowing the invasive monitoring the patient received a right anterior temporal lobectomy with amygdalohippocampectomy. Prior to his surgery, the patient experienced ~2 seizures per month. Following surgery, the patient was seizure-free for several months, but experienced a breakthrough of two seizures following a reduction in lacosamide dosage, and another breakthrough of four seizures coincident with the onset of an illness.
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.