A 31-year-old right-handed woman with implantation of a VNS 3 years prior to her MEG recording presented for further evaluation. Since age 5 years old the patient had focal seizures that began with a “funny feeling,” flushing, and head turning to the right. Some seizures terminated at this point, while at other times her seizures progressed to impair awareness and/or evolved into a bilateral convulsive seizure. Treatment with acetazolamide, carbamazepine, valproic acid, and levetiracetam failed to improve the woman’s seizure frequency. An MRI did not demonstrate any structural brain abnormalities. An epilepsy monitoring unit (EMU) evaluation captured seizures with a broad, right hemispheric onset. An initial MEG recording prior to VNS implantation captured epileptiform activity, which was originally and unsuccessfully analyzed using ECD modeling. The interpretation at the time was that the MEG study did not provide localizing information.\nSynthetic aperture magnetometry (g2) was used to analyze a second MEG recording after the VNS implantation, as well as the previous recording performed prior to VNS implantation. Even though the second recording was separated from the first by 6 years and the raw MEG sensor data were strongly contaminated by artifact from the VNS during the second recording, an equivalent right frontal focus was identified on both recordings (Figure A). This indicates that SAM can reproducibly localize interictal epileptiform activity despite the presence of large artifacts due to the VNS implant. Examination of the source signal series reconstructed from the focus demonstrated MEG discharges that correlated with the simultaneously recorded scalp EEG during the second recording (Figure C), and, importantly, that lacked the high-amplitude fluctuations present in the raw MEG data that were induced by the VNS (Figure B). (For comparison, the raw MEG sensor data prior to VNS implantation are depicted in the top part of Figure B.) Furthermore, during the patient’s second MEG recording an electrographic seizure was recorded by EEG, with a preceding MEG-recorded discharge detected in the source signal series (Figure D). The SNR for the virtual electrodes was at least 50:1.\nGiven the new localizing information provided by the MEG recordings, the patient was determined to be a candidate for invasive monitoring and possible resection. A subdural grid was placed over the right frontal lobe, covering the focus identified on MEG (Figure F). Seizures captured during the invasive monitoring demonstrated electrographic onset (Figure E) very close to the focus of peak kurtosis identified by SAM(g2) on the MEG recordings (Figure F). Following resection, which included the focus identified by SAM(g2), the patient experienced a significant improvement in her seizures, improving from four to six focal seizures with loss of awareness and sometimes evolution to bilateral convulsive seizures monthly to two to four focal seizures with retained awareness monthly. Her scalp EEG recordings demonstrated a greatly reduced frequency of interictal epileptiform activity.
A 31-year-old woman with a VNS implantation three years prior to her MEG recording presented for further evaluation. Since age 5, the patient had focal seizures that began with a “funny feeling,” flushing, and head turning to the right. Some seizures terminated at this point, while at other times her seizures progressed to impair awareness and/or evolved into a bilateral convulsive seizure. Treatment with several antiseizure medicines failed to improve the woman’s seizure frequency. An MRI did not demonstrate any structural brain abnormalities. An EMU evaluation captured seizures with a broad, right hemispheric onset. An initial MEG recording prior to VNS implantation captured epileptiform activity, which was originally and unsuccessfully analyzed using equivalent current dipole modeling (A). The interpretation at the time was that the MEG study did not provide localizing information. As the patient’s seizure focus was not localized with any modality, she received a VNS.\nHowever, the patient continued to have seizures after the VNS implantation. Because we had subsequently implemented SAM(g2) as an alternative to dipole analyses, the patient returned for a second MEG scan. SAM(g2) was used to analyze this second MEG recording, as well as the previous recording performed prior to VNS implantation. Even though the second recording was separated from the first by six years and the raw MEG sensor data were strongly contaminated by artifact from the VNS during the second recording, an equivalent right frontal focus was identified on both recordings (A), a focus not revealed by dipole analysis previously. This indicates that SAM can reproducibly localize interictal epileptiform activity despite the presence of large artifacts due to the VNS implant. (The dipole localization in the presence of VNS artifact is shown in B for comparison. The dipole tails have been omitted for clarity.) Examination of the virtual electrodes reconstructed from the SAM(g2) focus demonstrated MEG epileptiform discharges that correlated with the simultaneously recorded scalp EEG during the second recording (C), and, importantly, that lacked the high-amplitude fluctuations present in the raw MEG data that were induced by the VNS (B). (For comparison, the raw MEG sensor data prior to VNS implantation are depicted in the top part of B.) Furthermore, during the patient’s second MEG recording an electrographic seizure was recorded on EEG, with a preceding MEG-recorded discharge detected in the virtual electrode (D). Given the new localizing information provided by the MEG recordings, the patient was determined to be a candidate for ICEEG and possible resection. A subdural grid was placed over the right frontal lobe, covering the focus identified on MEG (F). Seizures captured during the invasive monitoring demonstrated electrographic onset (E) very close to the focus of peak kurtosis identified by SAM(g2) on the MEG recordings (F). Following resection, which included the focus identified by SAM(g2), the patient experienced a significant improvement in her seizures, improving from four to six focal seizures with loss of awareness and sometimes evolution to bilateral convulsive seizures monthly to two to four focal seizures with retained awareness monthly. Her scalp EEG recordings demonstrated a greatly reduced frequency of interictal epileptiform activity.