PMC6883308_01
A : Surface overlay of the implanted sEEG electrodes showing left hemisphere implant covering anterior orbitofrontal (Ant OF), posterior orbitofrontal (Post OF), lateral frontal (Lat Frontal), amygdala (Amyg), anterior hippocampus (Ant HC), posterior hippocampus (Post HC), basal temporal (Basal MEG), temporal pole (Temp Pole), superior temporal gyrus (STG insula), posterior temporal (Post Temp) and parietal insular (Par Insular) electrode. B : Normal pre-surgical MRI- FLAIR sequence in coronal section. C : Seizure onset pattern recorded from the implanted sEEG electrodes showing electrodecrement response (green thick arrow) at LAH 1-4 and LPH 1-4 electrodes followed by the onset of low amplitude fast activity (green thin arrow) at LAH 1-4 contacts followed by LPH 1-6 followed by LBT 1-3 contacts which then transitions to ictal pattern. D, E : MRI brain (1-year post-explantation) with FLAIR sequence and F, G : with T2 sequence showing the lesions (blue arrows) at the site of prior sEEG electrode trajectory. Left anterior hippocampus (LAH), left posterior hippocampus (LPH), left basal temporal (LBT) and left temporal pole (LTP) are shown.
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In some of the seizures, the ictal EEG change was delayed from the clinical onset by up to 10 s. 3 T MRI of the brain with epilepsy protocol was non-lesional and did not show any hippocampal pathology (Fig. 1B). Considering the non-lesional MRI, delayed EEG onset from the clinical onset, and with the rapid frontal involvement at the ictal onset, the patient underwent sEEG evaluation. sEEG electrodes targeted the left amygdala, hippocampus, temporal pole, orbitofrontal, insular, anterior and mid-cingulate, and posterior temporal regions (Fig. 1A). The seizure onset pattern for one of the seven stereotypical seizures is shown in Fig. 1C. Follow-up MRI at one year (Fig. 1D-G) showed multiple small superficial areas of cortical encephalomalacia and deep white matter lesions in the area of previous sEEG electrode implantation.
PMC6883308_02
A : Pre-surgical MRI brain shown in coronal section, with no pathology. B and C : MRI post-explantation:Coronal GRE sequences showing electrode tract (linear) and superficial (nodular) hemosiderin deposit (red arrows). D : Seizure onset pattern recorded from the implanted sEEG electrodes showing transition from inter ictal to ictal activity (blue arrow) at RF 5-7, RAOF 2-7 and RPOF 7-9 electrodes. E : Left side shows rhythmic delta activity (green arrow : LAF 1-6, LAOF 7-10 and LPOF 8-10) at the same time, but no definitive ictal pattern, showing that the seizure onset lateralizes to the right side. Right frontal (RF) right anterior frontal (RAF), right anterior orbitofrontal (RAOF), right posterior orbitofrontal (RPOF), left anterior frontal (LAF), left anterior orbitofrontal (LAOF) and left posterior orbitofrontal (LPOF) are shown.
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MRI (Fig. 2A) and FDG-PET were normal. MEG was not performed due to the absence of inter-ictal abnormalities. The hyperkinetic motor seizure (Fig. 2D and E) has an evolving pattern in the right frontal leads with simultaneous rhythmic activity in the left frontal leads. OXC 300 mg twice a day. One year post-explantation, an MRI (Fig. 2B and C) showed nodular foci and thin lines of hemosiderin along the electrode tracks.
PMC6883308_03
A : Pre-surgical MRI of the brain shown in coronal section, with no pathology. B and C : Immediate post-explantation CT scan showed a small left parietal extra-axial hemorrhage and edema at the site of implantation (red arrows) in coronal section (B) and axial section (C). D : Seizure onset pattern recorded from the implanted sEEG electrodes showing brief low amplitude fast activity in L STG electrodes (thin blue arrow), which then stopped, followed by the development of a clear ictal pattern in LAHC and LPHC followed by LAMYG (thick blue arrows). Left amygdala (LAMYG), left anterior hippocampus (LAHC), left posterior hippocampus (LPHC) and left superior temporal gyrus (LSTG).
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MRI of the brain was negative (Fig. 3A), and an FDG-PET scan showed decreased uptake in the left temporal and parietal regions. MEG showed left intra-sylvian and basal temporal and temporo-parietal spikes. It was noted that the patient had independent seizure foci in the superior temporal gyrus and the anterior hippocampus (Fig. 3D). Immediate post-explantation CT scan showed a small left frontal extra-axial hemorrhage and edema at the site of implantation, which was clinically silent (Fig. 3B and C).