PMC8050858_01
(A) Scalp EEG recording of the patient's typical electrographic seizure, showing sharply contoured theta activity in the anterior left temporal head region (T1). (B) Representation of the patient's typical electrographic seizure captured by stereo EEG. Phase 1 consists of fast (20 Hz) activity in the deep contacts of 1MTP (top three waveforms, see black arrow). The patient was asymptomatic throughout phase 1 evaluation. Phase 2 monitoring of seizure onset began with the simultaneous onset of 4-8 Hz evolving spikes in the temporal pole, amygdala and hippocampus, clinically accompanied by unresponsiveness and bilateral stiffening of the arms and hands.
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Some seizures were better localizing, with sharply contoured theta activity in the left temporal head region (Fig. 1A). Nine spontaneous seizures were recorded on sEEG with no involvement of the mesial temporal structures (Fig. 1B).
(A) Sagittal view of the left temporal pole encephalocele (red arrows) as demonstrated by pre-operative MRI. (B) Sagittal view of anatomical position of the sEEG electrodes. (C) Pre-operative coronal-oblique reformatted CT image demonstrating the spatial relationship between the vidian canal (red arrow), foramen rotundum (yellow arrow), and temporal pole encephalocele (green circle). (D) Intra-operative extradural exposure showing defects in the sphenoid bone and encephalocele observed during resection. (E) Uncovered V2 segment of trigeminal nerve passing through foramen rotundum in extradural subtemporal exposure. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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MRI brain showed mild gliosis and ex vacuo dilation of the left greater than right temporal horn. MRI brain was repeated during his phase one evaluation and showed a small left anterior temporal encephalocele with subtle cortical protrusion into the posterior aspect of the left sphenotemporal buttress (Fig. 2A). Nine depth electrodes were implanted in the left temporal lobe to determine whether mesial-temporal structures were part of his seizure onset zone (Fig. 2B). After some thought, the team explained that the most likely cause of his pain was unintentional stimulation of the trigeminal nerve, which lies just inferior to the encephalocele (Fig. 2C). Intraoperatively, the V2 segment of the trigeminal nerve was visualized passing through the foramen rotundum adjacent to the encephalocele (Fig. 2D and E).