PMC9674497_01
Timeline and prior SEEG. A. Timeline showing the prior epilepsy evaluation and treatment in addition to the management at our institution. B. MEG (sagittal view) showing left frontal interictal activity. C. Schematic showing the prior SEEG primarily targeting the left frontal region which was completed at an outside institution. D. SPECT result from the epilepsy monitoring unit at our institution showing multiple areas of hyperperfusion, including in the left frontal region.
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A 50-year-old left-handed man presented to the epilepsy clinic for evaluation of longstanding drug-resistant focal epilepsy (Fig. 1A). He had undergone extensive evaluations at outside institutions (Fig. 1), including magnetoencephalography (Fig. 1B), a Wada test which showed left language dominance, and stereo-EEG (SEEG) monitoring targeting the left frontal region 2 years prior (Fig. 1C) which recorded numerous seizures of left frontal onset (in the mesial portion of the left superior frontal gyrus; contacts LM2-4, and LS 1-2). Subtraction ictal single-photon emission computed tomography (SPECT) coregistered to MRI (SISCOM) performed during a clinical seizure showed multiple small nonspecific areas of hyperperfusion including the left medial frontal region (Fig. 1D).
RNS data. A. CT showing the configuration of the previously placed RNS leads. Initially the left frontal depth (LDMF) and the lateral frontal cortical strip (LFO) were placed. However, due to lack of efficacy, LFO was disconnected and a strip over the supplementary motor area (SMA) was placed. There was an attempt at lead removal, but due to adhesions, this was not possible. B. RNS EEG data showing presumed seizure activity (or robust interictal activity) in the LDMF leads, consisting of a spike-wave complex followed by a high frequency discharge. C. Simultaneously acquired RNS ECoG (top) and scalp EEG (longitudinal bipolar montage) from EMU admission (bottom). Seizure onset in RNS occurs in LDMF electrode and precedes scalp onset by around 1 s. Ictal activity resembles that observed at other times in the RNS data (as in panel B).
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Due to concerns related to disruption of language function and insufficient seizure onset localization, a resection was not performed and a responsive neurostimulator (RNS) was implanted to target the area of presumed SOZ including a left frontal depth electrode and two cortical strip electrodes targeting the lateral frontal cortex and the supplementary motor area (SMA) (Fig. 2A and 2B). Sixteen seizures with the typical semiology of grimacing followed by suddenly falling in one direction, curling into the fetal position, and making high-pitched vocalizations were captured with onset maximal over the left frontocentral region (Fig. 2C).
SEEG implantation and ictal SEEG pattern. A. Schematic of the SEEG plan at our institution. The target of each electrode is seen in the table next to the figure showing the relationship of SEEG trajectories to the MEG, SPECT, and prior SEEG results. The image demonstrates that there was much denser left frontal coverage with the second SEEG targeting the supplementary motor area than with the first SEEG. An axial view of the schematic of SEEG implantation is also shown. With the axial view, the region highlighted in orange shows the area of the SPECT abnormality and green the area of the MEG cluster. The SEEG leads highlighted in red were associated with seizure onset and those in orange with early seizure spread. The leads in black display the location of the RNS. B.SEEG from the second implantation in bipolar montage showing a typical seizure, with many leads omitted to focus on the most active leads. C. Brain schematic comparing the presumed seizure onset from the first SEEG (green dots) to the seizure onset determined by the SEEG at our institution (red dots). D. SEEG from the first implantation done at an outside institution showing the similar pattern of ictal onset. SEEG parameters: low frequency filter: 1 Hz, high frequency filter: 70 Hz, notch: 60 Hz, sensitivity: 10 uV/mm, time base: 30 mm/sec. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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One year following initial presentation, the patient underwent repeat SEEG evaluation (Fig. 3A). A combination of the prior work-up, including magnetoencephalography (showing left frontal interictal activity) and previous SEEG, in addition to the recent scalp EEG and SISCOM was used to plan repeat invasive monitoring with denser coverage over the left frontal region than the initial SEEG (Fig. 3A). On SEEG, onset involved polyspikes primarily at contacts within in the superior frontal gyrus in the pre-SMA and SMA region including LE 6-8, LP 12-17, and LV 12-17 with early involvement of LEN 9-10, LN 8-9, LY 14-15, LF 4-5 and 9-10 (Fig. 3B). The ictal pattern was similar to what was seen on the first SEEG (Fig. 3D).
Outcome information. A. Post-operative MRI showing expected postoperative changes from left frontal lobe corticectomy (arrow). In addition, a brain schematic shows the area of seizure onset determined by SEEG in relationship to the area of resection (green). B. Difference in seizure frequency and severity, quality of life and sleep from prior to and after surgery. C. Results of both presurgical and postsurgical neuropsychological testing showing mild differences in postsurgical testing compared to presurgical testing, with slightly more difficulty with verbal learning and memory and decline in semantic fluency. However, there was also mild improvement on measures of naming, lexical fluency, and executive function. Abbreviations: BNT = Boston Naming Test; BVMT-R = Brief Visuospatial Memory Test - Revised; DKEFS = Delis-Kaplan; Executive Function System; HVLT-R = Hopkins Verbal Learning Test - Revised; N/a = not applicable; TMT B = Trail Making Test Part B; WAIS-IV FSIQ = Wechsler Adult Intelligence Scale 4th Edition, Full Scale IQ; WCST = Wisconsin Card Sorting Test. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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The patient subsequently underwent an awake focal cortical resection of the SOZ (Fig. 4A) with language and motor mapping using the tablet-based cognitive testing platform know as the "NeuroMapper" developed by David Sabsevitz, Ph.D.; Mayo Clinic, Jacksonville, FL and Medical College of Wisconsin). Post-operative neuropsychological testing showed mild differences compared to the pre-operative testing (Fig. 4C). The patient has remained seizure free (Engel IA/ILAE Class 1 outcome) throughout last follow-up (8 months after surgery) and showed subjective improvements related to seizure severity, quality of life, and sleep (Fig. 4B).