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From palliative care to successful resection: The value of stereoelectroencephalography patterns in two cases of MRI-negative epilepsy within eloquent language areasAuthor Affiliations:
Author:
Dandan Liu1,2,Wuchen Wu1,2, Xianyun Liu1,2, Xin Shi1,2, Mengmeng Fu1,2, Xianghong Meng1,2
¹ Shenzhen University, Shenzhen, China
² Shenzhen University General Hospital, Shenzhen, China
Corresponding author:
1Mengmeng Fu: fumengmeng2019@163.com
2Xianghong Meng: dr_mengxh@163.com
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Abstract
Background
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Surgical management of MRI-negative drug-resistant epilepsy (DRE) in the eloquent language cortex poses a significant challenge. The absence of a clear structural lesion on MRI often leads to palliative rather than curative treatment approaches. This case report highlights the critical role of specific stereoelectroencephalography (SEEG) patterns in guiding successful resective surgery in this high-stakes scenario.Case Presentation:
We present the cases of two patients with MRI-negative DRE localized to Broca's area and Wernicke's area, respectively. Following non-diagnostic non-invasive evaluations, SEEG monitoring was performed. In both cases, the SEEG revealed characteristic interictal patterns highly suggestive of focal cortical dysplasia type II (FCD II), including continuous rhythmic spiking and sleep-wake cycle modifications. Based on these definitive electrophysiological findings, the patients underwent awake resection with intraoperative monitoring. Histopathological examination confirmed FCD Type II in both instances.
Conclusion
These cases demonstrate that a distinct SEEG signature can reliably indicate an underlying FCD II, even in MRI-negative epilepsy involving critical language areas. This finding can empower clinicians to pursue potentially curative resective surgery with an excellent prospect of seizure freedom and functional preservation. The identification of these SEEG characteristics is, therefore, pivotal in the surgical decision-making algorithm for similar complex cases.
Keywords:
Focal cortical dysplasia type II
Stereotactic electroencephalography (SEEG)
MRI-negative epilepsy
Language area
Surgical decision-making
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Background
Surgical resection is the preferred treatment option for drug-resistant epilepsy caused by focal Cortical Dysplasia (FCD) [1]. For well-circumscribed Type II FCD, complete resection of the lesion carries a high probability of achieving seizure freedom [2, 3], with literature reporting postoperative Engel Class I rates reaching 83% [4]. However, surgical outcomes are far less satisfactory for FCD located in eloquent areas, particularly in patients with MRI-negative findings [1]. The primary reasons include incomplete resection of the lesion, inability to resect due to overlap with functional cortex, or reluctance to proceed with resection because of unclear anatomo-functional relationships.
For such patients, clinical management often turns to palliative treatments such as neuromodulation therapy or stereotactic electroencephalogram (SEEG)-guided thermocoagulation. However, the therapeutic outcomes are suboptimal: the seizure-free rate after thermocoagulation for FCD is only 18% [5], while the seizure-free rate following Vagus Nerve Stimulation surgery is less than 10% [6]. Therefore, finding opportunities for curative surgery for this patient population represents a significant clinical challenge.
This paper reports two cases of MRI-negative drug-resistant epilepsy from our center, where the epileptogenic zones were adjacent to or overlapped with language areas. SEEG monitoring in both cases revealed characteristic interictal discharge patterns typical of Type II FCD, and successful surgical resection of the epileptogenic focus was ultimately performed.
Case Presentation
1. Clinical Data
A retrospective analysis was conducted on two patients with drug-resistant epilepsy who underwent surgical resection at the Department of Neurosurgery, Shenzhen University General Hospital between October 2022 and July 2024. Inclusion criteria were: 1) no definitive lesion on preoperative 3T MRI; 2) SEEG-confirmed epileptogenic zone adjacent to or overlapping with eloquent language cortex; 3) definitive postoperative histopathology. All patients completed a comprehensive presurgical evaluation, including long-term video-electroencephalogram(VEEG) monitoring, 3T brain MRI, Fluorodeoxyglucose-Positron Emission Tomography-Computed Tomography (FDG-PET-CT), neuropsychological assessment, and language lateralization (Wada test or functional Magnetic Resonance Imaging).
2. Case 1
A 26-year-old right-handed female had a 10-year history of drug-resistant epilepsy. Her seizure semiology typically began with an aura of palpitations, followed by speech arrest and perioral paresthesia. This was accompanied by oral automatisms (such as covering her mouth with either hand), which subsequently evolved into perioral dystonia, salivation, jaw clonus, and occasionally secondary generalized tonic-clonic seizures. Her seizure frequency was high, exceeding 10 episodes per month.
Preoperative evaluation included scalp EEG, which showed no interictal epileptiform discharges and revealed an unclear ictal onset. Neuroimaging with 3T MRI and PET-CT was non-lesional. The core ictal discharge site of SEEG was localized to Broca’s area(Fig. 1A). Language lateralization was established via the Wada test, which confirmed left-hemisphere language dominance.
3. Case 2
A 29-year-old right-handed female had a 10-year history of drug-resistant epilepsy. Her seizures were characterized by an initial aura of palpitations and fear, followed by progressive speech and motor impairment. Specifically, she experienced an inability to type or speak despite preserved auditory comprehension, subsequently progressing to right facial twitching, right arm elevation, and version of the head and eyes to the right, with frequent secondary generalization. Seizure frequency was relatively low, occurring 1–2 times per month.
Preoperative evaluation included scalp electroencephalogram(EEG), which demonstrated frequent interictal epileptiform discharges over the left fronto-temporal region, with ictal onset originating from the left hemisphere. Structural MRI (3T) was non-lesional, while PET-CT revealed focal hypometabolism in the left parietal lobe. The core ictal discharge site of SEEG was localized to Wernicke’s area(Fig. 1B). Functional MRI supported left-hemisphere language dominance.
Fig. 1
Arrow: Core electrode (A,B)
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4.Management and Outcome4.1 SEEG Evaluation and Findings
Due to inconclusive non-invasive evaluations, SEEG implantation was performed to delineate the epileptogenic zone. SEEG analysis was conducted independently by two senior epileptologists, with final interpretation requiring consensus. Characteristic interictal patterns highly suggestive of FCD II were recorded in both cases(Fig. 2) including:
Near-continuous Epileptiform Discharges.
Repetitive Rhythmic Spikes/Sharp Waves.
Sleep-Wake Cycle Modification: Discharge patterns differed between wakefulness and sleep. During wakefulness, discharges were more localized. During sleep, the discharge field often expanded, and spikes frequently transformed into polyspikes or delta brushes .The interictal discharge interval during the sleep period was longer than that during the awake period.
Ictal Onset: The ictal onset zone was concordant with the area of maximal interictal abnormalities, often exhibiting an initial phase of repetitive fast spike bursts followed by low-voltage fast activity.
Fig. 2
SEEG Characteristics
Awake-state discharges: persistent rhythmic sharp/spike-slow waves(A,B) .Sleep-state discharges: polyspike-slow waves and delta brushes(C,D).Ictal onset site matched the location of interictal discharges, and the ictal onset was characterized by repetitive fast spike bursts, followed by low-voltage fast activity(E,F).
4.2 Surgical Treatment and Postoperative Outcome
Despite the core SEEG discharge zone being located within the presumed language functional area, based on the characteristic FCD type II patterns and the "functional shift" theory, the decision was ultimately made to perform resection of the epileptogenic focus under awake anesthesia after comprehensive evaluation (Fig. 3). Intraoperative direct electrical stimulation (DES) was utilized for language area mapping, and resection boundaries were guided by electrocorticography (ECoG) monitoring. Postoperative pathological examination confirmed FCD type IIa in both cases. At the final follow-up (Case 1: 36 months; Case 2: 24 months), both patients achieved seizure-free status (Engel Class Ia) without new language dysfunction or neurological deficits.
Fig. 3
Red circle: Resection site
Conclusion and Discussion
Our findings demonstrate that specific SEEG features can reliably suggest a histopathological diagnosis of FCD II, even in the absence of an MRI lesion. This electrophysiological signature empowered us to offer potentially curative resective surgery to two patients with epilepsy originating from language areas, who would otherwise be considered poor candidates for resection.
Arious terms have been used in previous literature to describe the EEG discharge patterns of focal cortical dysplasia (FCD), including "continuous epileptiform discharges," "frequent epileptiform discharges superimposed on irregular slow waves," "ictal‑like bursting discharges," and "brushing patterns"[7–10]. A recent study by Radek Janca et al. further quantified the discharge characteristics of different FCD types, revealing that the inter-discharge intervals in FCD type II were significantly shorter than those in type I (type II: mean 0.60 s, range 0.49–0.65; type I: mean 0.77 s, range 0.65–0.86), with discharges also lasting notably longer in type II (mean 2.6 min, range 0.7–4.6) compared to type I (mean 0.6 min, range 0.4–1.6) [11]. Moreover, FCD type II exhibited distinct discharge patterns between wakefulness and sleep: higher discharge frequency during wakefulness and frequent transformation of spikes into polyspikes during sleep [11]. A critical factor in our decision-making was the well-documented phenomenon of functional reorganization or "functional shift" in FCD II. The dysplastic cortex itself often lacks normal function, which may have been redistributed to adjacent perilesional cortex[12]. This theoretical framework, combined with intraoperative confirmation via DECS that the planned resection cavity margins were not essential for language, allowed for safe resection.
The limitations of SEEG, such as its limited spatial sampling between electrodes, underscore the importance of intraoperative ECoG to refine resection boundaries and ensure completeness. Furthermore, these characteristic patterns might not be detectable on scalp EEG, especially for deep-seated or small FCDs, highlighting the indispensability of intracranial monitoring in such cases.
In conclusion, for carefully selected patients with MRI-negative epilepsy in language areas, the identification of SEEG features highly suggestive of FCD II can be a pivotal factor in guiding the decision towards resective surgery. This strategy can lead to excellent seizure outcomes without permanent neurological morbidity, provided it is executed within a rigorous framework of multimodal evaluation, including intraoperative awake mapping and monitoring.
Abbreviations
DRE
Drug-resistant epilepsy
SEEG
Stereoelectroencephalography
FCD
Focal cortical dysplasia
FDG-PET-CT
Fluorodeoxyglucose-Positron Emission Tomography-Computed Tomography
DES
Intraoperative direct electrical stimulation
ECoG
Electrocorticography
EEG
Electroencephalogram
Declarations
Ethics statement
The studies involving humans were approved by the Medical Research Ethics Review Committee, Shenzhen University General Hospital.
Consent for publication
Written informed consent was obtained from the patient for publication of this case report and any accompanying images.
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Data Availability
No datasets were generated or analysed during the current study.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest.
Competing interests
The authors declare no competing interests.
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Funding
This study was supported by the Stable Support Project of Shenzhen (Project NO.20231122135121001)
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Author Contribution
D.D.L: Conceptualization, Investigation, Methodology, Writing–original draft, Writing–review & editing. W.C.W: Supervision, Validation. XYL: Supervision, Validation. X.S: Supervision & Validation. M.M.F: Funding acquisition, Resources, Writing–review & editing. X.H.M: Funding acquisition, Resources, Writing–review & editing.
Acknowledgements
We would like to express our sincere gratitude to our patient and his family for their cooperation in the preparation of this report.
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