Radiofrequency thermocoagulation in focal epilepsy: A retrospective cohort study

OBJECTIVE

Stereoelectroencephalography-guided radiofrequency thermocoagulation (SEEG-guided RFTC) has been increasingly used as diagnostic and therapeutic approach for drug-resistant focal epilepsies (DREs). We aimed to describe seizure outcomes of RFTC before and after further neurosurgical intervention.

METHODS

Retrospective single-institution case series of patients who underwent SEEG-RFTC. The primary outcome was Engel class I-IV classification ([responders Engel I-III and non-responders Engel IV]) at last follow-up after RFTC and prior to further neurosurgical intervention (open surgical resection, laser ablation, and neuromodulation).

RESULTS

Twenty-five patients (median age 18.9 years) with DRE were included. The median follow-up time after RFTC was 7.2 months, including 20 patients who underwent further intervention (median follow-up time of 7.3 months) and 5 without intervention (median of 3.5 months). From the patients who had further intervention, 17 (85%) underwent surgical procedure (laser ablation 53%, open surgical resection 47%) (median 4.4 months) and 3 (15%) had responsive neurostimulators placed (median 6.9 months). Prior to further intervention (median follow-up 3.5 months after RFTC), 12 (48%) patients were classified as responders (12% Engel class I, 16% class II, and 20% class III) and 13 (52%) as non-responders. Following neurosurgical intervention, 17 (68%) patients were followed for a median time of 2.7 months and 3 were lost to follow-up. Of eight initial RFTC responders, 87.5% and 12.5% had Engel classes I and III, respectively. Of nine who were non-responders, 33% had Engel class I, 22% II and III, and 44% IV outcomes following further intervention. No neurologic complications were reported.

SIGNIFICANCE

SEEG-guided RFTC is a well-tolerated procedure and a beneficial diagnostic approach prior to further neurosurgical interventions in patients with DRE.

PLAIN LANGUAGE SUMMARY

SEEG-guided RFTC is a well-tolerated procedure and in the patients who experienced initial seizure reduction (n = 8), subsequent neurosurgical intervention (surgery or neuromodulation) led to favorable seizure outcomes (87.5% seizure freedom and 12.5% worthwhile seizure improvement).

The impact of radiofrequency thermocoagulation on brain connectivity in drug-resistant epilepsy: Insights from stereo-electroencephalography and cortico-cortical evoked potentials

OBJECTIVE

To investigate whether local lesions created by stereo-electroencephalography (SEEG)-guided radiofrequency thermocoagulation (RFTC) affect distant brain connectivity and excitability in patients with focal, drug-resistant epilepsy (DRE).

METHODS

Ten patients with focal DRE underwent SEEG implantation and subsequently 1 Hz bipolar repetitive electrical stimulation (RES) for 30 s before and after RFTC. Root mean square (RMS) of cortico-cortical evoked potentials (CCEPs) was calculated for 15 ms to 300 ms post-stimulation with baseline correction. Contact pairs were categorized as both coagulated, hybrid, or both non-coagulated. The data were divided into nine categories based on the stimulating and recording contact pair combinations. RMS of CCEPs was compared before and after (<12 h) RFTC using a two-sample t test (Hochberg corrected, p < 0.05) for each patient. Boost score, indicating power increase during seizures before RFTC relative to baseline, was analyzed in 4 s windows with 1 s overlap during seizure duration.

RESULTS

RFTC altered connectivity across all categories. Of interest, decreases and increases in RMS were observed in connections between non-coagulated contacts distant from coagulation site (range: 1.09-85 mm, median = 17.7 mm, interquartile range [IQR] 10.1-32.3). Contact pairs involved in significantly altered non-coagulated connections showed a higher boost score correlation in the theta, beta, and gamma bands, as well as a stronger maximum correlation with coagulated sites in the delta band than contacts for which connectivity did not change after RFTC.

SIGNIFICANCE

This study highlights how local lesions alter distant brain connectivity, providing insights for future research on epilepsy network changes and seizure outcomes following RFTC.

The prognostic value of cortical stimulation induced seizures using stereo EEG in presurgical evaluation of focal epilepsies

The value of stimulation-induced seizures for multimodal determination of the epileptogenic zone in preoperative epilepsy diagnostics has not yet been sufficiently investigated. Patients with focal pharmacorefractory epilepsy who underwent invasive electroencephalography with cortical 50 Hz stimulation at the Epilepsy Center Erlangen between 2018 and 2023, had at least one stimulation-induced seizure, underwent resective epilepsy surgery, and had a postoperative follow-up ≥ 1 year were analyzed. 20 patients were included, 11 (55.0%) with temporal, 7 (35.0%) with frontal and 2 (10.0%) with parietal lobe epilepsy. 12 patients (60.0%) had a good Engel outcome (Engel 1A). Associated with a good vs. poor (Engel 1B-4) surgical outcome were not only the percentage of resected electrode contacts of the spontaneous seizure onset zone, SOZ (p = 0.005), but also the stimulation SOZ (p = 0.022), as well as stimulation-induced seizure with a typical seizure semiology (p = 0.033), the electrodes inducing a stimulation-induced seizure (p = 0.014), electrodes with an identical seizure onset pattern (p = 0.035), and the occurrence of low voltage fast seizure onset pattern, LVFA (p = 0.015). ROC analyses showed that the AUC for the predictors of the spontaneous SOZ were greatest for the stimulation SOZ (AUC 0.876) and stimulation-induced seizures with LVFA (0.860). Analysis of combined predictors showed higher odds of predicting SOZ for combinations including LVFA. Electroclinical stimulation seizures have prognostic value in determining the epileptogenic zone. Characteristics such as the seizure onset zone, seizure pattern and stimulation seizure semiology predict seizure freedom in case of resection of electrode contacts. Electrodes should be resected where both stimulation seizures have been induced or the seizure pattern has been localized and low voltage fast seizure pattern has occurred.

Whether radiofrequency thermocoagulation guided by stereotactic electroencephalography can benefit drug-resistant epilepsy in the early follow-up stage

BACKGROUND

Stereotactic electroencephalography (SEEG) has emerged as a widely utilized diagnostic approach in epilepsy surgery, demonstrating broad clinical applications and a favorable safety profile. SEEG, when combined with radiofrequency thermocoagulation (RF-TC), facilitates the identification of epileptogenic zones and serves as a therapeutic option that eliminates the need for general anesthesia, thus incuring no additional costs for patients. This study aimed to investigate whether SEEG-guided RF-TC provides early therapeutic benefits.

METHODS

A retrospective analysis was performed on 44 patients with drug-resistant epilepsy who underwent RF-TC treatment between April 2019 and December 2022, with complete follow-up data available. RF-TC was administered after the recording three or more habitual epileptic seizures in all patients. Demographic characteristics were retrospectively assessed, and treatment outcomes were evaluated using the Engel classification system.

RESULTS

SEEG-guided RF-TC treatment was successfully performed in all patients without significant neurological complications. An average of 7.7 ± 0.4 electrodes were implanted per patient, with a SEEG monitoring duration of 7.5 days (range: 6.8-11). Follow-up after thermocoagulation ranged from 9 to 63 months. At the three-month follow-up, 56.8% of patients achieved Engel I (11 cases) and II (14 cases) were included. At the six-month follow-up, 40.9% of patients achieved Engel grades I (9 cases) and II (9 cases), with five patients proceeding to surgical treatment. By the 12-month follow-up, 40.9% of patients reached Engel grades I (5 cases) and II (13 cases), with a cumulative total of 12 patients undergoing surgical intervention. At the 24-month follow-up, 20.5% of patients achieved Engel grades I (3 cases) and II (6 cases), resulting in a cumulative total of 16 patients undergoing surgical treatment. A statistically significant reduction in seizure frequency was observed before and after thermocoagulation in all 44 patients (P = 0.007), although the therapeutic effect of thermocoagulation decreased over time.

CONCLUSIONS

SEEG-guided RF-TC is a safe and effective treatment modality for drug-resistant epilepsy. However, as follow-up duration increases, both seizure-free rates and response rates following RF-TC progressively decline.

Comparative Efficacy of Surgical Strategies for Drug-Resistant Epilepsy: A Systematic Review and Meta-Analysis

OBJECTIVE

This study evaluated the therapeutic effects of open and minimally invasive surgeries in patients with drug-resistant epilepsy.

METHODS

This study systematically searched electronic databases, including PubMed, Web of Science, Embase, and the Cochrane Library, for randomized controlled trials, subsequent open-label expansion studies, prospective studies and retrospective studies on surgical procedures for patients with drug-resistant epilepsy. The main outcome was seizure-free status. A one-arm meta-analysis integrating data from all studies was performed to evaluate the treatment outcomes at multiple time points.

RESULTS

A total of 62 studies were included, representing 5958 individuals who received five treatment regimens. The analysis results indicate that anterior temporal lobectomy (ATL) and selective amygdalohippocampectomy is still the best choice for treating drug-resistant mesial temporal lobe epilepsy in adult epilepsy patients. During the overall follow-up period, the seizure free rates for ATL, selective amygdalohippocampectomy, laser interstitial thermal therapy, radiofrequency thermocoagulation, and gamma knife surgery were 62%, 70%, 58%, 47%, and 57%, respectively.

CONCLUSIONS

Among the five surgical methods included in this study, ATL and selective amygdala hippocampal resection seem to have more advantages in postoperative epilepsy control compared to laser interstitial hyperthermia, radiofrequency thermocoagulation, and gamma knife surgery. Each surgical treatment method has its unique focus, and when choosing a specific method, it is necessary to consider the patient's specific situation, the type and location of epileptic seizures, and possible side effects. Treating physician will develop personalized treatment plans based on these factors to maximize treatment effectiveness and reduce risks.

Radiofrequency-thermocoagulation in pediatric epilepsy surgery: A systematic review and pooled analysis of cases

OBJECTIVE

To conduct a systematic review on radiofrequency thermocoagulation (RF-TC) in pediatric epilepsy surgery. In addition, due to the low number of dedicated pediatric series, to conduct a pooled analysis of cases published in the literature.

METHODS

We conducted a literature search using PUBMED and EMBASE which produced 432 results. We excluded studies on hypothalamic hamartomas and non-RF-TC procedures such as stereotactic radiosurgery and laser interstitial thermal ablation. Stereotactic RF-TC and SEEG-guided RF-TC procedures were included. Case series and case reports with individualized data were further reviewed and pediatric cases were extracted for pooled analysis. Patient demographics, electroclinical and neuroimaging data, procedure outcomes, responder rates and complications were collected. Our unpublished experience in pediatric SEEG-guided RF-TC was included in the pooled analysis.

RESULTS

We identified 33 articles for the literature review, 24 of them were selected for pooled analysis (93 cases). Sixty patients underwent SEEG-guided RF-TC. For adult and pediatric mixed series reported a 67% responder rate and 32% seizure freedom at 1 year. For exclusively pediatric series, 90% responder rate and 71% Seizure freedom. In the pooled analysis, seizure freedom was achieved in 45.2% and responder rate was 74.2% with a mean follow-up was 25.2 months (SD ± 26.6). Complication rates were low, transient neurological deficits were reported in 18 cases (19.4%) and no deaths were associated with RF-TC. The insula and the dominant frontal lobe were the most frequent targets for ablation. Studies included were highly heterogenous and quality of evidence was low.

SIGNIFICANCE

There are few pediatric studies evaluating RF-TC. Safety and efficacy in children seem to be similar to that reported in larger adult series, although more studies are needed. Most cases reviewed where extracted from heterogeneous adult and pediatric series. Patients with small, high-risk surgical targets are ideal candidates for this procedure.

Stereo-electroencephalography-guided radiofrequency thermocoagulation restricted to periventricular nodular heterotopias in patients with drug-resistant epilepsy: A single center experience

INTRODUCTION

Periventricular nodular heterotopias (PVNH) are developmental abnormalities with neurons abnormally clustered around the cerebral ventricles. Patients frequently present with focal drug-resistant epilepsy (DRE). However, the relationship between PVNH and the seizure onset zone (SOZ) is complex. Stereo-electroencephalography (SEEG) is an invasive diagnostic procedure for patients with DRE. In selected patients, the SEEG may be converted into a therapeutic procedure, lesioning the probable (SOZ) with pulsed radiofrequency thermocoagulation (RFTC). The aim of our study was to evaluate the efficacy and safety of SEEG-RFTC in a series of DRE patients with PVNH.

METHODS

Twenty-four patients with focal DRE related to PVNH and treated with SEEG-guided-RFTC restricted to nodules were prospectively collected between 2016 and 2023 and retrospectively analyzed after a follow-up of at least 12 months.

RESULTS

Seventeen patients (71 %) responded (ILAE class 1-4) after SEEG-guided RFTC of whom eleven (46 %) became seizure-free (class 1) at last follow up, nine (45 %) despite residual PVNH tissue on MRI. SEEG seizure onset was restricted to PVNH in eleven patients (class 1 in 45 %) and simultaneously in PVNH and other cortical areas in thirteen patients (class 1 in 46 %). Out of 31 SEEG-RFTC procedures in twenty-four patients, adverse events, related to RFTC, were recorded in eight (26 %), of which two patients (8 %) had predicted permanent visual complaints whilst the other five had transient complaints.

SIGNIFICANCE

This study demonstrates that a considerable percentage of patients, even with bilateral, multiple PVNH and involvement of adjacent cortical regions can be rendered seizure-free with SEEG-guided-RFTC restricted to the nodules. Furthermore, this study delivers evidence that the complete destruction of the entire nodule is not necessary to render a patient seizure free. This justifies the use of SEEG in patients with single, multiple or bilateral PVNHs to provide insight into the epileptogenic organization in and around these lesions.

Psychiatric complications following SEEG-guided radiofrequency thermocoagulations in patients with drug-resistant epilepsy

SEEG-guided radiofrequency thermocoagulation (RF-TC) in the epileptogenic regions is a therapeutic option for patients with drug-resistant focal epilepsy who may have or not indication for epilepsy surgery. The most common adverse events of RF-TC are seizures, headaches, somatic pain, and sensory-motor deficits. If RF-TC could lead to psychiatric complications is unknown. In the present study, seven out of 164 patients (4.2 %) experienced psychiatric decompensation with or without memory deterioration after RF-TC of bilateral or unilateral amygdala and hippocampus. The appearance of symptoms was either acute, subacute, or chronic and the symptoms were either transient or lasted for several months. Common features among these patients were female sex, mesial temporal epilepsy, and a pre-existing history of psychological distress and memory dysfunction. Our study highlights the possibility of neuropsychiatric deterioration in specific patients following SEEG-guided RF-TC, despite its rarity.

Stereoelectroencephalography-guided radiofrequency thermocoagulation of the epileptogenic zone: a potential treatment and prognostic indicator for subsequent excision surgery

PURPOSE

To evaluate the safety and efficacy of stereoelectroencephalography (SEEG)-guided radiofrequency thermocoagulation (RFTC) for drug-resistant focal epilepsy and investigate the relationship between post-RFTC remission duration and delayed excision surgery effectiveness.

METHODS

We conducted a retrospective analysis of 43 patients with drug-resistant focal epilepsy who underwent RFTC via SEEG electrodes. After excluding three, the remaining 40 were classified into subgroups based on procedures and outcomes. Twenty-four patients (60%) underwent a secondary excision surgery. We determined the predictive value of RFTC outcome upon subsequent surgical outcome by categorizing the delayed secondary surgery outcome as success (Engel I/II) versus failure (Engel III/IV). Demographic information, epilepsy characteristics, and the duration of seizure freedom after RFTC were assessed.

RESULTS

Among 40 patients, 20% achieved Engel class I with RFTC alone, while 24 underwent delayed secondary excision surgery. Overall, 41.7% attained Engel class I, with a 66.7% success rate combining RFTC with delayed surgery. Seizure freedom duration was significantly longer in the success group (mean 4.9 months, SD = 2.7) versus the failure group (mean 1.9 months, SD = 1.1; P = 0.007). A higher proportion of RFTC-only and delayed surgical success group patients had preoperative lesional findings (p = 0.01), correlating with a longer time to seizure recurrence (p < 0.05). Transient postoperative complications occurred in 10%, resolving within a year.

CONCLUSION

This study demonstrates that SEEG-guided RFTC is a safe and potential treatment option for patients with drug-resistant focal epilepsy. A prolonged duration of seizure freedom following RFTC may serve as a predictive marker for the success of subsequent excision surgery.

Predictors of seizure outcomes in stereo-electroencephalography-guided radio-frequency thermocoagulation for MRI-negative epilepsy

Background

One-third of intractable epilepsy patients have no visually identifiable focus for neurosurgery based on imaging tests [magnetic resonance imaging (MRI)-negative cases]. Stereo-electroencephalography-guided radio-frequency thermocoagulation (SEEG-guided RF-TC) is utilized in the clinical treatment of epilepsy to lower the incidence of complications post-open surgery.

Objective

This study aimed to identify prognostic factors and long-term seizure outcomes in SEEG-guided RF-TC for patients with MRI-negative epilepsy.

Design

This was a single-center retrospective cohort study.

Methods

We included 30 patients who had undergone SEEG-guided RF-TC at Sanbo Brain Hospital, Capital Medical University, from April 2015 to December 2019. The probability of remaining seizure-free and the plotted survival curves were analyzed. Prognostic factors were analyzed using log-rank tests in univariate analysis and the Cox regression model in multivariate analysis.

Results

With a mean time of 31.07 ± 2.64 months (median 30.00, interquartile range: 18.00-40.00 months), 11 out of 30 patients (36.7%) were classified as International League Against Epilepsy class 1 in the last follow-up. The mean time of remaining seizure-free was 21.33 ± 4.55 months [95% confidence interval (CI) 12.41-30.25], and the median time was 3.00 ± 0.54 months (95% CI 1.94-4.06). Despite falling in the initial year, the probability of remaining seizure-free gradually stabilizes in the subsequent years. The patients were more likely to obtain seizure freedom when the epileptogenic zone was located in the insular lobe or with one focus on the limbic system (p = 0.034, hazard ratio 5.019, 95% CI 1.125-22.387).

Conclusion

Our findings may be applied to guide individualized surgical interventions and help clinicians make better decisions.

Stereoelectroencephalography-Guided Radiofrequency Thermocoagulation: Diagnostic and Therapeutic Implications

Despite recent medical therapeutic advances, approximately one third of patients do not attain seizure freedom with medications. This drug-resistant epilepsy population suffers from heightened morbidity and mortality. In appropriate patients, resective epilepsy surgery is far superior to continued medical therapy. Despite this efficacy, there remain drawbacks to traditional epilepsy surgery, such as the morbidity of open neurosurgical procedures as well as neuropsychological adverse effects. SEEG-guided Radiofrequency Thermocoagulation (SgRFTC) is a minimally invasive, electrophysiology-guided intervention with both diagnostic and therapeutic implications for drug-resistant epilepsy that offers a convenient adjunct or alternative to ablative and resective approaches. We review the international experience with this procedure, including methodologies, diagnostic benefit, therapeutic benefit, and safety considerations. We propose a framework in which SgRFTC may be incorporated into intracranial EEG evaluations alongside passive recording. Lastly, we discuss the potential role of SgRFTC in both delineating and reorganizing epilepsy networks.

Diffusion spectrum imaging based semi-automatic optic radiation tractography for vision preservation in SEEG-guided radiofrequency thermocoagulation

OBJECTIVE

To assess the efficacy and safety of stereoelectroencephalography (SEEG)-guided radiofrequency thermocoagulation (RFTC), using diffusion spectrum imaging (DSI) tractography to preoperatively delineate the optic radiation (OR) and reduce the risk of visual field defects (VFDs) where the epileptogenic zones (EZs) are located in or close to the eloquent visual areas.

METHODS

We prospectively followed up twenty-four consecutive patients (12 males and 12 females) who underwent SEEG-guided RFTC in or near the OR pathway. A distance of ≥ 3.5 mm away from the OR on the targeted electrodes contacts that exhibited relevant ictal onset patterns, IEDs and EES during SEEG recordings, was required as our selection criterion prior to performing RFTC, enough to theoretically prevent VFDs. Using default tracking parameters, the optic radiation was tracked semi-automatically in DSI-studio.

RESULTS

There were 12 male and 12 female patients ranging in age from 6 to 57 years, with follow-up period ranging from 6 to 37 months. Nineteen patients responded to RFTC (R+, 79.16 %), and 5 patients did not benefit from RFTC (R-, 20.83 %). The preoperative application of DSI semi-automatic based OR tractography was successful in the protection of the OR in all 24 patients. Three patients experienced a neurologic deficit following RFTC, and five patients had a partial quadrant visual field deficit prior to surgery that did not worsen, and none of the remaining nineteen patients had a quadrant visual field deficit.

CONCLUSION

Our study validates the safety and efficacy of SEEG-RFTC as a viable therapeutic approach for epileptic foci situated in or adjacent to the visual eloquent regions. We demonstrate that DSI-based tractography offers superior precision in delineating the OR compared to DTI. We establish that implementing a criterion of a minimum distance of ≥ 3.5 mm in radius from the OR on the targeted electrode contacts prior to conducting RFTC can effectively mitigate the risk of VFDs.

Magnetic resonance-guided laser interstitial thermal therapy vs. stereoelectroencephalography-guided radiofrequency thermocoagulation in epilepsy patients with focal cortical dysplasia: a systematic review and meta-analysis

Background

Magnetic resonance-guided laser interstitial thermal therapy (MRgLiTT) and stereoelectroencephalography-guided radiofrequency thermocoagulation (SEEG-RFTC) are two effective, minimally invasive treatments for epilepsy with focal cortical dysplasia (FCD). The purpose of this study is to conduct a meta-analysis to evaluate and compare the efficacy and safety of these two therapies in epilepsy patients with FCD.

Methods

We searched PubMed, Embase, Cochrane, and other databases for articles published before March 2023. The primary objective was to compare the effectiveness and complications of MRgLiTT and SEEG-RFTC in epilepsy patients with FCD. The second objective was to determine which method provides a better prognosis for specific subgroup patients.

Results

According to the inclusion and exclusion criteria, 18 studies were included, comprising 270 FCD patients including 37 patients from 6 MRgLiTT studies and 233 from 12 SEEG-RFTC studies. There were no significant differences between MRgLiTT and SEEG-RFTC groups in the seizure-freedom rate (59%, 95% CI 44-74%; 52%, 95% CI 47-57%, P = 0.86) and the rate of ≥50% seizure-reduction of FCD (90%, 95% CI 80-100%; 90%, 95% CI 86-94%, P = 0.42). Both methods had low complication rates (17.1%, 28/159) and long-term complication (2.5%, 4/159) rate, with no significant difference between them (P = 0.17).

Conclusion

Both MRgLiTT and SEEG-RFTC are safe and minimally invasive treatments for patients with FCD. They have comparable performance in terms of postoperative seizure-freedom rates in patients with FCD, and both can be used as treatment options for patients with FCD. Our study found that SEEG-RFTC had a better therapeutic effect in the FCD2b subgroup.

Utility of hybrid PET/MRI in stereoelectroencephalography guided radiofrequency thermocoagulation in MRI negative epilepsy patients

Introduction

Hybrid positron emission tomography/magnetic resonance imaging (PET/MRI) is a novel advanced non-invasive presurgical examination tool for patients with drug-resistant epilepsy (DRE). This study aims to evaluate the utility of PET/MRI in patients with DRE who undergo stereoelectroencephalography-guided radiofrequency thermocoagulation (SEEG-guided RFTC).

Methods

This retrospective study included 27 patients with DRE who underwent hybrid PET/MRI and SEEG-guided RFTC. Surgery outcome was assessed using a modified Engel classification, 2 years after RFTC. Potential areas of the seizure onset zone (SOZ) were identified on PET/MRI and confirmed by SEEG.

Results

Fifteen patients (55%) became seizure-free after SEEG-guided RFTC. Engel class II, III, and IV were achieved in six, two, and four patients, respectively at the 2 years follow-up. MRI was negative in 23 patients and structural abnormalities were found in four patients. Hybrid PET/MRI contributed to the identification of new structural or metabolic lesions in 22 patients. Concordant results between PET/MRI and SEEG were found in 19 patients in the identification of SOZ. Among the patients with multifocal onset, seizure-free status was achieved in 50% (6/12).

Conclusion

SEEG-guided RFTC is an effective and safe treatment for drug-resistant epilepsy. Hybrid PET/MRI serves as a useful tool for detecting the potential SOZs in MRI-negative patients and guide the implantation of SEEG electrodes. Patients with multifocal epilepsy may also benefit from this palliative treatment.

Stereo-electroencephalography-guided radiofrequency thermocoagulation in patients with MRI-negative focal epilepsy

OBJECTIVE

Coupled with stereo-electroencephalography (SEEG), radiofrequency thermocoagulation (RFTC) has emerged as a therapeutic alternative for patients with refractory focal epilepsy, with proven safe but highly variable results across studies. The authors aimed to describe the outcomes and safety of SEEG-RFTC, focusing on patients with MRI-negative epilepsy.

METHODS

A retrospective observational study was conducted on patients evaluated by SEEG in the authors' center. Of 84 total cases, 55 underwent RFTC, with 31 MRI-negative epilepsies that were ultimately included in the study. The primary outcome was freedom from disabling seizures at last follow-up. Secondary outcomes were reduction in seizure frequency (RFTC response = seizure frequency reduction > 50%), peri-interventional complications, and neuropsychological outcomes. Potential factors influencing post-RFTC outcome were considered by comparing different variables between responders and nonresponders.

RESULTS

The mean follow-up period was 30.9 months (range 7.1-69.8 months). Three patients underwent subsequent resection/laser interstitial thermal therapy within the 1st year after RFTC failure. All other patients completed a minimum follow-up period of 1 year. Fourteen patients (45.2%) showed at least a 50% reduction in seizure frequency (responders), and 8 were seizure free (25.8% of the whole cohort). One case showed a permanent complication not directly related to thermolesions. Most patients (76%) showed no significant cognitive decline. Electrically elicited seizures (EESs) were observed in all seizure-free patients and were more frequent in responders (p = 0.038). All patients who were seizure free at the 6-month visit maintained their status during long-term follow-up.

CONCLUSIONS

SEEG-RFTC is a safe procedure and leads to a good response in many cases of MRI-negative focal epilepsies. One-quarter of the patients were seizure free and almost one-half were responders at the last follow-up. Although these results are still far from those achieved through conventional resection, a nonnegligible proportion of patients may benefit from this one-stage and much less invasive approach. Factors associated with seizure outcome remain to be elucidated; however, responders were significantly more frequent among patients with EESs, and achieving 6 months of seizure freedom appears to predict a good long-term response. In addition, the positive predictive value of RFTC response may be a valuable factor in the decision to proceed to subsequent surgery.

Systematic review and patient-level meta-analysis of radiofrequency ablation for medically refractory epilepsy: Implications for clinical practice and research

BACKGROUND

Radiofrequency thermocoagulation (RF-TC) is a minimally invasive procedure for the treatment of epileptic foci. The aim of this study is to review available evidence on the safety and efficacy of RF-TC for medically refractory epilepsy.

METHODS

A comprehensive literature search (Pubmed/Medline, EMBASE, Cochrane) was conducted for studies with patient-level data on RF-TC for medically refractory epilepsy. Seizure outcome (Engel classification) at last follow-up comprised the primary endpoint. New temporary or permanent post-procedural neurological deficits were the secondary endpoints.

RESULTS

A total of 20 studies (360 patients) were analyzed. Median age at the time of intervention was 29 years (interquartile range (IQR): 21-37) and 57% were males. A lesional MRI was noted in 59% of patients. Median duration of postoperative follow-up was 24 months (IQR: 11-48). The median number of RF-TC lesions per patient was 11 (IQR: 6-19), with bipolar ablation (i.e. between two contiguous contacts) being the most common method (n = 244, 68%). The most common RF-TC location was the mesial temporal structures, without (34%) or with (7%) the temporal neocortex, followed by the insula (13%) and the frontal lobe (12%). Multilobar targets were lesioned in 11% of patients. New neurological deficits developed in 10% of patients (2% remained permanently), with the most common being motor deficits. Among patients with at least 12 months of follow-up (n = 267, 74% of overall cohort), a favorable seizure outcome (Engel I/II class) was achieved in 62% of cases. Patients with a favorable seizure outcome were significantly more likely to have a lesional MRI (71% vs 43% 51%, p < 0.001), have a higher number of RF ablations (15 [IQR 8-31] vs 9 [IQR 4-14], p < 0.001), and undergo monopolar RF-TC (50% vs 30%, p = 0.002).

CONCLUSION

Current evidence supports the promising safety and efficacy profile of RF-TC for medically refractory epilepsy. Randomized controlled trial data are needed to further establish the role of this intervention in preoperative discussions with patients and their families.

Advances in human intracranial electroencephalography research, guidelines and good practices

Since the second-half of the twentieth century, intracranial electroencephalography (iEEG), including both electrocorticography (ECoG) and stereo-electroencephalography (sEEG), has provided an intimate view into the human brain. At the interface between fundamental research and the clinic, iEEG provides both high temporal resolution and high spatial specificity but comes with constraints, such as the individual's tailored sparsity of electrode sampling. Over the years, researchers in neuroscience developed their practices to make the most of the iEEG approach. Here we offer a critical review of iEEG research practices in a didactic framework for newcomers, as well addressing issues encountered by proficient researchers. The scope is threefold: (i) review common practices in iEEG research, (ii) suggest potential guidelines for working with iEEG data and answer frequently asked questions based on the most widespread practices, and (iii) based on current neurophysiological knowledge and methodologies, pave the way to good practice standards in iEEG research. The organization of this paper follows the steps of iEEG data processing. The first section contextualizes iEEG data collection. The second section focuses on localization of intracranial electrodes. The third section highlights the main pre-processing steps. The fourth section presents iEEG signal analysis methods. The fifth section discusses statistical approaches. The sixth section draws some unique perspectives on iEEG research. Finally, to ensure a consistent nomenclature throughout the manuscript and to align with other guidelines, e.g., Brain Imaging Data Structure (BIDS) and the OHBM Committee on Best Practices in Data Analysis and Sharing (COBIDAS), we provide a glossary to disambiguate terms related to iEEG research.

Volume-Based Radiofrequency Thermocoagulation for Pediatric Insulo-Opercular Epilepsy: A Feasibility Study

BACKGROUND

Stereotactic ablation surgeries including radiofrequency thermocoagulation (RFTC) and laser interstitial thermal therapy are recent less invasive treatment methods for insular epilepsy. Volume-based RFTC after stereoelectroencephalography was first proposed by a French group as a more effective method for seizure relief in insular epilepsy patients than stereoelectroencephalography-guided RFTC.

OBJECTIVE

To describe the feasibility and technical details about volume-based RFTC in patients with insulo-opercular epilepsy.

METHODS

We successfully treated 3- and 6-year-old patients with medically refractory insulo-opercular epilepsy with volume-based RFTC, in which the target volume of coagulation was flexibly designed by combining multiple spherical models of 5-mm diameter which is smaller than reported previously.

RESULTS

The insula was targeted by oblique trajectory from the frontoparietal area in one case, and the opercular cortex was targeted by perpendicular trajectories from the perisylvian cortex in the other case. The use of the small sphere model required more trajectories and manipulations but enabled more exhaustive coagulation of the epileptogenic zone, with 70% to 78% of the planned target volume coagulated without complications, and daily seizures disappeared after RFTC in both patients.

CONCLUSION

Volume-based RFTC planned with small multiple sphere models may improve the completeness of lesioning for patients with insulo-opercular epilepsy. Careful planning is necessary to reduce the risks of vascular injuries.

Surgical approaches to refractory central lobule epilepsy: a systematic review on the role of resection, ablation, and stimulation in the contemporary era

OBJECTIVE

Epilepsy originating from the central lobule (i.e., the primary sensorimotor cortex) is a challenging entity to treat given its involvement of eloquent cortex. The objective of this study was to review available evidence on treatment options for central lobule epilepsy.

METHODS

A comprehensive literature search (PubMed/Medline, EMBASE, and Scopus) was conducted for studies (1990 to date) investigating postoperative outcomes for central lobule epilepsy. The primary and secondary endpoints were seizure freedom at last follow-up and postoperative neurological deficit, respectively. The following procedures were included: open resection, multiple subpial transections (MSTs), laser and radiofrequency ablation, deep brain stimulation (DBS), responsive neurostimulation (RNS), and continuous subthreshold cortical stimulation (CSCS).

RESULTS

A total of 52 studies and 504 patients were analyzed. Most evidence was based on open resection, yielding a total of 400 patients (24 studies), of whom 62% achieved seizure freedom at a mean follow-up of 48 months. A new or worsened motor deficit occurred in 44% (permanent in 19%). Forty-six patients underwent MSTs, of whom 16% achieved seizure freedom and 30% had a neurological deficit (permanent in 12%). There were 6 laser ablation cases (cavernomas in 50%) with seizure freedom in 4 patients and 1 patient with temporary motor deficit. There were 5 radiofrequency ablation cases, with 1 patient achieving seizure freedom, 2 patients each with Engel class III and IV outcomes, and 2 patients with motor deficit. The mean seizure frequency reduction at the last follow-up was 79% for RNS (28 patients), 90% for CSCS (15 patients), and 73% for DBS (4 patients). There were no cases of temporary or permanent neurological deficit in the CSCS or DBS group.

CONCLUSIONS

This review highlights the safety and efficacy profile of resection, ablation, and stimulation for refractory central lobe epilepsy. Resection of localized regions of epilepsy onset zones results in good rates of seizure freedom (62%); however, nearly 20% of patients had permanent motor deficits. The authors hope that this review will be useful to providers and patients when tailoring decision-making for this intricate pathology.

Stereoelectroencephalography-Guided Radiofrequency Thermocoagulation of Epileptic Foci in the Eloquent Motor Cortex: Feasibility, Safety, and Efficacy

OBJECTIVE

To assess safety and long-term outcome of stereoelectroencephalography (SEEG)-guided radiofrequency thermocoagulation (RFTC) of epileptic foci in eloquent motor areas.

METHODS

We retrospectively reviewed medical charts and surgical features of 15 patients with drug-resistant focal epilepsy in eloquent motor areas treated between 2017 and 2021. All patients underwent SEEG-guided RFTC as the first option. General characteristics, SEEG findings, morbidity, and seizure outcome after RFTC were analyzed to extract the potential value of SEEG-guided RFTC for epileptic foci in eloquent motor areas.

RESULTS

There were 12 male and 3 female patients. Mean age at RFTC was 25 ± 8.5 years (range, 14-48 years), and mean duration of epilepsy before SEEG was 9.5 ± 7.0 years (range, 2-26 years). Mean follow-up period was 22.1 months (range, 8-41 months). Magnetic resonance imaging findings were negative in 2 cases, suspected focal cortical dysplasia in 10 cases, central region band heterotopias in 2 cases, and malformations of cortical development in 1 case. RFTC sites included primary precentral area (M1) (7, 46.7%), paracentral lobule (4, 26.7%), supplemental motor area (2, 13.3%), and premotor area (2, 13.3%). Of 15 patients, 12 (80%) experienced a ≥75% decrease in seizure frequency, of whom 9 (60%) experienced a long-term seizure-free period (10-29 months, mean 21.3 months). Three (20%) patients did not benefit from RFTC. Nine patients had neurological deficits immediately after RFTC (transient in 8 patients [3 days to 3 weeks] and prolonged in 1 patient).

CONCLUSIONS

SEEG-guided RFTC for epileptic foci in eloquent motor areas seems to be a safe and effective procedure. It could be the first option for drug-resistant epilepsy that is not amenable to surgical resection, especially for extremally focused epileptic foci in the cortex close to or inside the central region. Larger series and prospective studies are necessary to validate our conclusions.

Optimization and high-density array of stereoelectroencephalography-guided radiofrequency thermocoagulation for the treatment of pediatric tuberous sclerosis complex with epilepsy

BACKGROUND

Tuberous sclerosis complex (TSC) is an autosomal dominant neurocutaneous syndrome involved in many organ systems. At the same time, epilepsy is the most common manifestation and more than 50% of TSC patients present with intractable epilepsy. This study investigated the efficacy and safety of optimized and high-density stereoelectroencephalography (SEEG) guided radiofrequency thermocoagulation (RF-TC) in treating TSC-related epilepsy.

METHODS

Nine TSC children with refractory epilepsy were treated with first-stage SEEG-Guided RF-TC, and four underwent second-stage-optimized high-density array of SEEG-Guided RF-TC. Patients' clinical data and postoperative outcomes were analyzed retrospectively.

RESULTS

The patients' median age at surgery was 4 years and 2 month (range from 3 years and 5 month to 16 years and 7 month). The mean age at surgery was 6.7 years old. Eight in 9 (88.9%) patients achieved complete remission after the final operation at half-year follow-up. Of seven patients with final postoperative time beyond 1 year, 6 (85.7%) reached completely seizure-free. No severe or long-term neurologic impairment existed in all nine patients.

CONCLUSION

Optimized high-density array of SEEG-guided RF-TC is a safe and highly effective approach and can be an alternative application applied for TSC patients with refractory epilepsy.

Theoretical stereoelectroencephalography density on the brain convexity

INTRODUCTION

Invasive electroencephalography (EEG) remains the "gold standard" for diagnosing the epileptogenic zone in patients with drug-resistant epilepsy and discrepancies between seizure semiology, video-EEG and magnetic resonance imaging (MRI) findings. However, the possibilities of stereoelectroencephalography (SEEG) to explore the brain surface remain a matter of debate and subdural EEG (SDEEG) is still preferred in some centers for cases when the supposed epileptogenic zone is on the brain convexity. The aim of our study was to evaluate the theoretical safe SEEG coverage on the brain convexity and to compare the theoretical SEEG cortical density with the usual SDEEG density.

MATERIALS AND METHODS

Our material included 10 hemispheres in 5 patients, who had been already investigated with SEEG for drug-resistant epilepsy. We translated our previously described technique in a theoretical model in an attempt to calculate the maximal number of avascular windows for each cerebral hemisphere. The distance between every entry point and the other entry points for each hemisphere was calculated using a mathematical formula. Subsequently, the theoretical SEEG coverage on the brain convexity was described using the maximal, minimal and average distances between each entry point and the closest 4 neighboring points. This type of measurement allows a direct comparison between SEEG and SDEEG in their ability to explore the brain convexity.

RESULTS

Ten hemispheres had 1328 safe entry points with a safety margin of 2.5 mm and a minimal distance of 2.5 mm between 2 entry points (average number of entry points: 132.8 (SD ± 5). The number of entry points in the explored 10 hemispheres varied from 104 to 156. The average distance between each entry point and its 4 neighbors was 11.47 mm. The maximal distance between two entry points in these 10 hemispheres was ranging from 20.28 to 27.23 mm (average: 24.67 mm). The closest entry points for the explored hemispheres were at an average distance of 4.67 mm (range: 2.82 - 5.96 mm). The average convexity surface was 223.68 cm2 (range: 204.63-238.77 cm2). The safe electrode density without electrode collision on the cortical surface was ranging from 0.46 to 0.69 electrodes per cm2 (average: 0.59 electrodes per cm2) (SD ± 0.023).

CONCLUSION

The theoretical SEEG cortical density is comparable with the usual SDEEG density. These findings, combined with the better safety profile of SEEG and the possibilities to explore deep cortical structures, explain the progressive shift from SDEEG to SEEG during the last years.

Smaller Knife, Fewer Seizures? Recent Advances in Minimally Invasive Techniques in Pediatric Epilepsy Surgery

Children with drug-resistant epilepsy are at high risk for developmental delay, increased mortality, psychiatric comorbidities, and requiring assistance with activities of daily living. Despite the advent of new and effective pharmacologic therapies, about one in 5 children will develop drug-resistant epilepsy, and most of these children continue to have seizures despite trials of other medication. Epilepsy surgery is often a safe and effective option which may offer seizure freedom or at least a significant reduction in seizure burden in many children. However, despite published evidence of safety and efficacy, epilepsy surgery remains underutilized in the pediatric population. Patient and family fears about the risks of surgery may contribute to this gap. Less invasive surgical techniques may be more palatable to children with epilepsy and their caregivers. In this review, we present recent advances in minimally invasive techniques for the surgical treatment of epilepsy as well as intriguing possibilities for the future. We describe the indications for, benefits of, and limits to minimally-invasive techniques including Stereo-encephalography, laser interstitial thermal ablation, deep brain stimulation, focused ultrasound, stereo-encephalography-guided radiofrequency ablation, endoscopic disconnections, and responsive neurostimulation.

Changes in epileptogenicity biomarkers after stereotactic thermocoagulation

OBJECTIVE

Stereo-electroencephalography (SEEG)-guided radiofrequency thermocoagulation (RF-TC) aims at modifying epileptogenic networks to reduce seizure frequency. High-frequency oscillations (HFOs), spikes, and cross-rate are quantifiable epileptogenic biomarkers. In this study, we sought to evaluate, using SEEG signals recorded before and after thermocoagulation, whether a variation in these markers is related to the therapeutic effect of this procedure and to the outcome of surgery.

METHODS

Interictal segments of SEEG signals were analyzed in 38 patients during presurgical evaluation. We used an automatized method to quantify the rate of spikes, rate of HFOs, and cross-rate (a measure combining spikes and HFOs) before and after thermocoagulation. We analyzed the differences both at an individual level with a surrogate approach and at a group level with analysis of variance. We then evaluated the correlation between these variations and the clinical response to RF-TC and to subsequent resective surgery.

RESULTS

After thermocoagulation, 19 patients showed a clinical improvement. At the individual level, clinically improved patients more frequently had a reduction in spikes and cross-rate in the epileptogenic zone than patients without clinical improvement (p = .002, p = .02). At a group level, there was a greater decrease of HFOs in epileptogenic and thermocoagulated zones in patients with clinical improvement (p < .05) compared to those with no clinical benefit. Eventually, a significant decrease of all the markers after RF-TC was found in patients with a favorable outcome of resective surgery (spikes, p = .026; HFOs, p = .03; cross-rate, p = .03).

SIGNIFICANCE

Quantified changes in the rate of spikes, rate of HFOs, and cross-rate can be observed after thermocoagulation, and the reduction of these markers correlates with a favorable clinical outcome after RF-TC and with successful resective surgery. This may suggest that interictal biomarker modifications after RF-TC can be clinically used to predict the effectiveness of the thermocoagulation procedure and the outcome of resective surgery.

Network radiofrequency ablation for drug resistant epilepsy

Radiofrequency ablation (RFA) is a minimally invasive procedure for drug-resistant focal epilepsy. Although well tolerated, seizure outcomes are less favorable than standard resection. RFA is commonly performed following stereoencephalography (sEEG) identification of the seizure onset zone (SOZ). We hypothesized RFA outcomes can improve by adding RFA of seizure spread regions to the SOZ as identified by sEEG, an approach we term network RFA. Four patients underwent network RFA at our institution from 8/2017 to 9/2019. There were two Engel IB outcomes and two Engel III outcomes. The median follow-up length was 25.5 months (range 17-35). No permanent neurological deficits occurred. Etiologies consisted of polymicrogyria (1), mixed malformation of cortical development (MCD) (2), and cryptogenic (1). This study provides descriptive results regarding the efficacy and safety of network RFA. Network RFA can be considered in patients with focal epilepsies with large MCDs that may not be amenable to standard resection.

Focal lesions induce large-scale percolation of sleep-like intracerebral activity in awake humans

Focal cortical lesions are known to result in large-scale functional alterations involving distant areas; however, little is known about the electrophysiological mechanisms underlying these network effects. Here, we addressed this issue by analysing the short and long distance intracranial effects of controlled structural lesions in humans. The changes in Stereo-Electroencephalographic (SEEG) activity after Radiofrequency-Thermocoagulation (RFTC) recorded in 21 epileptic subjects were assessed with respect to baseline resting wakefulness and sleep activity. In addition, Cortico-Cortical Evoked Potentials (CCEPs) recorded before the lesion were employed to interpret these changes with respect to individual long-range connectivity patterns. We found that small structural ablations lead to the generation and large-scale propagation of sleep-like slow waves within the awake brain. These slow waves match those recorded in the same subjects during sleep, are prevalent in perilesional areas, but can percolate up to distances of 60 mm through specific long-range connections, as predicted by CCEPs. Given the known impact of slow waves on information processing and cortical plasticity, demonstrating their intrusion and percolation within the awake brain add key elements to our understanding of network dysfunction after cortical injuries.

Radiofrequency Thermocoagulation in Refractory Focal Epilepsy: The Montreal Neurological Institute Experience

BACKGROUND

Radiofrequency thermocoagulation (RF-TC) is a minimally invasive ablative option for refractory focal epilepsy.

METHODS

A retrospective chart review was conducted of all patients who underwent stereoelectroencephalography (SEEG)-guided RF-TC at our institution.

RESULTS

Fourteen patients underwent robot-guided electrode implantation and subsequent RF-TC. After RF-TC, one of the three patients with PVNH was seizure free, one had 18 months of seizure freedom (Engel 2b), and one required temporal neocortical/PVNH resection (Engel 1a). One of the four patients with focal cortical dysplasia (FCD) was seizure free (Engel 1a), two attained seizure freedom after resection (Engel 1a and 1b), while one continues to have significant seizures (Engel 4b). One patient with cavernoma and low central area epileptogenic zone (EZ) did not benefit from RF-TC and is planned for resection. Two of the MRI-negative patients achieved seizure freedom for 3 months and 1 year, respectively, subsequently requiring resection (Engel 1a). One remains seizure free at 4 weeks. Three had seizure recurrence immediately (Engel 4b). With RF-TC alone, two patients (14%) achieved Engel 1a, two were seizure free at 1 year, one had 3 months of seizure freedom, while the rest had recurrence immediately or within a few weeks. 7/14 patients underwent secondary interventions after RF-TC. Overall, seven patients achieved Engel 1a or 1b, one each 2b and 3a, and five Engel 4b.

CONCLUSION

At our institution, RF-TC is a safe ablative procedure for refractory focal epilepsy. It can serve as a segue to secondary interventions and appears promising in PVNH cases. Its role in MRI-negative cases is less clear.

Treatment of Epilepsy Associated with Periventricular Nodular Heterotopia

PURPOSE OF REVIEW

Epilepsy associated with periventricular nodular heterotopia (PNH), a developmental malformation, is frequently drug-resistant and requires focal therapeutic intervention. Invasive EEG study is usually necessary to delineate the epileptogenic zone, but constructing an accurate hypothesis to define an appropriate electrode implantation scheme and the treatment is challenging. This article reviews recent studies that help understanding the epileptogenicity and potential therapeutic options in PNH.

RECENT FINDINGS

New noninvasive diagnostic and intracerebral EEG analytic tools demonstrated that cortical hyperexcitability and aberrant connectivity (between nodules and cortices and among nodules) are likely mechanisms causing epilepsy in most patients. The deeply seated PNH, if epileptogenic, are ideal target for stereotactic ablative techniques, which offer concomitant ablation of multiple regions with relatively satisfactory seizure outcome. Advance in diagnostic and analytic tools have enhanced our understanding of the complex epileptogenicity in PNH. Development in stereotactic ablative techniques now offers promising therapeutic options for these patients.

Indications, Techniques, and Outcomes of Robot-Assisted Insular Stereo-Electro-Encephalography: A Review

Stereo-electro-encephalography (SEEG) is an invasive, surgical, and electrophysiological method for three-dimensional registration and mapping of seizure activity in drug-resistant epilepsy. It allows the accurate analysis of spatio-temporal seizure activity by multiple intraparenchymal depth electrodes. The technique requires rigorous non-invasive pre-SEEG evaluation (clinical, video-EEG, and neuroimaging investigations) in order to plan the insertion of the SEEG electrodes with minimal risk and maximal recording accuracy. The resulting recordings are used to precisely define the surgical limits of resection of the epileptogenic zone in relation to adjacent eloquent structures. Since the initial description of the technique by Talairach and Bancaud in the 1950's, several techniques of electrode insertion have been used with accuracy and relatively few complications. In the last decade, robot-assisted surgery has emerged as a safe, accurate, and time-saving electrode insertion technique due to its unparalleled potential for orthogonal and oblique insertion trajectories, guided by rigorous computer-assisted planning. SEEG exploration of the insular cortex remains difficult due to its anatomical location, hidden by the temporal and frontoparietal opercula. Furthermore, the close vicinity of Sylvian vessels makes surgical electrode insertion challenging. Some epilepsy surgery teams remain cautious about insular exploration due to the potential of neurovascular injury. However, several authors have published encouraging results regarding the technique's accuracy and safety in both children and adults. We will review the indications, techniques, and outcomes of insular SEEG exploration with emphasis on robot-assisted implantation.

Outcomes of stereoelectroencephalography exploration at an epilepsy surgery center

OBJECTIVES

Epilepsy surgery is offered in resistant focal epilepsy. Non-invasive investigations like scalp video EEG monitoring (SVEM) help delineate epileptogenic zone. Complex cases may require intracranial video EEG monitoring (IVEM). Stereoelectroencephalography (SEEG)-based intracerebral electrode implantation has better spatial resolution, lower morbidity, better tolerance, and superiority in sampling deep structures. Our objectives were to assess IVEM using SEEG with regard to reasoning behind implantation, course, surgical interventions, and outcomes.

MATERIALS AND METHODS

Seventy-two admissions for SEEG from January 2014 to December 2018 were included in the study. Demographic and clinical data were retrospectively collected.

RESULTS

The cohort comprised of 69 adults of which 34 (47%) had lesional MRI. Reasons for SEEG considering all cases included non-localizing ictal onset (76%), ictal-interictal discordance (21%), discordant semiology (17%), proximity to eloquent cortex (33%), nuclear imaging discordance (34%), and discordance with neuropsychology (19%). Among lesional cases, additional reasons included SVEM discordance (68%) and dual or multiple pathology (47%). Forty-eight patients (67%) were offered resective surgery, and 41 underwent it. Twenty-three (56%) had at least one year post-surgical follow-up of which 14 (61%) had Engels class I outcome. Of the remaining 23 who were continued on medical management, 4 (17%) became seizure-free and 12 (51%) had reduction in seizure frequency.

CONCLUSION

SEEG monitoring is an important and safe tool for presurgical evaluation with good surgical and non-surgical outcomes. Whether seizure freedom following non-surgical management could be related to SEEG implantation, medication change, or natural course needs to be determined.

Value of stereoelectroencephalography (SEEG)-guided radiofrequency thermocoagulation in treating drug-resistant focal epilepsy

Stereoelectroencephalography (SEEG) has been widely used in the presurgical evaluation of patients with medically intractable epilepsy. In the past, SEEG was commonly used as a method for mapping and localizing the epileptogenic zone (EZ). Since 2004, several studies have been conducted to examine the effectiveness of SEEG-guided radiofrequency thermocoagulation (RF-TC) in treating refractory epilepsy. However, the seizure-free and responder rates varied greatly across studies. We aimed to analyze the outcome of 56 patients who were treated with SEEG-guided RF-TC to evaluate the effectiveness of this treatment. SEEG-guided RF-TC can be considered as a treatment for refractory epilepsy. However, due to its limited efficacy, SEEG-guided RF-TC might be regarded as a temporary treatment performed under SEEG rather than a promising treatment for refractory epilepsy.

The value of magnetoencephalography for stereo-EEG-guided radiofrequency thermocoagulation in MRI-negative epilepsy

OBJECTIVE

Magnetoencephalography (MEG) is valuable for guiding resective surgery in patients with epilepsy. However, its value for minimally invasive treatment is still unknown. This study aims to evaluate the value of MEG for stereo-electroencephalogram (EEG)-guided radiofrequency thermocoagulation (SEEG-guided RF-TC) in magnetic resonance imaging (MRI)-negative epilepsies.

METHODS

An observational cohort study was performed and 19 MRI-negative patients who underwent SEEG-guided RF-TC in our epilepsy center were included. In addition, 16 MRI-positive patients were included as a reference group. Semiology, electrophysiology, and imaging information were collected. To evaluate the value of locating the MEG cluster, the proportion of the RF-TC contacts located in the MEG cluster out of all contacts used to perform RF-TC in each patient was calculated. All patients underwent the standard SEEG-guided RF-TC procedure and were followed up after the treatment.

RESULTS

Nineteen MRI-negative patients were divided into two groups based on the existence of MEG clusters; 10 patients with MEG clusters were in group I and nine patients without any MEG cluster were in group II. No significant difference was observed in terms of age, sex, type of seizures, or number of SEEG electrodes implanted. The median of the proportion of contacts in the MEG cluster was 77.0 % (IQR 57.7-100.0 %). The follow-up results showed that the probability of being seizure-free at one year after RFTC in MRI-negative patients with an MEG cluster was 30.0 % (95 % CI 11.6-77.3 %), significantly (p = 0.014) higher than that in patients without an MEG cluster; there was no significant difference when compared with MRI-positive patients.

CONCLUSION

This is the first study to evaluate the value of MEG in SEEG-guided RF-TC in MRI-negative epilepsies. MEG is a useful supplement for patients with MRI-negative epilepsy. MEG can be applied in minimally invasive treatment. MEG clusters can help identify better candidates and provide a valuable target for SEEG-guided RF-TC, which leads to better outcomes.

Presurgical epilepsy evaluation and epilepsy surgery

With a prevalence of 0.8 to 1.2%, epilepsy represents one of the most frequent chronic neurological disorders; 30 to 40% of patients suffer from drug-resistant epilepsy (that is, seizures cannot be controlled adequately with antiepileptic drugs). Epilepsy surgery represents a valuable treatment option for 10 to 50% of these patients. Epilepsy surgery aims to control seizures by resection of the epileptogenic tissue while avoiding neuropsychological and other neurological deficits by sparing essential brain areas. The most common histopathological findings in epilepsy surgery specimens are hippocampal sclerosis in adults and focal cortical dysplasia in children. Whereas presurgical evaluations and surgeries in patients with mesial temporal sclerosis and benign tumors recently decreased in most centers, non-lesional patients, patients requiring intracranial recordings, and neocortical resections increased. Recent developments in neurophysiological techniques (high-density electroencephalography [EEG], magnetoencephalography, electrical and magnetic source imaging, EEG-functional magnetic resonance imaging [EEG-fMRI], and recording of pathological high-frequency oscillations), structural magnetic resonance imaging (MRI) (ultra-high-field imaging at 7 Tesla, novel imaging acquisition protocols, and advanced image analysis [post-processing] techniques), functional imaging (positron emission tomography and single-photon emission computed tomography co-registered to MRI), and fMRI significantly improved non-invasive presurgical evaluation and have opened the option of epilepsy surgery to patients previously not considered surgical candidates. Technical improvements of resective surgery techniques facilitate successful and safe operations in highly delicate brain areas like the perisylvian area in operculoinsular epilepsy. Novel less-invasive surgical techniques include stereotactic radiosurgery, MR-guided laser interstitial thermal therapy, and stereotactic intracerebral EEG-guided radiofrequency thermocoagulation.

Multiple Stereoelectroencephalography-Guided Radiofrequency Thermocoagulations for Polymicrogyria With Startle Seizures: A Case Report

The best results of stereoelectroencephalography (SEEG)-guided radiofrequency thermocoagulation (RF-TC) were observed in epilepsies with more limited lesions, but this procedure is rarely used in a wide range of brain malformation. We report a rare case of polymicrogyria (PMG) combined with drug-resistant startle seizures. Presurgical monitoring was performed using SEEG owing to the large lesion and complexity of PMG. According to the intracranial electrode results, the seizure onset was extensive, with the onset starting earlier in the cingulate sulcus and insular pole than in other sites of the other electrodes. Multi-point and multi-step SEEG-guided RF-TC was used for diffuse lesion and functional protection. RF-TC was first applied to the cingulate sulcus and insular pole, and our patient was rendered free from startle seizures after 2 weeks. Two weeks of observation helped us to observe the efficacy of RF-TC and the changes of SEEG, so as to make the next TC scheme. The patient still had spontaneous seizures after the first treatment. RF-TC was then applied to other sites involved earlier. Finally, the patient reached Engel class IIa for a follow-up period of 1 year. There were no additional startle seizures, and important functional areas were protected.

Efficacy of limited hippocampal radiofrequency thermocoagulation for mesial temporal lobe epilepsy

OBJECTIVE

Radiofrequency thermocoagulation (RFTC), which has been developed for drug-resistant epilepsy patients, involves less brain tissue loss due to surgery, fewer surgical adverse effects, and generally good seizure control. This study demonstrates the effectiveness of RFTC performed at limited hippocampal locations.

METHODS

Daily seizure diaries were prospectively maintained for at least 6 months by 9 patients (ages 30-59 years) with drug-resistant mesial temporal lobe epilepsy (MTLE) before treatment with RFTC. The limited target for stereotactic RFTC was chosen based on intraoperative electroencephalography (EEG) recording and was initially tested with a Radionics electrode at a low temperature, 45°C, for 60 seconds. The therapeutic RFTC heating parameters were 78°C-80°C for 90 seconds. All patients who received the RFTC treatment underwent both MRI and EEG recording immediately postoperatively and at the 3-month follow-up. Monthly outpatient clinic visits were arranged over 6 months to document seizure frequency and severity to clarify the changes noted in imaging studies and EEG patterns.

RESULTS

Two patients were excluded from our analysis because one had undergone multiple seizure surgeries and the other had a poor recording of seizure frequency, before the RFTC surgery. Five and two patients underwent left-sided and right-sided RFTC, respectively. None of the patients had generalized tonic-clonic attacks postoperatively, and no adverse effects or complications occurred. According to MRI data, the effect of coagulation was limited to less than 1.0 cm in diameter and perifocal edema was also in limited range. The seizure frequency within 6 months decreased postoperatively with a mean reduction in seizures of 78% (range 36%-100%). Only two patients had a temporary increase in seizure frequency within 2 weeks of the surgery, and over 50% of all patients showed a decrease in average seizure frequency.

CONCLUSIONS

The study results confirm that limited RFTC provides a more effective surgery with similar seizure control but fewer complications than resective surgery for drug-resistant MTLE patients.

Association of Cortical Stimulation-Induced Seizure With Surgical Outcome in Patients With Focal Drug-Resistant Epilepsy

Importance

Cortical stimulation is used during presurgical epilepsy evaluation for functional mapping and for defining the cortical area responsible for seizure generation. Despite wide use of cortical stimulation, the association between cortical stimulation-induced seizures and surgical outcome remains unknown.

Objective

To assess whether removal of the seizure-onset zone resulting from cortical stimulation is associated with a good surgical outcome.

Design, Setting, and Participants

This cohort study used data from 2 tertiary epilepsy centers: Montreal Neurological Institute in Montreal, Quebec, Canada, and Grenoble-Alpes University Hospital in Grenoble, France. Participants included consecutive patients (n = 103) with focal drug-resistant epilepsy who underwent stereoelectroencephalography between January 1, 2007, and January 1, 2017. Participant selection criteria were cortical stimulation during implantation, subsequent open surgical procedure with a follow-up of 1 or more years, and complete neuroimaging data sets for superimposition between intracranial electrodes and the resection.

Main Outcomes and Measures

Cortical stimulation-induced typical electroclinical seizures, the volume of the surgical resection, and the percentage of resected electrode contacts inducing a seizure or encompassing the cortical stimulation-informed and spontaneous seizure-onset zones were identified. These measures were correlated with good (Engel class I) and poor (Engel classes II-IV) surgical outcomes. Electroclinical characteristics associated with cortical stimulation-induced seizures were analyzed.

Results

In total, 103 patients were included, of whom 54 (52.4%) were female, and the mean (SD) age was 31 (11) years. Fifty-nine patients (57.3%) had cortical stimulation-induced seizures. The percentage of patients with cortical stimulation-induced electroclinical seizures was higher in the good outcome group than in the poor outcome group (31 of 44 [70.5%] vs 28 of 59 [47.5%]; P = .02). The percentage of the resected contacts encompassing the cortical stimulation-informed seizure-onset zone correlated with surgical outcome (median [range] percentage in good vs poor outcome: 63.2% [0%-100%] vs 33.3% [0%-84.6%]; Spearman ρ = 0.38; P = .003). A similar result was observed for spontaneous seizures (median [range] percentage in good vs poor outcome: 57.1% [0%-100%] vs 32.7% [0%-100%]; Spearman ρ = 0.32; P = .002). Longer elapsed time since the most recent seizure was associated with a higher likelihood of inducing seizures (>24 hours: 64.7% vs <24 hours: 27.3%; P = .04).

Conclusions and Relevance

Seizure induction by cortical stimulation appears to identify the epileptic generator as reliably as spontaneous seizures do; this finding might lead to a more time-efficient intracranial presurgical investigation of focal epilepsy as the need to record spontaneous seizures is reduced.

Stereoelectroencephalography: retrospective analysis of 742 procedures in a single centre

This retrospective description of a surgical series is aimed at reporting on indications, methodology, results on seizures, outcome predictors and complications from a 20-year stereoelectroencephalography (SEEG) activity performed at a single epilepsy surgery centre. Prospectively collected data from a consecutive series of 742 SEEG procedures carried out on 713 patients were reviewed and described. Long-term seizure outcome of SEEG-guided resections was defined as a binomial variable: absence (ILAE classes 1–2) or recurrence (ILAE classes 3–6) of disabling seizures. Predictors of seizure outcome were analysed by preliminary uni/bivariate analyses followed by multivariate logistic regression. Furthermore, results on seizures of these subjects were compared with those obtained in 1128 patients operated on after only non-invasive evaluation. Survival analyses were also carried out, limited to patients with a minimum follow-up of 10 years. Resective surgery has been indicated for 570 patients (79.9%). Two-hundred and seventy-nine of 470 patients operated on (59.4%) were free of disabling seizures at least 2 years after resective surgery. Negative magnetic resonance and post-surgical lesion remnant were significant risk factors for seizure recurrence, while type II focal cortical dysplasia, balloon cells, glioneuronal tumours, hippocampal sclerosis, older age at epilepsy onset and periventricular nodular heterotopy were significantly associated with seizure freedom. Twenty-five of 153 patients who underwent radio-frequency thermal coagulation (16.3%) were optimal responders. Thirteen of 742 (1.8%) procedures were complicated by unexpected events, including three (0.4%) major complications and one fatality (0.1%). In conclusion, SEEG is a safe and efficient methodology for invasive definition of the epileptogenic zone in the most challenging patients. Despite the progressive increase of MRI-negative cases, the proportion of seizure-free patients did not decrease throughout the years.

Stereoelectroencephalography in Pediatric Epilepsy Surgery

Stereoelectroencephalography (SEEG) is an invasive technique used during the surgical management of medically refractory epilepsy. The utility of SEEG rests in its ability to survey the three-dimensional organization of the epileptogenic zone as well as nearby eloquent cortices. Once concentrated to specialized centers in Europe and Canada, the SEEG methodology has gained worldwide popularity due to its favorable morbidity profile, superior coverage of deep structures, and ability to perform multilobar explorations without the need for craniotomy. This rapid shift in practice represents both a challenge and an opportunity for pediatric neurosurgeons familiar with the subdural grid approach. The purpose of this review is to discuss the indications, technique, and safety of long-term SEEG monitoring in children. In addition to reviewing the conceptual and technical points of the diagnostic evaluation, attention will also be given to SEEG-based interventions (e.g., radiofrequency thermo-coagulation).

Gauging seizure risk

The current paradigm for treatment of epilepsy begins with trials of antiepileptic drugs, followed by evaluation for resective brain surgery in drug-resistant patients. If surgery is not possible or fails to control seizures, some patients benefit from implanted neurostimulation devices. In addition to their therapeutic benefit, some of these devices have diagnostic capability enabling recordings of brain activity with unprecedented chronicity. Two recent studies using different devices for chronic EEG (i.e., over months to years) yielded convergent findings of daily and multiday cycles of brain activity that help explain seizure timing. Knowledge of these patient-specific cycles can be leveraged to gauge and forecast seizure risk, empowering patients to adopt risk-stratified treatment strategies and behavioral modifications. We review evidence that epilepsy is a cyclical disorder, and we argue that implanted monitoring devices should be offered earlier in the treatment paradigm. Chronic EEG would allow pharmacologic treatments tailored to days of high seizure risk-here termed chronotherapy-and would help characterize long timescale seizure dynamics to improve subsequent surgical planning. Coupled with neuromodulation, the proposed approach could improve quality of life for patients and decrease the number ultimately requiring resective surgery. We outline challenges for chronic monitoring and seizure forecasting that demand close collaboration among engineers, neurosurgeons, and neurologists.

The current place of epilepsy surgery

PURPOSE OF REVIEW

Three randomized controlled trials demonstrate that surgical treatment is safe and effective for drug-resistant epilepsy (DRE), yet fewer than 1% of patients are referred for surgery. This is a review of recent trends in surgical referral for DRE, and advances in the field. Reasons for continued underutilization are discussed.

RECENT FINDINGS

Recent series indicate no increase in surgical referral for DRE over the past two decades. One study suggests that decreased referrals to major epilepsy centers can be accounted for by increased referrals to low-volume nonacademic hospitals where results are poorer, and complication rates higher. The increasing ability of high-resolution MRI to identify small neocortical lesions and an increase in pediatric surgeries, in part, explain a relative greater decrease in temporal lobe surgeries. Misconceptions continue to restrict referral. Consequently, advocacy for referral of all patients with DRE to epilepsy centers that offer specialized diagnosis and other alternative treatments, as well as psychosocial support, is recommended. Recent advances will continue to improve the safety and efficacy of surgical treatment and expand the types of patients who benefit from surgical intervention.

SUMMARY

Surgical treatment for epilepsy remains underutilized, in part because of persistent misconceptions. Rather than promote referral for surgery, it would be more appropriate to advocate that all patients with DRE deserve a consultation at a full-service epilepsy center that offers many options for eliminating or reducing disability.