Implantation of Stereoelectroencephalography Electrodes

A Multivariate Approach to Quantifying Risk Factors Impacting Stereotactic Robotic-Guided Stereoelectroencephalography

BACKGROUND AND OBJECTIVES

Stereoelectroencephalography (SEEG) is an important method for invasive monitoring to establish surgical candidacy in approximately half of refractory epilepsy patients. Identifying factors affecting lead placement can mitigate potential surgical risks. This study applies multivariate analyses to identify perioperative factors affecting stereotactic electrode placement.

METHODS

We collected registration and accuracy data for consecutive patients undergoing SEEG implantation between May 2022 and November 2023. Stereotactic robotic guidance, using intraoperative imaging and a novel frame-based fiducial, was used for planning and SEEG implantation. Entry-point (EE), target-point (TE), and angular errors were measured, and statistical univariate and multivariate linear regression analyses were performed.

RESULTS

Twenty-seven refractory epilepsy patients (aged 15-57 years) undergoing SEEG were reviewed. Sixteen patients had unilateral implantation (10 left-sided, 6 right-sided); 11 patients underwent bilateral implantation. The mean number of electrodes per patient was 18 (SD = 3) with an average registration mean error of 0.768 mm (SD = 0.108). Overall, 486 electrodes were reviewed. Univariate analysis showed significant correlations of lead error with skull thickness (EE: P = .003; TE: P = .012); entry angle (EE: P < .001; TE: P < .001; angular error: P = .030); lead length (TE: P = .020); and order of electrode implantation (EE: P = .003; TE: P = .001). Three multiple linear regression models were used. All models featured predictors of implantation region (157 temporal, 241 frontal, 79 parietal, 9 occipital); skull thickness (mean = 5.80 mm, SD = 2.97 mm); order (range: 1-23); and entry angle in degrees (mean = 75.47, SD = 11.66). EE and TE error models additionally incorporated lead length (mean = 44.08 mm, SD = 13.90 mm) as a predictor. Implantation region and entry angle were significant predictors of error (P ≤ .05).

CONCLUSION

Our study identified 2 primary predictors of SEEG lead error, region of implantation and entry angle, with nonsignificant contributions from lead length or order of electrode placement. Future considerations for SEEG may consider varying regional approaches and angles for more optimal accuracy in lead placement.

Vasogenic oedema during stereoelectroencephalography: intracranial pattern and late-onset clinical repercussion

In patients suffering from focal drug-resistant epilepsy, intracranial explorations are the gold standard for identifying the epileptogenic zone and evaluating the possibility of a surgical resection. Amongst them, stereoelectroencephalography (SEEG), using depth electrodes, is a safe procedure. However, complications occur on average in 2% of cases, notably haemorrhages or infections. Vasogenic cerebral oedema constitutes a rarely reported complication. Amongst the 85 patients explored with SEEG between January 2017 and September 2023, three had a clinically and electrophysiologically relevant vasogenic cerebral oedema. In these three patients, the surgical procedure was uneventful. In all three as well, electrodes exploring areas away from the epileptogenic zone recorded some unexpected focal delta slowing with clinically asymptomatic superimposed discharges, a pattern so far only reported in cases of bleeding. Moreover, one patient experienced confusion 10 days after explantation. Post-explantation magnetic resonance imaging showed, in all three patients, a vasogenic oedema that fully resolved a few months later. We did not identify any contributing factors, and there were no particularities concerning the number of electrodes, their implantation site or the recording duration. Focal delta slowing and rhythmic discharges during SEEG can indicate a vasogenic oedema. Clinical consequences can occur after explantation. Evolution is favourable but this misleading pattern must be identified.

The Value of SINO Robot and Angio Render Technology for Stereoelectroencephalography Electrode Implantation in Drug-Resistant Epilepsy

BACKGROUND

 Stereoelectroencephalography (SEEG) electrodes are implanted using a variety of stereotactic technologies to treat refractory epilepsy. The value of the SINO robot for SEEG electrode implantation is not yet defined. The aim of the current study was to assess the value of the SINO robot in conjunction with Angio Render technology for SEEG electrode implantation and to assess its efficacy.

METHODS

 Between June 2018 and October 2020, 58 patients underwent SEEG electrode implantation to resect or ablate their epileptogenic zone (EZ). The SINO robot and the Angio Render technology was used to guide the electrodes and visualize the individual vasculature in a three-dimensional (3D) fashion. The 3D view functionality was used to increase the safety and accuracy of the electrode implantation, and for reducing the risk of hemorrhage by avoiding blood vessels.

RESULTS

 In this study, 634 SEEG electrodes were implanted in 58 patients, with a mean of 10.92 (range: 5-18) leads per patient. The mean entry point localization error (EPLE) was 0.94 ± 0.23 mm (range: 0.39-1.63 mm), and the mean target point localization error (TPLE) was 1.49 ± 0.37 mm (range: 0.80-2.78 mm). The mean operating time per lead (MOTPL) was 6. 18 ± 1.80 minutes (range: 3.02-14.61 minutes). The mean depth of electrodes was 56.96 ± 3.62 mm (range: 27.23-124.85 mm). At a follow-up of at least 1 year, in total, 81.57% (47/58) patients achieved an Engel class I seizure freedom. There were two patients with asymptomatic intracerebral hematomas following SEEG electrode placement, with no late complications or mortality in this cohort.

CONCLUSIONS

 The SINO robot in conjunction with Angio Render technology-in SEEG electrode implantation is safe and accurate in mitigating the risk of intracranial hemorrhage in patients suffering from drug-resistant epilepsy.

The United States Stereotactic EEG Survey: Current Practice and Future Opportunities

PURPOSE

Stereotactic EEG (SEEG) is being increasingly used in the intracranial evaluation of refractory epilepsy in the United States. A 2022 survey of SEEG practices among National Association of Epilepsy Centers tertiary referral (NAEC level IV) centers found largely similar practices across institutions. However, a few significant differences were noted in technical and patient care practice, and in the level of SEEG background training. In the year since publication, we review the identified challenges facing SEEG practice and suggest specific corrective action.

CONCLUSIONS

Stereotactic EEG has rapidly become the principal method for intracranial EEG monitoring in epilepsy surgery centers in the United States. The rate of adoption of SEEG is currently higher than the growth of invasive monitoring overall. Most report similar indications for SEEG, although significant variability exists in personnel expertise and technical and patient care practice. Consensus statements, guidelines, and review of postgraduate training curricula are urgently needed to benchmark SEEG practice and develop appropriate skillsets in the next generation of practitioners in the United States.

NeuroDots: From Single-Target to Brain-Network Modulation: Why and What Is Needed?

OBJECTIVES

Current techniques in brain stimulation are still largely based on a phrenologic approach that a single brain target can treat a brain disorder. Nevertheless, meta-analyses of brain implants indicate an overall success rate of 50% improvement in 50% of patients, irrespective of the brain-related disorder. Thus, there is still a large margin for improvement. The goal of this manuscript is to 1) develop a general theoretical framework of brain functioning that is amenable to surgical neuromodulation, and 2) describe the engineering requirements of the next generation of implantable brain stimulators that follow from this theoretic model.

MATERIALS AND METHODS

A neuroscience and engineering literature review was performed to develop a universal theoretical model of brain functioning and dysfunctioning amenable to surgical neuromodulation.

RESULTS

Even though a single target can modulate an entire network, research in network science reveals that many brain disorders are the consequence of maladaptive interactions among multiple networks rather than a single network. Consequently, targeting the main connector hubs of those multiple interacting networks involved in a brain disorder is theoretically more beneficial. We, thus, envision next-generation network implants that will rely on distributed, multisite neuromodulation targeting correlated and anticorrelated interacting brain networks, juxtaposing alternative implant configurations, and finally providing solid recommendations for the realization of such implants. In doing so, this study pinpoints the potential shortcomings of other similar efforts in the field, which somehow fall short of the requirements.

CONCLUSION

The concept of network stimulation holds great promise as a universal approach for treating neurologic and psychiatric disorders.

The value of additional electrodes when stereo-electroencephalography is inconclusive

OBJECTIVE

Stereo-electroencephalography (SEEG) is the preferred method for intracranial localization of the seizure-onset zone (SOZ) in drug-resistant focal epilepsy. Occasionally SEEG evaluation fails to confirm the pre-implantation hypothesis. This leads to a decision tree regarding whether the addition of SEEG electrodes (two-step SEEG - 2sSEEG) or placement of subdural electrodes (SDEs) after SEEG (SEEG2SDE) would help. There is a dearth of literature encompassing this scenario, and here we aimed to characterize outcomes following unplanned two-step intracranial EEG (iEEG).

METHODS

All 225 adult SEEG cases over 8 years at our institution were reviewed to extract patient data and outcomes following a two-step evaluation. Three raters independently quantified benefits of additional intracranial electrodes. The relationship between two-step iEEG benefit and clinical outcome was then analyzed.

RESULTS

Fourteen patients underwent 2sSEEG and nine underwent SEEG2SDE. In the former cohort, the second SEEG procedure was performed for these reasons-precise localization of the SOZ (36%); defining margins of eloquent cortex (21%); and broadening coverage in the setting of non-localizable seizure onsets (43% of cases). Sixty-four percent of 2sSEEG cases were consistently deemed beneficial (Light's κ = 0.80). 2sSEEG performed for the first two indications was much more beneficial than when onsets were not localizable (100% vs 17%, p = .02). In the SEEG2SDE cohort, SDEs identified the SOZ and enabled delineation of margins relative to eloquent cortex in all cases.

SIGNIFICANCE

The two-step iEEG is useful if the initial evaluation is broadly concordant with the original electroclinical hypothesis, where it can clarify onset zones or delineate safe surgical margins; however, it provides minimal benefit when the implantation hypothesis is erroneous, and we recommend that 2sSEEG not be generally utilized in such cases. SDE implantation after SEEG minimizes the need for SDEs and is helpful in delineating surgical boundaries relative to ictal-onset zones and eloquent cortex.

Frame-based versus robot-assisted stereo-electro-encephalography for drug-resistant epilepsy

BACKGROUND

Stereoelectroencephalography (SEEG) is an effective presurgical invasive evaluation for drug-resistant epilepsies. The introduction of robotic devices provides a simplified, accurate, and safe alternative to the conventional SEEG technique. We report our institutional experience with robot-assisted SEEG and compare its in vivo accuracy, operation efficiency, and safety with the more traditional SEEG workflow.

METHODS

All patients with medically refractory focal epilepsy who underwent SEEG depth electrode implantation between 2014 and 2022 were included in this study. Technical advancements of the robot-assisted technique are described. Analyses of patient demographics, electrode implantation accuracy, operation time, and procedure-related complications were performed.

RESULTS

One hundred and sixty-six patients underwent 167 SEEG procedures. The first 141 procedures were performed using a conventional approach involving a Leksell stereotactic system, and the last 26 procedures were robot-assisted. Among the 1726 depth electrodes that were inserted, the median entry point localization error was as follows: conventional (1.0 mm; range, 0.1-33.5 mm) and robot-assisted (1.1 mm; range, 0-4.8 mm) (P = 0.17). The median target point localization error was as follows: conventional (2.8 mm; range, 0.1-49 mm) and robot-assisted (1.8 mm; range, 0-30.3 mm) (P < 0.001). The median operation time was significantly reduced with the robot-assisted workflow (90 min vs. 77.5 min; P < 0.01). Total complication rates were as follows: conventional (17.7%) and robot-assisted (11.5%) (P = 0.57). Major complication rates were 3.5% and 7.7% (P = 0.77), respectively.

CONCLUSIONS

SEEG is a safe and highly accurate method that provides essential guidance for epilepsy surgery. Implementing SEEG in conjunction with multimodal planning systems and robotic devices can further increase safety margin, surgical efficiency, and accuracy.

Safety, Accuracy, and Efficacy of Robot-Assisted Stereo Electroencephalography in Children of Different Ages

BACKGROUND AND OBJECTIVES

Aimed to investigate the safety, accuracy, and efficacy of stereo electroencephalography (SEEG) in children of various ages, with particular emphasis on those younger than 3 years. There is limited guidance regarding whether SEEG can conducted on very young children.

METHODS

This retrospective study was conducted between July 2018 and August 2022. It involved 88 patients who underwent 99 robot-assisted SEEG procedures at our center. The patients were categorized into 3 groups based on their age at the time of the robot-assisted SEEG procedures: group 1 (3 years and younger, n = 28), group 2 (age 3-6 years, n = 27), and group 3 (older than 6 years, n = 44). Clinical data, SEEG demographics, complications, and seizure outcomes were analyzed.

RESULTS

A total of 675 electrodes were implanted, with an average of 6.82 ± 3.47 (2.00-16.00) electrodes per patient (P = .052). The average target point error for the 675 electrodes was 1.93 ± 1.11 mm, and the average entry point error was 1.30 ± 0.97 mm (P = .536 and P = .549, respectively). The overall percentage of complications was 6.06% (P = .879). No severe or long-term neurologic impairment was observed. Of the total 99 procedures included in this study, 78 were admitted for epilepsy surgery for the first time, while 9 patients were treated twice and 1 patient was treated 3 times. There were 21 radiofrequency thermocoagulation and 78 second-stage resective procedures performed after SEEG. There was no statistically significant difference in Engel class I outcomes among the patients who underwent SEEG in the 3 age groups (P = .621).

CONCLUSION

Robot-assisted SEEG were demonstrated to be safe, accurate, and efficient across different age groups of children. This technique is suitable for children younger than 3 years who have indications for SEEG placement.

Seizure Control Outcomes following Resection of Cortical Dysplasia in Patients with DEPDC5 Variants: A Systematic Review and Individual Patient Data Analysis

There is insufficient evidence regarding the efficacy of epilepsy surgery in patients with pharmacoresistant focal epilepsy and coexistent DEPDC5 (dishevelled EGL-10 and pleckstrin domain-containing protein 5) pathogenic (P), likely pathogenic (LP), or variance of unknown significance (VUS) variants. To conduct a systematic review on the literature regarding the use and efficacy of epilepsy surgery as an intervention for patients with DEPDC5 variants who have pharmacoresistant epilepsy. A systematic review of the current literature published regarding the outcomes of epilepsy surgery for patients with DEPDC5 variants was conducted. Demographics and individual patient data were recorded and analyzed. Subsequent statistical analysis was performed to assess significance of the findings. A total of eight articles comprising 44 DEPDC5 patients with genetic variants undergoing surgery were included in this study. The articles primarily originated in high-income countries (5/8, 62.5%). The average age of the subjects was 10.06 ± 9.41 years old at the time of study. The most common form of epilepsy surgery was focal resection (38/44, 86.4%). Thirty-seven of the 40 patients (37/40, 92.5%) with reported seizure frequency results had improvement. Twenty-nine out of 38 patients (29/38, 78.4%) undergoing focal resection achieved Engel Score I postoperatively, and two out of four patients achieved International League Against Epilepsy I (50%). Epilepsy surgery is effective in patients with pharmacoresistant focal epilepsy and coexistent DEPDC5 P, LP, or VUS variants.

Frameless robot-assisted stereoelectroencephalography-guided radiofrequency: methodology, results, complications and stereotactic application accuracy in pediatric hypothalamic hamartomas

Objective

We aimed to investigate the methodology, results, complications and stereotactic application accuracy of electrode implantation and its explanatory variables in stereoelectroencephalography-guided radiofrequency thermocoagulation (SEEG-RFTC) for pediatric hypothalamic hamartoma.

Methods

Children with hypothalamic hamartoma who underwent robot-assisted SEEG-RFTC between December 2017 and November 2021 were retrospectively analyzed. The methodology, seizure outcome, complications, in vivo accuracy of electrode implantation and its explanatory variables were analyzed.

Results

A total of 161 electrodes were implanted in 28 patients with 30 surgeries. Nine electrodes not following the planned trajectories due to intraoperative replanning were excluded, and the entry point and target point errors of 152 electrodes were statistically analyzed. The median entry point error was 0.87 mm (interquartile range, 0.50-1.41 mm), and the median target point error was 2.74 mm (interquartile range, 2.01-3.63 mm). Multifactor analysis showed that whether the electrode was bent (b = 2.16, p < 0.001), the length of the intracranial electrode (b = 0.02, p = 0.049), and the entry point error (b = 0.337, p = 0.017) had statistically significant effects on the target error. During follow-up (mean duration 31 months), 27 of 30 (90%) procedures were seizure-free. The implantation-related complication rate was 2.6% (4/152), and the major complication rate in all procedures was 6.7% (2/30).

Conclusion

Robot-assisted SEEG-RFTC is a safe, effective and accurate procedure for pediatric hypothalamic hamartoma. Explanatory variables significantly associated with the target point localization error at multivariate analysis include whether the intracranial electrode is bent, the intracranial electrode length and the entry point error.

Localizing epileptogenic zones with high-frequency oscillations and directed connectivity

PURPOSE

Precise localization of the epileptogenic zone (EZ) is essential for epilepsy surgery. Existing methods often fail to detect slow onset patterns or similar neural activities presented in the recorded signals. To address this issue, we propose a new measure to quantify epileptogenicity, i.e., the connectivity high-frequency epileptogenicity index (cHFEI).

METHODS

The cHFEI method combines directed connectivity and high-frequency oscillations (HFOs) to measure the epileptogenicity of regions involved in a brain network. By applying this method to stereoelectroencephalography (SEEG) recordings of 49 seizures in 20 patients, we calculated the accuracy, sensitivity, and precision with a visually identified epileptogenic zone as a reference. The performance was evaluated by the confusion matrix and the area under the receiver operating characteristic (ROC) curve.

RESULTS

Epileptic network estimation based on cHFEI successfully distinguished brain regions involved in seizure onset from the propagation network. Moreover, cHFEI outperformed other existing detection methods in the estimation of EZs in all patients, with an average area under the ROC curve of 0.88 and an accuracy of 0.85.

CONCLUSIONS

cHFEI can characterize EZ in a robust manner despite various seizure onset patterns and has potential application in epilepsy therapy.

Robotic-Assisted Stereoelectroencephalography: A Systematic Review and Meta-Analysis of Safety, Outcomes, and Precision in Refractory Epilepsy Patients

Robotic assistance in stereoelectroencephalography (SEEG) holds promising potential for enhancing accuracy, efficiency, and safety during electrode placement and surgical procedures. This systematic review and meta-analysis, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and International Prospective Register of Systematic Reviews (PROSPERO) registration, delves into the latest advancements and implications of robotic systems in SEEG, while meticulously evaluating outcomes and safety measures. Among 855 patients suffering from medication-refractory epilepsy who underwent SEEG in 29 studies, averaging 24.6 years in age, the most prevalent robots employed were robotic surgical assistant (ROSA) (450 patients), Neuromate (207), Sinovation (140), and ISys1 (58). A total of 8,184 electrodes were successfully implanted, with an average operative time of 157.2 minutes per procedure and 15.1 minutes per electrode, resulting in an overall mean operative time of 157.7 minutes across all studies. Notably, the mean target point error (TPE) stood at 2.13 mm, the mean entry point error (EPE) at 1.48 mm, and postoperative complications occurred in 7.69% of robotically assisted (RA) SEEG cases (60), with 85% of these complications being asymptomatic. This comprehensive analysis underscores the safety and efficacy of RA-SEEG in patients with medication-refractory epilepsy, characterized by low complication rates, reduced operative time, and precise electrode placement, supporting its widespread adoption in clinical practice, with no discernible differences noted among the various robotic systems.

Stereo-EEG tailored resection in a child with presumed perinatal post-stroke epilepsy: The complex organization of epileptogenic zone

Introduction

Only a few studies have focused on tailored resection in post-stroke epilepsy, in which hemispherectomy and hemispherotomy are the most recognized treatments.

Case description

We describe the case of a patient with drug-resistant, presumed perinatal, post-stroke epilepsy and moderate right hemiparesis. The seizures were stereotyped, both spontaneous and induced by sudden noises and somatosensory stimuli. Considering the discordant anatomic-electro-clinical data - left perisylvian malacic lesion with electrical onset over the left mesial fronto-central leads - and the patient's functional preservation, SEEG was performed. SEEG revealed sub-continuous abnormalities in the perilesional regions. Several seizures were recorded, with onset over the premotor area, rapidly involving the motor and insular-opercular regions. We decided for a combined surgical approach, SEEG-guided radiofrequency thermocoagulation, on the fronto-mesial structure but also on the central operculum, followed by resective surgery including only the fronto-mesial structures.

Discussion and conclusion

The SEEG allowed to localize the epileptogenic zone far away from the anatomical lesion but connected to part of it. A combined surgical approach tailored on SEEG results allowed a good outcome (Engel Ib) without additional deficits.

Automated Identification of Stereoelectroencephalography Contacts and Measurement of Factors Influencing Accuracy of Frame Stereotaxy

OBJECTIVE

Stereoelectroencephalography (SEEG) is an established invasive diagnostic technique for use in patients with drug-resistant focal epilepsy evaluated before resective epilepsy surgery. The factors that influence the accuracy of electrode implantation are not fully understood. Adequate accuracy prevents the risk of major surgery complications. Precise knowledge of the anatomical positions of individual electrode contacts is crucial for the interpretation of SEEG recordings and subsequent surgery.

METHODS

We developed an image processing pipeline to localize implanted electrodes and detect individual contact positions using computed tomography (CT), as a substitute for time-consuming manual labeling. The algorithm automates measurement of parameters of the electrodes implanted in the skull (bone thickness, implantation angle and depth) for use in modeling of predictive factors that influence implantation accuracy.

RESULTS

Fifty-four patients evaluated by SEEG were analyzed. A total of 662 SEEG electrodes with 8,745 contacts were stereotactically inserted. The automated detector localized all contacts with better accuracy than manual labeling (p < 0.001). The retrospective implantation accuracy of the target point was 2.4 ± 1.1 mm. A multifactorial analysis determined that almost 58% of the total error was attributable to measurable factors. The remaining 42% was attributable to random error.

CONCLUSION

SEEG contacts can be reliably marked by our proposed method. The trajectory of electrodes can be parametrically analyzed to predict and validate implantation accuracy using a multifactorial model.

SIGNIFICANCE

This novel, automated image processing technique is a potentially clinically important, assistive tool for increasing the yield, efficiency, and safety of SEEG.

Intraparenchymal and Subarachnoid Hemorrhage in Stereotactic Electroencephalography Caused by Indirect Adjacent Arterial Injury: Illustrative Case

The complication rate of stereotactic electroencephalography (SEEG) is generally low, but various types of postoperative hemorrhage have been reported. We presented an unusual hemorrhagic complication after SEEG placement. A 20-year-old man presented with suspected frontal lobe epilepsy. We implanted 11 SEEG electrodes in the bilateral frontal lobes and the left insula. Computed tomography after implantation showed intraparenchymal hemorrhage in the left temporal lobe and insula and subarachnoid hemorrhage in the left Sylvian cistern. Later, the point of vessel injury was revealed from the identification of a pseudoaneurysm, but this location was not along the planned or actual electrode trajectory. The cause of hemorrhage was suggested to be indirect injury from stretching of the arachnoid trabeculae by the puncture needle.

A Method of Intraoperative Registration Verification to Prevent Accuracy Errors in Robot-Assisted Stereotactic Electroencephalography Electrode Placement

BACKGROUND

Robotic-assisted stereotactic electroencephalography (sEEG) electrode placement is increasingly common at specialized epilepsy centers. High accuracy and low complication rates are essential to realizing the benefits of sEEG surgery. The aim of this study was to describe for the first time in the literature a method for a stereotactic registration checkpoint to verify intraoperative accuracy during robotic-assisted sEEG and to report our institutional experience with this technique.

METHODS

All cases performed with this technique since the adoption of robotic-assisted sEEG at our institution were retrospectively reviewed.

RESULTS

In 4 of 111 consecutive sEEG operations, use of the checkpoint detected an intraoperative registration error, which was addressed before completion of sEEG electrode placement.

CONCLUSIONS

The use of a registration checkpoint in robotic-assisted sEEG surgery is a simple technique that can prevent electrode misplacement and improve the safety profile of this procedure.

Amortized Bayesian inference on generative dynamical network models of epilepsy using deep neural density estimators

Whole-brain modeling of epilepsy combines personalized anatomical data with dynamical models of abnormal activities to generate spatio-temporal seizure patterns as observed in brain imaging data. Such a parametric simulator is equipped with a stochastic generative process, which itself provides the basis for inference and prediction of the local and global brain dynamics affected by disorders. However, the calculation of likelihood function at whole-brain scale is often intractable. Thus, likelihood-free algorithms are required to efficiently estimate the parameters pertaining to the hypothetical areas, ideally including the uncertainty. In this study, we introduce the simulation-based inference for the virtual epileptic patient model (SBI-VEP), enabling us to amortize the approximate posterior of the generative process from a low-dimensional representation of whole-brain epileptic patterns. The state-of-the-art deep learning algorithms for conditional density estimation are used to readily retrieve the statistical relationships between parameters and observations through a sequence of invertible transformations. We show that the SBI-VEP is able to efficiently estimate the posterior distribution of parameters linked to the extent of the epileptogenic and propagation zones from sparse intracranial electroencephalography recordings. The presented Bayesian methodology can deal with non-linear latent dynamics and parameter degeneracy, paving the way for fast and reliable inference on brain disorders from neuroimaging modalities.

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.

Clinical Impacts of Stereotactic Electroencephalography on Epilepsy Surgery and Associated Issues in the Current Situation in Japan

Stereotactic electroencephalography (SEEG) is receiving increasing attention as a safe and effective technique in the invasive evaluation for epileptogenic zone (EZ) detection. The main clinical question is whether the use of SEEG truly improves outcomes. Herein, we compared outcomes in our patients after three types of intracranial EEG (iEEG): SEEG, the subdural electrode (SDE), and a combined method using depth and strip electrodes. We present here our preliminary results from two demonstrative cases. Several international reports from large epilepsy centers found the following clinical advantages of SEEG: 1) three-dimensional analysis of structures, including bilateral and multilobar structures; 2) low rate of complications; 3) less pneumoencephalopathy and less patient burden during postoperative course, which allows the initiation of video-EEG monitoring immediately after implantation and does not require resection to be performed in the same hospitalization; and 4) a higher rate of good seizure control after resection. In other words, SEEG more accurately identified the EZ than the SDE method. We obtained similar results in our preliminary experiences under limited conditions. In Japan, as of August 2022, dedicated electrodes and SEEG accessories have not been approved and the use of the robot arm is not widespread. The Japanese medical community is hopeful that these issues will soon be resolved and that the experience with SEEG in Japan will align with that of large epilepsy centers internationally.

Source localization of ictal SEEG to predict postoperative seizure outcome

OBJECTIVE

Stereo-electroencephalography (SEEG) is inherently-three-dimensional and can be modeled using source localization. This study aimed to assess the validity of ictal SEEG source localization.

METHODS

The dominant frequency at ictal onset was used for source localization in the time and frequency domains using rotating dipoles and current density maps. Validity was assessed by concordance with the epileptologist-defined seizure onset zone (conventional SOZ) and the surgical treatment volume (TV) of seizure-free versus non-seizure-free patients.

RESULTS

Source localization was performed on 68 seizures from 27 patients. Median distance to nearest contact in the conventional SOZ was 7 (IQR 6-12) mm for time-domain dipoles. Current density predicted ictal activity with up to 86 % (60-87 %) accuracy. Distance from time-domain dipoles to the TV was smaller (P = 0.045) in seizure-free (2 [0-4] mm) versus non-seizure-free (12 [2-17] mm) patients, and predicted surgical outcome with 91 % sensitivity and 63 % specificity. Removing near-field data from contacts within the TV negated outcome prediction (P = 0.51).

CONCLUSIONS

Source localization of SEEG accurately mapped ictal onset compared with conventional interpretation. Proximity of dipoles to the TV predicted seizure outcome when near-field recordings were analyzed.

SIGNIFICANCE

Ictal SEEG source localization is useful in corroborating the epileptogenic zone, assuming near-field recordings are obtained.

Does Stereoelectroencephalography Add Value in Patients with Lesional Epilepsy?

OBJECTIVE

Stereoelectroencephalography (SEEG) has gained popularity as an invasive monitoring modality for epileptogenic zone (EZ) localization. The need and indications for SEEG in patients with evident brain lesions or associated abnormalities on imaging is debated. We report our experience with SEEG as a presurgical evaluation tool for patients with lesional epilepsy.

METHODS

A retrospective cohort study was performed of 131 patients with lesional or magnetic resonance imaging abnormality-associated medically refractory focal epilepsy who underwent resections from 2010 to 2017. Seventy-one patients had SEEG followed by resection, and 60 had no invasive recordings. Volumetric analysis of resection cavities from 3T magnetic resonance imaging was performed.

RESULTS

Mean lesion and resection volumes for SEEG and non-SEEG were 16.2 (standard deviation [SD] = 29) versus 23.7 cm3 (SD = 38.4) and 28.1 (SD = 23.2) versus 43.6 cm3 (SD = 43.5), respectively (P = 0.009). Comparing patients with seizure recurrence and patients who remained seizure free, significantly associated variables with seizure recurrence included mean number of failed antiseizure medications (6.86 [SD = 0.32] vs. 5.75 [SD = 0.32]; P = 0.01) and in SEEG patients the mean number of electrodes implanted (8.1 [SD = 0.8] vs. 5.0 [SD = 0.8]; P = 0.005). After multivariate analysis, only failed numbers of medication remained significantly associated with seizure recurrence.

CONCLUSIONS

Seizure outcomes did not correlate with final resection volume after SEEG evaluation. SEEG evaluation presurgically can be used to maintain the efficacy of resection and decrease the volume and subsequent risk of extensive tissue removal. We believe that this technology allows resective surgery to proceed in a subpopulation of patients with lesional epilepsy who may otherwise not have been considered surgical candidates.

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.

Stereoelectroencephalography before 2 years of age

OBJECTIVE

Stereoelectroencephalography (SEEG) is a widely used technique for localizing seizure onset zones prior to resection. However, its use has traditionally been avoided in children under 2 years of age because of concerns regarding pin fixation in the immature skull, intraoperative and postoperative electrode bolt security, and stereotactic registration accuracy. In this retrospective study, the authors describe their experience using SEEG in patients younger than 2 years of age, with a focus on the procedure’s safety, feasibility, and accuracy as well as surgical outcomes.

METHODS

A retrospective review of children under 2 years of age who had undergone SEEG while at Children’s Hospital of Philadelphia between November 2017 and July 2021 was performed. Data on clinical characteristics, surgical procedure, imaging results, electrode accuracy measurements, and postoperative outcomes were examined.

RESULTS

Five patients younger than 2 years of age underwent SEEG during the study period (median age 20 months, range 17–23 months). The mean age at seizure onset was 9 months. Developmental delay was present in all patients, and epilepsy-associated genetic diagnoses included tuberous sclerosis (n = 1), KAT6B (n = 1), and NPRL3 (n = 1). Cortical lesions included tubers from tuberous sclerosis (n = 1), mesial temporal sclerosis (n = 1), and cortical dysplasia (n = 3). The mean number of placed electrodes was 11 (range 6–20 electrodes). Bilateral electrodes were placed in 1 patient. Seizure onset zones were identified in all cases. There were no SEEG-related complications, including skull fracture, electrode misplacement, hemorrhage, infection, cerebrospinal fluid leakage, electrode pullout, neurological deficit, or death. The mean target point error for all electrodes was 1.0 mm. All patients proceeded to resective surgery, with a mean follow-up of 21 months (range 8–53 months). All patients attained a favorable epilepsy outcome, including Engel class IA (n = 2), IC (n = 1), ID (n = 1), and IIA (n = 1).

CONCLUSIONS

SEEG can be safely, accurately, and effectively utilized in children under age 2 with good postoperative outcomes using standard SEEG equipment. With minimal modification, this procedure is feasible in those with immature skulls and guides the epilepsy team’s decision-making for early and optimal treatment of refractory epilepsy through effective localization of seizure onset zones.

Previous, current, and future stereotactic EEG techniques for localising epileptic foci

INTRODUCTION

Drug-resistant focal epilepsy presents a significant morbidity burden globally, and epilepsy surgery has been shown to be an effective treatment modality. Therefore, accurate identification of the epileptogenic zone for surgery is crucial, and in those with unclear noninvasive data, stereoencephalography is required.

AREAS COVERED

This review covers the history and current practices in the field of intracranial EEG, particularly analyzing how stereotactic image-guidance, robot-assisted navigation, and improved imaging techniques have increased the accuracy, scope, and use of SEEG globally.

EXPERT OPINION

We provide a perspective on the future directions in the field, reviewing improvements in predicting electrode bending, image acquisition, machine learning and artificial intelligence, advances in surgical planning and visualization software and hardware. We also see the development of EEG analysis tools based on machine learning algorithms that are likely to work synergistically with neurophysiology experts and improve the efficiency of EEG and SEEG analysis and 3D visualization. Improving computer-assisted planning to minimize manual input from the surgeon, and seamless integration into an ergonomic and adaptive operating theater, incorporating hybrid microscopes, virtual and augmented reality is likely to be a significant area of improvement in the near future.

Neural decoding of semantic concepts: A systematic literature review

Objective Semantic concepts are coherent entities within our minds. They underpin our thought processes and are a part of the basis for our understanding of the world. Modern neuroscience research is increasingly exploring how individual semantic concepts are encoded within our brains and a number of studies are beginning to reveal key patterns of neural activity that underpin specific concepts. Building upon this basic understanding of the process of semantic neural encoding, neural engineers are beginning to explore tools and methods for semantic decoding: identifying which semantic concepts an individual is focused on at a given moment in time from recordings of their neural activity. In this paper we review the current literature on semantic neural decoding. Approach We conducted this review according to the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) guidelines. Specifically, we assess the eligibility of published peer-reviewed reports via a search of PubMed and Google Scholar. We identify a total of 74 studies in which semantic neural decoding is used to attempt to identify individual semantic concepts from neural activity. Results Our review reveals how modern neuroscientific tools have been developed to allow decoding of individual concepts from a range of neuroimaging modalities. We discuss specific neuroimaging methods, experimental designs, and machine learning pipelines that are employed to aid the decoding of semantic concepts. We quantify the efficacy of semantic decoders by measuring information transfer rates. We also discuss current challenges presented by this research area and present some possible solutions. Finally, we discuss some possible emerging and speculative future directions for this research area. Significance Semantic decoding is a rapidly growing area of research. However, despite its increasingly widespread popularity and use in neuroscientific research this is the first literature review focusing on this topic across neuroimaging modalities and with a focus on quantifying the efficacy of semantic decoders.

Epidural grid, a new methodology of invasive intracranial EEG monitoring: A technical note and experience of a single center

INTRODUCTION

Subdural grid monitoring (SDG) has the advantage to provide continuous coverage over a larger area of cortex, direct visualization of electrode location and functional mapping. However, SDG can cause direct irritation of the cortex or postoperative headaches due to cerebrospinal fluid (CSF) leakage. Epidural grid monitoring (EDG) without opening the dura is thought to reduce the possibility of these complications. We report our experience with EDG.

METHODS

We described our surgical technique of EDG in invasive intracranial electroencephalography (iEEG) monitoring. A retrospective review of 30 patients who underwent grid placement of iEEG between March 2019 and December 2020 was performed to compare SDG and EDG.

RESULTS

Of the 30 patients, 10 patients underwent SDG and 20 patients underwent EDG. There was no difference in age between SDG and EDG groups (p = 0.13). Also, there was no difference in the number of grid electrodes, craniotomy size, number of electrodes per craniotomy area and postoperative complication rate (p = 0.32, 0.84, 0.58 and 0.40). However, the maximum number of electrodes that have been undermined from the bone margin was much higher in SDG group (SDG 4.6 ± 2.2 vs. EDG 2.0 ± 0.9; p = 0.001). The demand for postoperative analgesics was significantly lower in EDG group (SDG 13.4 ± 9.1 vs. EDG 4.1 ± 4.3; p = 0.012); and the demand for postoperative antiemetics also tended to be low (SDG 4.6 ± 3.6 vs. EDG 1.8 ± 1.6; p = 0.078).

CONCLUSIONS

There was no significant difference in craniotomy and electrode insertion between the two groups; however, the EDG group showed less postoperative headache and nausea. Though not in direct contact with the cortex, the quality of the electrophysiological signal received through the electrode in EDG is comparable to that of the SDG. The EDG enables to detect the onset of seizure and delineate the epileptogenic zone sufficiently. Moreover, functional mapping is possible with EDG. Therefore, EDG has the sufficient potential to replace SDG for monitoring of the lateral surface of brain.

SEEG in 3D: Interictal Source Localization From Intracerebral Recordings

BACKGROUND

Stereo-electroencephalography (SEEG) uses a three-dimensional configuration of depth electrodes to localize epileptiform activity, but traditional analysis of SEEG is spatially restricted to the point locations of the electrode contacts. Interpolation of brain activity between contacts might allow for three-dimensional representation of epileptiform activity and avoid pitfalls of SEEG interpretation.

OBJECTIVE

The goal of this study was to validate SEEG-based interictal source localization and assess the ability of this technique to monitor far-field activity in non-implanted brain regions.

METHODS

Interictal epileptiform discharges were identified on SEEG in 26 patients who underwent resection, ablation, or disconnection of the suspected epileptogenic zone. Dipoles without (free) and with (scan) gray matter restriction, and current density (sLORETA and SWARM methods), were calculated using a finite element head model. Source localization results were compared to the conventional irritative zone (IZ) and the surgical treatment volumes (TV) of seizure-free vs. non-seizure-free patients.

RESULTS

The median distance from dipole solutions to the nearest contact in the conventional IZ was 7 mm (interquartile range 4-15 mm for free dipoles and 4-14 mm for scan dipoles). The IZ modeled with SWARM predicted contacts within the conventional IZ with 83% (75-100%) sensitivity and 94% (88-100%) specificity. The proportion of current within the TV was greater in seizure-free patients (P = 0.04) and predicted surgical outcome with 45% sensitivity and 93% specificity. Dipole solutions and sLORETA results did not correlate with seizure outcome. Addition of scalp EEG led to more superficial modeled sources (P = 0.03) and negated the ability to predict seizure outcome (P = 0.23). Removal of near-field data from contacts within the TV resulted in smearing of the current distribution (P = 0.007) and precluded prediction of seizure freedom (P = 0.20).

CONCLUSIONS

Source localization accurately represented interictal discharges from SEEG. The proportion of current within the TV distinguished between seizure-free and non-seizure-free patients when near-field recordings were obtained from the surgical target. The high prevalence of deep sources in this cohort likely obscured any benefit of concurrent scalp EEG. SEEG-based interictal source localization is useful in illustrating and corroborating the epileptogenic zone. Additional techniques are needed to localize far-field epileptiform activity from non-implanted brain regions.

Stereoelectroencephalography in the very young: Case report

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To the best of our knowledge this is the youngest reported patient implanted with SEEG.

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Accurate and safe SEEG surgery may be feasible in patients as young as 17 months-old.

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Robotic SEEG with standard tools may be effectively used in this very young population.

Stereoelectroencephalography (SEEG) is an increasingly popular invasive monitoring approach to epilepsy surgery in patients with drug-resistant epilepsies. The technique allows a three-dimensional definition of the epileptogenic zones (EZ) in the brain. It has been shown to be safe and effective in adults and older children but has been used sparingly in children less than two years old due to concerns about pin fixation in thin bone, registration accuracy, and bolt security. As such, most current series of pediatric invasive EEG explorations do not include young participants, and, when they do, SEEG is often not utilized for these patients. Recent national survey data further suggests SEEG is infrequently utilized in very young patients. We present a novel case of SEEG used to localize the EZ in a 17-month-old patient with thin cranial bone, an open fontanelle, and severe drug-resistant epilepsy due to tuberous sclerosis complex (TSC), with excellent accuracy, surgical results, and seizure remission.

The Sensitivity of Scalp EEG at Detecting Seizures-A Simultaneous Scalp and Stereo EEG Study

PURPOSE

Compare the detection rate of seizures on scalp EEG with simultaneous intracranial stereo EEG (SEEG) recordings.

METHODS

Twenty-seven drug-resistant epilepsy patients undergoing SEEG with simultaneous scalp EEG as part of their surgical work-up were included. A total of 172 seizures were captured.

RESULTS

Of the 172 seizures detected on SEEG, 100 demonstrated scalp ictal patterns. Focal aware and subclinical seizures were less likely to be seen on scalp, with 33% of each observed when compared with focal impaired aware (97%) and focal to bilateral tonic-clonic seizures (100%) (P < 0.001). Of the 72 seizures without ictal scalp correlate, 32 demonstrated an abnormality during the SEEG seizure that was identical to an interictal abnormality. Seizures from patients with MRI lesions were statistically less likely to be seen on scalp than seizures from nonlesional patients (P = 0.0162). Stereo EEG seizures not seen on scalp were shorter in duration (49 seconds) compared with SEEG seizures seen on scalp (108.6 seconds) (P < 0.001).

CONCLUSIONS

Scalp EEG is not a sensitive tool for the detection of focal aware and subclinical seizures but is highly sensitive for the detection of focal impaired aware and focal to bilateral tonic-clonic seizures. Longer duration of seizure and seizures from patients without MRI lesions were more likely to be apparent on scalp. Abnormalities seen interictally may at times represent an underlying seizure. The cognitive, affective, and behavioral long-term effects of ongoing difficult-to-detect seizures are not known.

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.

Variation in pediatric stereoelectroencephalography practice among pediatric neurosurgeons in the United States: survey results

OBJECTIVE

Stereoelectroencephalography (SEEG) has become widespread in the United States during the past decade. Many pediatric neurosurgeons practicing SEEG may not have had experience with this technique during their formal training, and the literature is mostly limited to single-center series. As a result, implementation of this relatively new technique may vary at different institutions. The authors hypothesized that aspects of SEEG experience, techniques, and outcomes would vary widely among programs across the country.

METHODS

An electronic survey with 35 questions addressing the categories of training and experience, technique, electrode locations, and outcomes was sent to 128 pediatric epilepsy surgeons who were potential SEEG users.

RESULTS

Sixty-one pediatric fellowship-trained epilepsy surgeons in the United States responded to the survey. Eighty-nine percent were actively using SEEG in their practice. Seventy-two percent of SEEG programs were in existence for less than 5 years, and 68% were using SEEG for > 70% of their invasive monitoring. Surgeons at higher-volume centers operated on younger patients (p < 0.001). Most surgeons (70%) spent 1-3 hours per case planning electrode trajectories. Two-thirds of respondents reported a median implant duration of 5-7 days, but 16% reported never having an implant duration > 5 days, and 16% reported having had implants stay in place for > 4 weeks. The median response for the median number of electrodes initially implanted was 12 electrodes, although 19% of respondents reported median implants of 5-8 electrodes and 17% reported median implants of 15-18 electrodes. Having a higher volume of SEEG cases per year was associated with a higher median number of electrodes implanted (p < 0.001). Most surgeons found SEEG helpful in defining an epileptic network and reported that most of their SEEG patients undergo focal surgical treatment.

CONCLUSIONS

SEEG has been embraced by the pediatric epilepsy surgery community. Higher case volume is correlated with a tendency to place more electrodes and operate on younger patients. For most parameters addressed in the survey, responses from surgeons clustered around a norm, though additional findings of substantial variations highlight differences in implementation and philosophy among pediatric epilepsy programs.

Oblique trajectory angles in robotic stereo-electroencephalography

OBJECTIVE

Traditional stereo-electroencephalography (sEEG) entails the use of orthogonal trajectories guided by seizure semiology and arteriography. Advances in robotic stereotaxy and computerized neuronavigation have made oblique trajectories more feasible and easier to implement without formal arteriography. Such trajectories provide access to components of seizure networks not readily sampled using orthogonal trajectories. However, the dogma regarding the relative safety and predictability of orthogonal and azimuth-based trajectories persists, given the absence of data regarding the safety and efficacy of oblique sEEG trajectories. In this study, the authors evaluated the relative accuracy and efficacy of both orthogonal and oblique trajectories during robotic implantation of sEEG electrodes to sample seizure networks.

METHODS

The authors performed a retrospective analysis of 150 consecutive procedures in 134 patients, accounting for 2040 electrode implantations. Of these, 837 (41%) were implanted via oblique trajectories (defined as an entry angle > 30°). Accuracy was calculated by comparing the deviation of each electrode at the entry and the target point from the planned trajectory using postimplantation imaging.

RESULTS

The mean entry and target deviations were 1.57 mm and 1.89 mm for oblique trajectories compared with 1.38 mm and 1.69 mm for orthogonal trajectories, respectively. Entry point deviation was significantly associated with entry angle, but the impact of this relationship was negligible (-0.015-mm deviation per degree). Deviation at the target point was not significantly affected by the entry angle. No hemorrhagic or infectious complications were observed in the entire cohort, further suggesting that these differences were not meaningful in a clinical context. Of the patients who then underwent definitive procedures after sEEG, 69 patients had a minimum of 12 months of follow-up, of whom 58 (84%) achieved an Engel class I or II outcome during a median follow-up of 27 months.

CONCLUSIONS

The magnitude of stereotactic errors in this study falls squarely within the range reported in the sEEG literature, which primarily features orthogonal trajectories. The patient outcomes reported in this study suggest that seizure foci are well localized using oblique trajectories. Thus, the selective use of oblique trajectories in the authors' cohort was associated with excellent safety and efficacy, with no patient incidents, and the findings support the use of oblique trajectories as an effective and safe means of investigating seizure networks.

Robotic Applications in Cranial Neurosurgery: Current and Future

Robotics applied to cranial surgery is a fast-moving and fascinating field, which is transforming the practice of neurosurgery. With exponential increases in computing power, improvements in connectivity, artificial intelligence, and enhanced precision of accessing target structures, robots are likely to be incorporated into more areas of neurosurgery in the future-making procedures safer and more efficient. Overall, improved efficiency can offset upfront costs and potentially prove cost-effective. In this narrative review, we aim to translate a broad clinical experience into practical information for the incorporation of robotics into neurosurgical practice. We begin with procedures where robotics take the role of a stereotactic frame and guide instruments along a linear trajectory. Next, we discuss robotics in endoscopic surgery, where the robot functions similar to a surgical assistant by holding the endoscope and providing retraction, supplemental lighting, and correlation of the surgical field with navigation. Then, we look at early experience with endovascular robots, where robots carry out tasks of the primary surgeon while the surgeon directs these movements remotely. We briefly discuss a novel microsurgical robot that can perform many of the critical operative steps (with potential for fine motor augmentation) remotely. Finally, we highlight 2 innovative technologies that allow instruments to take nonlinear, predetermined paths to an intracranial destination and allow magnetic control of instruments for real-time adjustment of trajectories. We believe that robots will play an increasingly important role in the future of neurosurgery and aim to cover some of the aspects that this field holds for neurosurgical innovation.

The Path to Surgical Robotics in Neurosurgery

Robotic systems may help efficiently execute complicated tasks that require a high degree of accuracy, and this, in large part, explains why robotics have garnered widespread use in a variety of neurosurgical applications, including intracranial biopsies, spinal instrumentation, and placement of intracranial leads. The use of robotics in neurosurgery confers many benefits, and inherent limitations, to both surgeons and their patients. In this narrative review, we provide a historical overview of robotics and its implementation across various surgical specialties, and discuss the various robotic systems that have been developed specifically for neurosurgical applications. We also discuss the relative advantages of robotic systems compared to traditional surgical techniques, particularly as it pertains to integration of image guidance with the ability of the robotic arm to reliably execute pre-planned tasks. As more neurosurgeons adopt the use of robotics in their practice, we postulate that further technological advancements will become available that will help achieve improved technical capabilities, user experience, and overall patient clinical outcomes.

Robot-Assisted Insular Depth Electrode Implantation Through Oblique Trajectories: 3-Dimensional Anatomical Nuances, Technique, Accuracy, and Safety

BACKGROUND

The insula is a deep cortical structure that has renewed interest in epilepsy investigation. Invasive EEG recordings of this region have been challenging. Robot-assisted stereotactic electroencephalography has improved feasibility and safety of such procedures.

OBJECTIVE

To describe technical nuances of three-dimensional (3D) oblique trajectories for insular robot-assisted depth electrode implantation.

METHODS

Fifty patients who underwent robot-assisted depth electrode implantation between June 2017 and December 2018 were retrospectively analyzed. Insular electrodes were implanted through oblique, orthogonal, or parasagittal trajectories. Type of trajectories, accuracy, number of contacts within insular cortex, imaging, and complication rates were analyzed. Cadaveric and computerized tomography/magnetic resonance imaging 3D reconstructions were used to visualize insular anatomy and the technical implications of oblique trajectories.

RESULTS

Forty-one patients (98 insular electrodes) were included. Thirty (73.2%) patients had unilateral insular coverage. Average insular electrodes per patient was 2.4. The mean number of contacts was 7.1 (SD ± 2.91) for all trajectories and 8.3 (SD ± 1.51) for oblique insular trajectories. The most frequently used was the oblique trajectory (85 electrodes). Mean entry point error was 1.5 mm (0.2-2.8) and target error was 2.4 mm (0.8-4.0), 2.0 mm (1.1-2.9) for anterior oblique and 2.8 mm (0.8-4.9) for posterior oblique trajectories. There were no complications related to insular electrodes.

CONCLUSION

Oblique trajectories are the preferred method for insular investigation at our institution, maximizing the number of contacts within insular cortex without traversing through sulci or major CSF fissures. Robot-assisted procedures are safe and efficient. 3D understanding of the insula's unique anatomical features can help the surgeon to improve targeting of this structure.

SYLVIUS: A multimodal and multidisciplinary platform for epilepsy surgery

BACKGROUND AND OBJECTIVE

We present SYLVIUS, a software platform intended to facilitate and improve the complex workflow required to diagnose and surgically treat drug-resistant epilepsies. In complex epilepsies, additional invasive information from exploration with stereoencephalography (SEEG) with deep electrodes may be needed, for which the input from different diagnostic methods and clinicians from several specialties is required to ensure diagnostic efficacy and surgical safety. We aim to provide a software platform with optimal data flow among the different stages of epilepsy surgery to provide smooth and integrated decision making.

METHODS

The SYLVIUS platform provides a clinical workflow designed to ensure seamless and safe patient data sharing across specialities. It integrates tools for stereo visualization, data registration, transfer of electrode plans referred to distinct datasets, automated postoperative contact segmentation, and novel DWI tractography analysis. Nineteen cases were retrospectively evaluated to track modifications from an initial plan to obtain a final surgical plan, using SYLVIUS.

RESULTS

The software was used to modify trajectories in all 19 consulted cases, which were then imported into the robotic system for the surgical intervention. When available, SYLVIUS provided extra multimodal information, which resulted in a greater number of trajectory modifications.

CONCLUSIONS

The architecture presented in this paper streamlines epilepsy surgery allowing clinicians to have a digital clinical tool that allows recording of the different stages of the procedure, in a common multimodal 2D/3D setting for participation of different clinicians in defining and validating surgical plans for SEEG cases.

Gray Matter Sampling Differences Between Subdural Electrodes and Stereoelectroencephalography Electrodes

Objective: Stereoelectroencephalography (SEEG) has seen a recent increase in popularity in North America; however, concerns regarding the spatial sampling capabilities of SEEG remain. We aimed to quantify and compare the spatial sampling of subdural electrode (SDE) and SEEG implants.

Methods: Patients with drug-resistant epilepsy who underwent invasive monitoring were included in this retrospective case-control study. Ten SEEG cases were compared with ten matched SDE cases based on clinical presentation and pre-implantation hypothesis. To quantify gray matter sampling, MR and CT images were coregistered and a 2.5mm radius sphere was superimposed over the center of each electrode contact. The estimated recording volume of gray matter was defined as the cortical voxels within these spherical models. Paired t-tests were performed to compare volumes and locations of SDE and SEEG recording. A Ripley's K-function analysis was performed to quantify differences in spatial distributions.

Results: The average recording volume of gray matter by each individual contact was similar between the two modalities. SEEG implants sampled an average of 20% more total gray matter, consisted of an average of 17% more electrode contacts, and had 77% more of their contacts covering gray matter within sulci. Insular coverage was only achieved with SEEG. SEEG implants generally consist of discrete areas of dense local coverage scattered across the brain; while SDE implants cover relatively contiguous areas with lower density recording.

Significance: Average recording volumes per electrode contact are similar for SEEG and SDE, but SEEG may allow for greater overall volumes of recording as more electrodes can be routinely implanted. The primary difference lies in the location and distribution of gray matter than can be sampled. The selection between SEEG and SDE implantation depends on sampling needs of the invasive implant.

Cognitive and Emotional Mapping With SEEG

Mapping of cortical functions is critical for the best clinical care of patients undergoing epilepsy and tumor surgery, but also to better understand human brain function and connectivity. The purpose of this review is to explore existing and potential means of mapping higher cortical functions, including stimulation mapping, passive mapping, and connectivity analyses. We examine the history of mapping, differences between subdural and stereoelectroencephalographic approaches, and some risks and safety aspects, before examining different types of functional mapping. Much of this review explores the prospects for new mapping approaches to better understand other components of language, memory, spatial skills, executive, and socio-emotional functions. We also touch on brain-machine interfaces, philosophical aspects of aligning tasks to brain circuits, and the study of consciousness. We end by discussing multi-modal testing and virtual reality approaches to mapping higher cortical functions.

Hemorrhage Rates After Implantation and Explantation of Stereotactic Electroencephalography: Reevaluating Patients' Risk

OBJECTIVE

Stereoelectroencephalography (sEEG), despite its established usefulness, has not been thoroughly evaluated for its adverse events profile. In this study, hemorrhage rates were evaluated both per patient and per lead placed not only in the immediate postoperative period, but also over the course of admission and after explantation when available.

METHODS

This is a single-center retrospective study of pediatric and adult patients undergoing sEEG lead placement at a large urban hospital. All available postoperative imaging was reviewed for the presence of hemorrhage, including any imaging occurring throughout admission as well as within 1 month of lead explantation. Age and number of leads placed per procedure were compared using an unpaired t test assuming unequal variance.

RESULTS

A total of 1855 leads were placed in 147 cases. The mean age was 30.4 ±15.0 and the male/female ratio was 47:53. 9 leads (0.49%) in 9 cases (6.12%) were involved with postimplantation hemorrhage occurring on postoperative day 0.44 on average. Postexplantation imaging was available for 45 cases. Seven leads (1.40%) in 7 cases (15.56%) were involved with postexplantation hemorrhage occurring on average on postoperative day 1.42. There was a significant difference in mean age between patients with postexplantation hemorrhage versus control (45.0 vs. 32.2; P = 0.0277). No cases of hemorrhage required surgical intervention and no patients had permanent neurologic deficit.

CONCLUSIONS

Hemorrhage after sEEG lead implantation and explantation may be more common than previously reported. Consistent postexplantation imaging may be of clinical benefit in detecting hemorrhage that precludes patients from immediate discharge, particularly in older patients.

Accuracy of omni-planar and surface casting of epileptiform activity for intracranial seizure localization

OBJECTIVE

Intracranial electroencephalography (ICEEG) recordings are performed for seizure localization in medically refractory epilepsy. Signal quantifications such as frequency power can be projected as heatmaps on personalized three-dimensional (3D) reconstructed cortical surfaces to distill these complex recordings into intuitive cinematic visualizations. However, simultaneously reconciling deep recording locations and reliably tracking evolving ictal patterns remain significant challenges.

METHODS

We fused oblique magnetic resonance imaging (MRI) slices along depth probe trajectories with cortical surface reconstructions and projected dynamic heatmaps using a simple mathematical metric of epileptiform activity (line-length). This omni-planar and surface casting of epileptiform activity approach (OPSCEA) thus illustrated seizure onset and spread among both deep and superficial locations simultaneously with minimal need for signal processing supervision. We utilized the approach on 41 patients at our center implanted with grid, strip, and/or depth electrodes for localizing medically refractory seizures. Peri-ictal data were converted into OPSCEA videos with multiple 3D brain views illustrating all electrode locations. Five people of varying expertise in epilepsy (medical student through epilepsy attending level) attempted to localize the seizure-onset zones.

RESULTS

We retrospectively compared this approach with the original ICEEG study reports for validation. Accuracy ranged from 73.2% to 97.6% for complete or overlapping onset lobe(s), respectively, and ~56.1% to 95.1% for the specific focus (or foci). Higher answer certainty for a given case predicted better accuracy, and scorers had similar accuracy across different training levels.

SIGNIFICANCE

In an era of increasing stereo-EEG use, cinematic visualizations fusing omni-planar and surface functional projections appear to provide a useful adjunct for interpreting complex intracranial recordings and subsequent surgery planning.

Intracranial monitoring contributes to seizure freedom for temporal lobectomy patients with nonconcordant preoperative data

Objective

The question of whether a patient with presumed temporal lobe seizures should proceed directly to temporal lobectomy surgery versus undergo intracranial monitoring arises commonly. We evaluate the effect of intracranial monitoring on seizure outcome in a retrospective cohort of consecutive subjects who specifically underwent an anterior temporal lobectomy (ATL) for refractory temporal lobe epilepsy (TLE).

Methods

We performed a retrospective analysis of 85 patients with focal refractory TLE who underwent ATL following: (a) intracranial monitoring via craniotomy and subdural/depth electrodes (SDE/DE), (b) intracranial monitoring via stereotactic electroencephalography (sEEG), or (c) no intracranial monitoring (direct ATL—dATL). For each subject, the presurgical primary hypothesis for epileptogenic zone localization was characterized as unilateral TLE, unilateral TLE plus (TLE+), or TLE with bilateral/poor lateralization.

Results

At one‐year and most recent follow‐up, Engel Class I and combined I/II outcomes did not differ significantly between the groups. Outcomes were better in the dATL group compared to the intracranial monitoring groups for lesional cases but were similar in nonlesional cases. Those requiring intracranial monitoring for a hypothesis of TLE+had similar outcomes with either intracranial monitoring approach. sEEG was the only approach used in patients with bilateral or poorly lateralized TLE, resulting in 77.8% of patients seizure‐free at last follow‐up. Importantly, for 85% of patients undergoing SEEG, recommendation for ATL resulted from modifying the primary hypothesis based on iEEG data.

Significance

Our study highlights the value of intracranial monitoring in equalizing seizure outcomes in difficult‐to‐treat TLE patients undergoing ATL.

Accuracy and Feasibility Analysis of SEEG Electrode Implantation using the VarioGuide Frameless Navigation System in Patients with Drug-Resistant Epilepsy

OBJECTIVE

 The objective of the study was to evaluate the feasibility and accuracy of frameless stereoelectroencephalography (SEEG) electrode implantation in patients with drug-resistant epilepsy using the VarioGuide system.

METHODS

 The VarioGuide frameless navigation system was used to implant SEEG electrodes in patients with medically drug-resistant epilepsy. Demographic data, surgery duration, number of electrodes, and complications were retrospectively analyzed. Accuracy was compared by measuring the distance between the planned and actual electrode positions as determined by postoperative computed tomography images.

RESULTS

 A total of 141 SEEG electrodes were implanted in 19 patients from May 2015 to December 2018 with an average of 7.42 (range: 4-10) leads per patient. The average entry point localization error (EPLE) was 1.96 ± 0.47 mm (range: 0.32-3.29) and average target point localization error (TPLE) was 2.47 ± 0.79 mm (range: 0.72-4.83). The average operating time per lead (OTPL) was 14.16 ± 2.68 minutes (range: 8.64-21.58). No complications occurred.

CONCLUSION

 The VarioGuide frameless navigation system can be an effective method for SEEG electrode implantation in patients with drug-resistant epilepsy, particularly when the electrodes are concentrated in a relatively small region and the number of implanted electrodes is small.

A History of Diagnostic Investigations in Epilepsy Surgery

Epilepsy surgery has progressed significantly in the last 150 years. Functional brain maps allowed for the localization of epileptogenic lesions based on seizure patterns, allowing surgeons like McEwan and Horsely to treat epilepsy surgically. Berger's electroencephalogram marked the first modality directly identifying epileptic abnormalities. Penfield and Jasper collaborated, as neurosurgeon and neurologist, to use EEG for surgery. Meanwhile, Wada developed the amobarbital test, improving the protection of language and memory. Talairach and Bancaud pioneered invasive monitoring of deep brain activity with stereoelectroencephalography before the computer age made CT and MRI possible. Looking forward, AI and robotics hold promise for further improving outcomes.

Histological assessment of a chronically implanted cylindrically-shaped, polymer-based neural probe in the monkey

OBJECTIVE

Previous studies demonstrated the possibility to fabricate stereo-electroencephalography (SEEG) probes with high channel count and great design freedom, which incorporate macro- as well as micro-electrodes offering potential benefits for the pre-surgical evaluation of drug resistant epileptic patients. These new polyimide probes allowed to record local field potentials and multi-unit activity in the macaque monkey as early as one hour after implantation, yielding stable single-unit activity for up to 26 days after implantation. The findings opened new perspectives for investigating mechanisms underlying focal epilepsy and its treatment, but before moving to possible human applications, safety data are needed. Thus, in the present study we evaluate the biocompatibility of this new neural interface by assessing post-mortem the reaction of brain tissue along and around the probe implantation site.

APPROACH

Three probes were implanted, independently, in the brain of one monkey (Macaca mulatta) at different times. We used specific immunostaining methods for visualizing neuronal cells and astrocytes, for measuring the extent of damage caused by the probe and for relating it with the implantation time.

MAIN RESULTS

The size of the region where neurons cannot be detected did not exceed the size of the probe, indicating that a complete loss of neuronal cells is only present where the probe was physically positioned in the brain. Furthermore, around the probe shank, we observed a slightly reduced number of neurons within a radius of 50 µm and a modest increase in the number of astrocytes within 100 µm.

SIGNIFICANCE

In the light of previous electrophysiological findings, the present biocompatibility data suggest the potential usefulness and safety of this probe for human applications.