Stereoelectroencephalography Electrode Placement Research Articles

Stealth Autoguide as Robotic Holder for Cranial Endoscopic Surgery: Technical Note and Proof of Concept

The Stealth Autoguide (Medtronic, Minneapolis, USA) is a robotic auto-targeting device for stereotactic brain biopsy, placement of stereoelectroencephalography electrodes, and laser ablation therapy. This paper evaluates its off-label application as robotic endoscope holder in transnasal and intraventricular neurosurgery. The potential to enhance stability, reduce manual adjustments, and improve surgical precision is discussed, alongside cost-effectiveness and feasibility. Patients who underwent endoscopic endonasal, transventricular, and microsurgical endoscopic-assisted surgeries using the Stealth Autoguide as robotic holder from August 2023 to March 2024 were included. Surgical data and surgeons' remarks on advantages, disadvantages and limitations of the technique were collected. In this preliminary experience, Stealth Autoguide has proven safe and effective for several approaches. It was successfully used for patients with sellar, parasellar and suprasellar lesions. Moreover, the holder was employed in a third ventriculocisternostomy, a septostomy, and a removal of intraventricular lesion. Finally, the Autoguide has been a useful holder for the endoscope after gross total microsurgical excision of a tumor: the robot aligned the endoscope to the chosen trajectory and allowed the surgeon to "look around the corner" and confirm the extent of resection. No complications occurred in the treated cases, and the system provided great stability and usefulness throughout the surgeries. This experience proves that the Stealth Autoguide can be safely and effectively used as a robotic support for endoscopic procedures. This device ensures precise positioning and manipulation of neuroendoscopes, facilitating visualization and targeting of the desired area. Further researches are needed to verify applications and limitations.

Safety and accuracy of stereoelectroencephalography for pediatric and young adult patients with prior craniotomy.

The authors assessed the safety and accuracy of stereoelectroencephalography (SEEG) electrode implantation in pediatric patients who had previously undergone craniotomy compared to those without prior cranial surgery. The authors performed a retrospective analysis of patients under 25 years of age with medically refractory epilepsy at a single institution who underwent SEEG electrode placement between March 2016 and July 2023. Surgical history and demographic characteristics were collected from the electronic medical records. The coordinates of the anchor bolts and their respective SEEG electrode contacts were manually annotated using postoperative head CT scans. Bolt coordinates were used to calculate the initiated electrode trajectory set by the bolt by using the least-squares method to define a line along the bolt, projected along the length of the electrode. The shortest distance from each electrode contact to this line was calculated to obtain the error measurement. Statistical analysis was conducted using the Kolmogorov-Smirnov test to compare the distribution of errors between groups, the Student t-test was used for continuous variables, and the chi-square/Fisher's exact test was used for categorical variables. Fifty-eight patients underwent a total of 60 SEEG placements and met the inclusion criteria. Eighteen had a history of prior craniotomy and 40 without prior surgery, indicating entirely native cranial bone. Mean age, sex, and mean number of electrodes implanted per surgery were similar between groups. For the electrode contact furthest from the bolt, a mean (IQR) deviation of 1.32 (0.73-2.53) mm was noted for the prior craniotomy group and 1.08 (0.65-1.55) mm for the native bone group (p < 0.0001). A greater number of outliers for the contact furthest from the bolt, defined as > 6 mm from the initiated electrode trajectory, was seen in the prior craniotomy group (p < 0.0001). The complication rate was low and not statistically different between groups. The authors' analysis draws attention to the effect of the intracranial biomechanical environment along the path of the electrode after traversing past the anchor bolt and found that prior craniotomy was associated with a higher number of contacts with a significant deviation from the initiated trajectory. Despite these deviations, we did not find a difference in the overall low complication rate in both groups. Therefore, the authors conclude that SEEG electrode placement is a safe option in pediatric patients even after prior craniotomy.

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

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. 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. 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. 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.

Initial United States experience with Medtronic Stealth Autoguide cranial robotic guidance platform.

Stereotactic techniques play an important role in neurosurgery. The development of a miniaturized cranial robot with an efficient workflow and accurate surgical execution is an important step in a broader application of these techniques. Herein, the authors describe their experience with the Medtronic Stealth Autoguide miniaturized cranial robot. A retrospective review of 75 cases from 2020 to 2022 was performed. The patients who had undergone surgery utilizing the Stealth Autoguide robot were analyzed for surgical indication and accuracy, operative time, and clinical outcome. The outcomes were defined as follows: for stereoelectroencephalography (SEEG), the electrode placement pattern that identified the seizure focus and did not require any revision or additional leads; for biopsy, the percentage of cases in which diagnostic tissue was obtained; and for laser interstitial thermal therapy (LITT), the percentage of cases in which laser fiber placement was adequate for ablation. Surgical complications were defined as any asymptomatic or symptomatic intracerebral hemorrhage, new neurological deficit, or need for electrode, laser fiber, or biopsy needle repositioning or revision. The Stealth Autoguide robot was utilized in 75 on-label cases, including 40 SEEG cases for seizure focus localization, 19 LITT cases, and 16 stereotactic biopsy cases. The mean real target error (RTE) at the entry was 1.48 ± 0.84 mm for biopsy, 1.36 ± 0.89 mm for Visualase laser fiber placement, and 1.24 ± 0.72 mm for SEEG. The mean RTE at the target was 1.56 ± 0.95 mm for biopsy needle placement, 1.42 ± 0.93 mm for Visualase laser fiber placement, and 1.31 ± 0.87 mm for SEEG electrode placement. The surgical time for unilateral SEEG cases took an average 52 minutes (average 6.5 mins/lead, average 8 electrodes). Bilateral SEEG cases took an average 105 minutes (average 7.5 mins/lead, average 14 electrodes). In the SEEG population, there were no revised or unsuccessful seizure localizations. For biopsy, diagnostic tissue was obtained in 100% of cases. For LITT, fiber placement was adequate for ablation in 100% of cases. There were no cases of symptomatic or asymptomatic intracerebral hemorrhage, and no cases required repositioning or replacement of the laser fiber, electrode, or biopsy needle. One patient experienced transient cranial nerve III palsy following laser ablation that resolved in 10 weeks. A failure of communication between the robotic platform and the Stealth Autoguide as a station required the cancellation of 1 procedure. The Medtronic Stealth Autoguide robot system is versatile across biopsy, SEEG, and laser ablation indications. Setup and surgical execution are efficient with a high degree of accuracy and consistency.

Ictal Semiology Important for Electrode Implantation and Interpretation of Stereoelectroencephalography.

Scalp video-electroencephalography (video-EEG) monitoring should be analyzed thoroughly to preoperatively evaluate stereoelectroencephalography (SEEG). Formulating the working hypotheses for the epileptogenic zone (EZ) considering "anatomo-electroclinical correlations" is the most crucial step, which determines the placement of SEEG electrodes. If these hypotheses are insufficient, precise EZ identification may not be achieved during SEEG recording.In ictal semiology analysis, temporal and spatial patterns with reference to ictal EEG changes are emphasized. In frontal lobe epilepsy, seizures often begin with relatively widespread synchronous activity, and complex motor symptoms manifest within seconds. Due to the wide area involved and intense interhemispheric connectivity, a comprehensive evaluation is often required. Hypotheses are formulated on the basis of the motor symptoms and emotional manifestations that are related to the prefrontal cortices. In temporal lobe epilepsy, EEG onset often precedes clinical onset. Propagation from the EZ to locations within and outside of the temporal lobe is examined from both the EEG and semiological standpoint. The characteristics of contralateral versive seizures, contralateral tonic seizures, and frequent focal onset bilateral tonic-clonic seizures indicate a higher risk of temporo-perisylvian epilepsy. In parietal/occipital lobe epilepsy, despite that some symptoms result from activity in the immediate vicinity, stronger connectivity with other regions usually contributes to the generation of prominent ictal semiology. Hence, multilobar electrode placement is often useful in practice. For insular epilepsy, it is important to understand the anatomy, function, and networks between other regions. A semiological approach is one of the most important clues for electrode implantation and interpretation of SEEG.

Approach, complications, and outcomes for 37 consecutive pediatric patients undergoing laser ablation for medically refractory epilepsy at Stanford Children's Health.

The objective of this study was to better understand the safety and efficacy of laser interstitial thermal therapy (LITT) for children with medically refractory epilepsy. Thirty-seven consecutive pediatric epilepsy patients at a single pediatric center who underwent LITT ablation of epileptogenic foci between May 2017 and December 2021 were retrospectively reviewed. Patient demographics, medication use, seizure frequency, prior surgical interventions, procedural details, and pre- and postoperative seizure history were analyzed. Thirty-seven pediatric patients (24 male, 13 female) with severe medically refractory epilepsy were included; all underwent stereo-electroencephalography (SEEG) prior to LITT. The SEEG electrode placement was based on the preoperative workup and tailored to each patient by the epileptologist and neurosurgeons working together to identify the epileptic network and hopefully quiet borders. Seizure onset was at a mean age of 2.70 ± 2.82 years (range 0.25-12 years), and the mean age at the time of LITT was 9.46 ± 5.08 years (range 2.41-17.86 years). Epilepsy was lesional in 23 patients (18 tuberous sclerosis, 4 focal cortical dysplasia, 1 gliosis) and nonlesional in 14. Eighteen patients had prior surgical interventions including open resections (n = 13: 11 single and 2 multiple), LITT (n = 4), or both (n = 1). LITT targeted a region adjacent to the previous target in 5 cases. The median number of lasers placed during the procedure was 3 (range 1-5). Complications occurred in 14 (37.8%) cases, only 3 (8.11%) of which resulted in a permanent deficit: 1 venous hemorrhage requiring evacuation following laser ablation, 1 aseptic meningitis, 2 immediate postoperative seizures, and 10 neurological deficits (7 transient and 3 permanent). Postoperatively, 22 (59.5%) patients were seizure free at the last follow-up (median follow-up 18.35 months, range 7.40-48.76 months), and the median modified Engel class was I (Engel class I in 22 patients, Engel class II in 2, Engel class III in 2, and Engel class IV in 11). Patients having tried a greater number of antiseizure medications before LITT were less likely to achieve seizure improvement (p = 0.046) or freedom (p = 0.017). Seizure improvement following LITT was associated with a shorter duration of epilepsy prior to LITT (p = 0.044), although postoperative seizure freedom was not associated with a shorter epilepsy duration (p = 0.667). Caregivers reported postoperative neurocognitive improvement in 17 (45.9%) patients. In this large single-institution cohort of pediatric patients with medically refractory seizures due to various etiologies, LITT was a relatively safe and effective surgical approach for seizure reduction and seizure freedom at 1 year of follow-up.

PO095 / #613 STEREOELECTROENCEPHALOGRAPHY OF THE INSULAR CORTEX WITH INTRAOPERATIVE O-ARM. OUR EXPERIENCE AND RESULTS: E-POSTER VIEWING

Refractory epilepsy affects 30% of epileptic patients, with devastating consequences for their personal and professional development. Of those, about 40% could benefit from surgical treatment, provided there is an identifiable accessible epileptic focus. When non-invasive diagnosis is inconclusive, further study is warranted by incursive registration of electrical brain activity with either subdural, epidural or deep electrodes. The latter, known as stereoelectroencephalography (SEEG), displays a three dimensional representation of the epileptic zone and permits identification of subcortical aberrancies. Traditional frame-based or the novel robotic-based stereotactic placement of deep electrodes, though very precise, are cumbersome and expensive. Thus, we propose a frameless neuronavigation technique, combined with intraoperative imaging, as a reliable and straightforward alternative. We present our experience and results with an intraoperative 3D fluoroscopic device and an articulated passive arm for SEEG electrode placement.

Neuropathologic changes associated with stereoelectroencephalography depth electrode placement.

The aim of this study was to detail the neuropathologic changes resulting from the surgical placement of stereoelectroencephalography (SEEG) leads in an initial small group of epilepsy cases and to raise awareness of this iatrogenic pathology, especially to those medical providers who specialize in the care of epilepsy patients. Five consecutive patients who underwent epilepsy resection surgery following SEEG monitoring at OSF Saint Francis Medical Center were included in our report. Resection specimens were examined grossly and entirely submitted for microscopic evaluation by a neuropathologist. Seizure-related pathologies, as well as histologic changes related to SEEG electrode placement, were documented. The patient cohort included two females and three males, with an age range of 9 to 47 years. Neuropathologic examination revealed one or more seizure-related pathologies in each patient's resection specimen. In addition, all brain resection specimens showed multiple microinfarcts, which appeared to correlate with the placement and size of SEEG electrodes. Patchy leptomeningeal chronic inflammation was also seen in most cases. SEEG electrode placement is an effective procedure for determining epileptogenic regions and guiding subsequent resection surgeries in medically refractory epilepsy. Multiple microinfarcts and chronic inflammation are commonly seen in brain resection specimens following SEEG electrode insertion, but studies detailing these iatrogenic histopathologic changes are lacking. The clinical significance and long-term implications of multiple small foci of electrode-induced injury that remain in the patient's brain after resection of the epileptogenic focus are unknown and may provide a welcome area for future study.

Robot-Assisted Stereoelectroencephalography: 2-Dimensional Operative Video.

Invasive neuromonitoring is an important component of presurgical workup and seizure onset zone localization in patients with epilepsy being considered for surgical resection. In the United States, intraparenchymal stereoelectroencephalography (SEEG) electrodes have been replacing subdural grid electrodes for most cases, following a trend that has already matured in Europe. The use of robotic assistance has been shown to improve operative times and accuracy in SEEG electrode placement, as users benefit from the embedded planning software as well as the efficiency and accuracy of the robotic arm. The greatest barriers to implementation of this technology are the upfront cost and learning curve. This case-based surgeon's perspective operative video could benefit those considering incorporating robotic assistance for SEEG electrode placement. Those considering robotic assistance for pedicle screw placement and other budding applications may also benefit, as well as innovators looking for new applications. The patient consented for the procedure, video recording, and inclusion in subsequent publications.

Validation of 3D fluoroscopy for image-guidance registration in depth electrode implantation for medically refractory epilepsy.

Frame registration is a critical step to ensure accurate electrode placement in stereotactic procedures such as stereoelectroencephalography (SEEG) and is routinely done by merging a computed tomography (CT) scan with the preoperative magnetic resonance (MR) examination. Three-dimensional fluoroscopy (XT) has emerged as a method for intraoperative electrode verification following electrode implantation and more recently has been proposed as a registration method with several advantages. We compared the accuracy of SEEG electrode placement by frame registration with CT and XT imaging by analyzing the Euclidean distance between planned and post-implantation trajectories of the SEEG electrodes to calculate the error in both the entry (EP) and target (TP) points. Other variables included radiation dose, efficiency, and complications. Twenty-seven patients (13 CT and 14 XT) underwent placement of SEEG electrodes (319 in total). The mean EP and TP errors for the CT group were 2.3 mm and 3.3 mm, respectively, and 1.9 mm and 2.9 mm for the XT group, with no statistical difference (p = 0.75 and p = 0.246). The time to first electrode placement was similar (XT, 82 ± 10 min; CT, 84 ± 22 min; p = 0.858) and the average radiation exposure with XT (234 ± 55 mGy*cm) was significantly lower than CT (1245 ± 123 mGy*cm) (p < 0.0001). Four complications were documented with equal incidence in both groups. The use of XT as a method for registration resulted in similar implantation accuracy compared with CT. Advantages of XT are the substantial reduction in radiation dose and the elimination of the need to transfer the patient out of the room which may have an impact on patient safety and OR efficiency.

Stereoelectroencephalography electrode placement: Detection of blood vessel conflicts.

ObjectiveVarious forms of vascular imaging are performed to identify vessels that should be avoided during stereoelectroencephalography (SEEG) planning. Digital subtraction angiography (DSA) is the gold standard for intracranial vascular imaging. DSA is an invasive investigation, and a balance is necessary to identify all clinically relevant vessels and not to visualize irrelevant vessels that may unnecessarily restrict electrode placement. We sought to estimate the size of vessels that are clinically significant for SEEG planning.MethodsThirty‐three consecutive patients who underwent 354 SEEG electrode implantations planned with computer‐assisted planning and DSA segmentation between 2016 and 2018 were identified from a prospectively maintained database. Intracranial positions of electrodes were segmented from postimplantation computed tomography scans. Each electrode was manually reviewed using “probe‐eye view” with the raw preoperative DSA images for vascular conflicts. The diameter of vessels and the location of conflicts were noted. Vessel conflicts identified on raw DSA images were cross‐referenced against other modalities to determine whether the conflict could have been detected.ResultsOne hundred sixty‐six vessel conflicts were identified between electrodes and DSA‐identified vessels, with 0‐3 conflicts per electrode and a median of four conflicts per patient. The median diameter of conflicting vessels was 1.3 mm (interquartile range [IQR] = 1.0‐1.5 mm). The median depth of conflict was 31.0 mm (IQR = 14.3‐45.0 mm) from the cortical surface. The addition of sulcal models to DSA, magnetic resonance venography (MRV), and T1 + gadolinium images, as an exclusion zone during computer‐assisted planning, would have prevented the majority of vessel conflicts. We were unable to determine whether vessels were displaced or transected by the electrodes.SignificanceVascular segmentation from DSA images was significantly more sensitive than T1 + gadolinium or MRV images. Electrode conflicts with vessels 1‐1.5 mm in size did not result in a radiologically detectable or clinically significant hemorrhage and could potentially be excluded from consideration during SEEG planning.

Robotic Stereotaxy in Cranial Neurosurgery: A Qualitative Systematic Review.

Modern-day stereotactic techniques have evolved to tackle the neurosurgical challenge of accurately and reproducibly accessing specific brain targets. Neurosurgical advances have been made in synergy with sophisticated technological developments and engineering innovations such as automated robotic platforms. Robotic systems offer a unique combination of dexterity, durability, indefatigability, and precision. To perform a systematic review of robotic integration for cranial stereotactic guidance in neurosurgery. Specifically, we comprehensively analyze the strengths and weaknesses of a spectrum of robotic technologies, past and present, including details pertaining to each system's kinematic specifications and targeting accuracy profiles. Eligible articles on human clinical applications of cranial robotic-guided stereotactic systems between 1985 and 2017 were extracted from several electronic databases, with a focus on stereotactic biopsy procedures, stereoelectroencephalography, and deep brain stimulation electrode insertion. Cranial robotic stereotactic systems feature serial or parallel architectures with 4 to 7 degrees of freedom, and frame-based or frameless registration. Indications for robotic assistance are diversifying, and include stereotactic biopsy, deep brain stimulation and stereoelectroencephalography electrode placement, ventriculostomy, and ablation procedures. Complication rates are low, and mainly consist of hemorrhage. Newer systems benefit from increasing targeting accuracy, intraoperative imaging ability, improved safety profiles, and reduced operating times. We highlight emerging future directions pertaining to the integration of robotic technologies into future neurosurgical procedures. Notably, a trend toward miniaturization, cost-effectiveness, frameless registration, and increasing safety and accuracy characterize successful stereotactic robotic technologies.

Application of stereoelectroencephalography in preoperative assessment of patients with drug-refractory epilepsy

Objective To investigate the application value of stereoelectroencephalography (SEEG) in the preoperative assessment of epilepsy surgery. Methods The clinical data of 78 patients with drug-refractory epilepsy assessed with SEEG before procedure at the Epilepsy Center, Guangdong 999 Brain Hospital from April 2014 to April 2015 were analyzed retrospectively. The noninvasive assessment was conducted first, and the SEEG electrode placement scheme was designed according to the clinical and imaging data, and then under the guidance of robotized stereotactic assistant (ROSA), the electrode implantation was completed. The SEEG monitoring was conducted in order to complete the resection of epileptogenic zone finally under the guidance of neuronavigation. Results Seventy-eight patients completed 81 SEEG electrode implantations (3 patients had additional electrode implantations), including 16 (20.5%) bilateral implantations. A total of 940 SEEG electrodes were implanted and the average number of implanted electrodes was 12.3 per case. Only 1 patient had an epidural hematoma in the electrode region, and other patients did not have the complications, such as serious hemorrhage, infection, cerebrospinal fluid leakage, electrode fraction or displacement. Seventy-six patients successfully completed the resection of epileptogenic zone, and 2 patients failed to undergo surgery. Fifty-nine patients were followed up for 6-18 months. The seizure control for Engel rating grades were grade Ⅰ in 47 cases (79.7%), grade Ⅱ in 2 cases (3.4%), grade Ⅲ in 6 cases (10.2%), and grade Ⅳ in 4 cases (6.8%). In 51 patients with MRI positive, the Engel grade Ⅰ was in 42 cases (82.4%); in 8 patients with MRI negative, the Engel grade Ⅰ was in 5 cases. There was no significant difference in the seizure control rate between the 2 groups (P>0.05). Conclusion The surgical treatment of epilepsy under the guidance of SEEG is both safe and effective. Key words: Epilepsy; Electroencephalography; Stereoelectroencephalography; Robotized stereotactic assistant; Multimodel images

The stereotactic approach for mapping epileptic networks: a prospective study of 200 patients.

Stereoelectroencephalography (SEEG) is a methodology that permits accurate 3D in vivo electroclinical recordings of epileptiform activity. Among other general indications for invasive intracranial electroencephalography (EEG) monitoring, its advantages include access to deep cortical structures, its ability to localize the epileptogenic zone when subdural grids have failed to do so, and its utility in the context of possible multifocal seizure onsets with the need for bihemispheric explorations. In this context, the authors present a brief historical overview of the technique and report on their experience with 2 SEEG techniques (conventional Leksell frame-based stereotaxy and frameless stereotaxy under robotic guidance) for the purpose of invasively monitoring difficult-to-localize refractory focal epilepsy. Over a period of 4 years, the authors prospectively identified 200 patients with refractory epilepsy who collectively underwent 2663 tailored SEEG electrode implantations for invasive intracranial EEG monitoring and extraoperative mapping. The first 122 patients underwent conventional Leksell frame-based SEEG electrode placement; the remaining 78 patients underwent frameless stereotaxy under robotic guidance, following acquisition of a stereotactic ROSA robotic device at the authors' institution. Electrodes were placed according to a preimplantation hypothesis of the presumed epileptogenic zone, based on a standardized preoperative workup including video-EEG monitoring, MRI, PET, ictal SPECT, and neuropsychological assessment. Demographic features, seizure semiology, number and location of implanted SEEG electrodes, and location of the epileptogenic zone were recorded and analyzed for all patients. For patients undergoing subsequent craniotomy for resection, the type of resection and procedure-related complications were prospectively recorded. These results were analyzed and correlated with pathological diagnosis and postoperative seizure outcomes. The epileptogenic zone was confirmed by SEEG in 154 patients (77%), of which 134 (87%) underwent subsequent craniotomy for epileptogenic zone resection. Within this cohort, 90 patients had a minimum follow-up of at least 12 months; therein, 61 patients (67.8%) remained seizure free, with an average follow-up period of 2.4 years. The most common pathological diagnosis was focal cortical dysplasia Type I (55 patients, 61.1%). Per electrode, the surgical complications included wound infection (0.08%), hemorrhagic complications (0.08%), and a transient neurological deficit (0.04%) in a total of 5 patients (2.5%). One patient (0.5%) ultimately died due to intracerebral hematoma directly ensuing from SEEG electrode placement. Based on these results, SEEG methodology is safe, reliable, and effective. It is associated with minimal morbidity and mortality, and serves as a practical, minimally invasive approach to extraoperative localization of the epileptogenic zone in patients with refractory epilepsy.