Invasive EEG explorations

Clinical utility and safety of a trapezoid-shaped electrode placement for evaluating the mesio-basal temporal lobe during epilepsy surgery

A trapezoid-shaped electrode (TSE) is used for detecting epileptogenicity in patients with temporal lobe epilepsy (TLE). However, the utility and safety associated with TSE placement have not been reported. In this study, we evaluated the safety and usefulness of TSE by analyzing the seizure detection, surgical outcomes and complications in patients with TLE who underwent intracranial electrodes (ICE) placement. Between April 2000 and August 2019, 50 patients with TLE who underwent 51 ICE placement procedures were examined. A TSE with eight contacts covering the parahippocampal gyrus and basal temporal lobe was used. Among the 37 patients who underwent TSE placement, 26 and 11 patients were diagnosed with mesial TLE (mTLE) and extra-mTLE, respectively. The 14 remaining patients without TSE placement were diagnosed with extra-mTLE. Seizure freedom was achieved in 73% (19/26) of mTLE patients detected by TSE and 50% (14/24) of extra-mTLE patients.Good seizure outcomes (Engel class I and II) were observed in 81% (21/26) patients with mTLE and 67% (16/24) patients with extra-mTLE. Radiographic complications were observed in 20% (10/50) patients who underwent ICE placement. Although 6% (3/50) patients showed transient neurological deficits, none were permanent. The electrodes responsible for the occurrence of complications included nine grid electrodes and one TSE. The complication rate after TSE placement was 3% (1/37). More than 64 electrode contacts and male sex, not TSE placement, were identified as significant risk factors for developing complications. This study demonstrated the usefulness and safety of TSE for evaluating mTLE in patients undergoing ICE placement.

Stereoelectroencephalography: a review of complications and outcomes in a new Australian centre

BACKGROUND

Surgical management of refractory focal epilepsy requires preoperative localisation of the epileptogenic zone (EZ). To augment noninvasive studies, stereoelectroencephalography (SEEG) is being increasingly adopted as a form of intracranial monitoring.

AIMS

This study aimed to determine the rate of complications for patients undergoing SEEG and to report the success of SEEG with regard to EZ detection and seizure outcome following definitive surgery.

METHODS

A retrospective cohort design investigated all cases of SEEG at our institution. Surgical, anaesthetic and medical complications with subsequent epilepsy surgery and seizure outcome data were extracted from medical records. Multivariate logistic regression was used to investigate the relationship between both the number of electrodes per patient and the duration of SEEG recording with the rate of complications.

RESULTS

Sixty-four patients with 66 implantations were included. Headache was the most common complication (n = 54, 82%). There were no major surgical or medical complications. Two anaesthetic complications occurred. EZ localisation was successful in 63 cases (95%). Curative intent surgery was performed in 39 patients (59%) and 23 patients achieved an Engel class I outcome (59% of those undergoing surgery). The number of electrodes and duration of recording were not associated with complications.

CONCLUSIONS

No patients in our series experienced major surgical or medical complications and we have highlighted the challenges associated with neuroanaesthesia in SEEG. Our complication rates and seizure outcomes are equivalent to published literature indicating that this technique can be successfully established in newer centres using careful case selection. Standardised reporting of SEEG complications should be adopted.

Subdural electrodes versus stereoelectroencephalography for pediatric epileptogenic zone localization: a retrospective cohort study

OBJECTIVE

The objective of this study was to compare the relative safety and effectiveness of invasive monitoring with subdural electrodes (SDEs) and stereoelectroencephalography (sEEG) in pediatric patients with drug-resistant epilepsy.

METHODS

A retrospective cohort study was performed in 176 patients who underwent invasive monitoring evaluations at UPMC Children’s Hospital of Pittsburgh between January 2000 and September 2021. To examine differences between SDE and sEEG groups, independent-samples t-tests for continuous variables and Pearson chi-square tests for categorical variables were performed. A p value < 0.1 was considered statistically significant.

RESULTS

There were 134 patients (76%) in the SDE group and 42 (24%) in the sEEG group. There was a difference in the proportion with complications (17.9% in the SDE group vs 7.1% in the sEEG group, p = 0.09) and resection (75.4% SDE vs 21.4% sEEG, p < 0.01) between SDE and sEEG patients. However, there was no observable difference in the rates of postresection seizure freedom at 1-year clinical follow-up (60.2% SDE vs 75.0% sEEG, p = 0.55).

CONCLUSIONS

These findings reveal a difference in rates of surgical complications and resection between SDEs and sEEG. Larger prospective, multi-institutional pediatric comparative effectiveness studies may further explore these associations.

PET/MRI in the Presurgical Evaluation of Patients with Epilepsy: A Concordance Analysis

The aim of our prospective study was to evaluate the clinical impact of hybrid [18F]-fluorodeoxyglucose positron emission tomography/magnetic resonance imaging ([18F]-FDG PET/MRI) on the decision workflow of epileptic patients with discordant electroclinical and MRI data. A novel mathematical model was introduced for a clinical concordance calculation supporting the classification of our patients by subgroups of clinical decisions. Fifty-nine epileptic patients with discordant clinical and diagnostic results or MRI negativity were included in this study. The diagnostic value of the PET/MRI was compared to other modalities of presurgical evaluation (e.g., electroclinical data, PET, and MRI). The results of the population-level statistical analysis of the introduced data fusion technique and concordance analysis demonstrated that this model could be the basis for the development of a more accurate clinical decision support parameter in the future. Therefore, making the establishment of “invasive” (operable and implantable) and “not eligible for any further invasive procedures” groups could be much more exact. Our results confirmed the relevance of PET/MRI with the diagnostic algorithm of presurgical evaluation. The introduction of a concordance analysis could be of high importance in clinical and surgical decision-making in the management of epileptic patients. Our study corroborated previous findings regarding the advantages of hybrid PET/MRI technology over MRI and electroclinical data.

Intracranial recordings in humans reveal specific hippocampal spectral and dorsal vs. ventral connectivity signatures during visual, attention and memory tasks

Invasive brain recordings using many electrodes across a wide range of tasks provide a unique opportunity to study the role of oscillatory patterning and functional connectivity. We used large-scale recordings (stereo EEG) within and beyond the human hippocampus to investigate the role of distinct frequency oscillations during real-time execution of visual, attention and memory tasks in eight epileptic patients. We found that activity patterns in the hippocampus showed task and frequency dependent properties. Importantly, we found distinct connectivity signatures, in particular concerning parietal-hippocampal connectivity, thus revealing large scale synchronization of networks involved in memory tasks. Comparing the power per frequency band, across tasks and hippocampal regions (anterior/posterior) we confirmed a main effect of frequency band (p = 0.002). Gamma band activity was higher for visuo-spatial memory tasks in the anterior hippocampus. Further, we found that alpha and beta band activity in posterior hippocampus had larger modulation for high memory load visual tasks (p = 0.004). Three functional connectivity task related networks were identified: (dorsal) parietal-hippocampus (visual attention and memory), ventral stream- hippocampus and hippocampal-frontal connections (mainly tasks involving face recognition or object based search). These findings support the critical role of oscillatory patterning in the hippocampus during visual and memory tasks and suggests the presence of task related spectral and functional connectivity signatures. These results show that the use of large scale human intracranial recordings can validate the role of oscillatory and functional connectivity patterns across a broad range of cognitive domains.

Improving Detection of Hippocampal Epileptiform Activity Using Magnetoencephalography

PURPOSE

Magnetoencephalography (MEG) defines the spike-generating zone and provides targets for invasive monitoring with stereotactic electroencephalography. This retrospective, blinded, cross-sectional study determined whether MEG virtual sensors could identify hippocampal epileptiform activity.

METHODS

Using MEG beamformer analysis, virtual sensors were manually placed in bilateral hippocampi and corresponding virtual sensor waveforms were analyzed for the presence of epileptiform activity. These findings were compared with hippocampal stereotactic electroencephalography in the same patients. Concordance was determined using sensitivity and specificity.

RESULTS

Thirty patients (mean age 12.5 ± 5.9 years) and 35 hippocampi were included. Patients were also placed into subgroups based on conventional MEG analysis: temporal (n = 19), extratemporal (n = 10), and normal (n = 1). Overall, sensitivity and specificity were 57.9% and 50.0%, respectively (n = 35). Patients with temporal sources based on conventional MEG analysis had sensitivity and specificity of 80.0% and 36.4%, respectively (n = 21). Those with extratemporal sources based on conventional MEG had sensitivity and specificity of 42.9% and 80.0%, respectively (n = 12).

CONCLUSIONS

When grouped by conventional MEG analysis, virtual sensors can be useful to confirm mesial temporal dipoles seen with conventional analysis.

SIGNIFICANCE

This work may help support the use of MEG for the detection of epileptiform activity in the hippocampus and influence the planning of invasive electrode placement.

Theoretical stereoelectroencephalography density on the brain convexity

INTRODUCTION

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

The role of hybrid FDG-PET/MRI on decision-making in presurgical evaluation of drug-resistant epilepsy

Background

When MRI fails to detect a potentially epileptogenic lesion, the chance of a favorable outcome after epilepsy surgery becomes significantly lower (from 60 to 90% to 20–65%). Hybrid FDG-PET/MRI may provide additional information for identifying the epileptogenic zone. We aimed to investigate the possible effect of the introduction of hybrid FDG-PET/MRI into the algorithm of the decision-making in both lesional and non-lesional drug-resistant epileptic patients.

Methods

In a prospective study of patients suffering from drug-resistant focal epilepsy, 30 nonlesional and 30 lesional cases with discordant presurgical results were evaluated using hybrid FDG-PET/MRI.

Results

The hybrid imaging revealed morphological lesion in 18 patients and glucose hypometabolism in 29 patients within the nonlesional group. In the MRI positive group, 4 patients were found to be nonlesional, and in 9 patients at least one more epileptogenic lesion was discovered, while in another 17 cases the original lesion was confirmed by means of hybrid FDG-PET/MRI. As to the therapeutic decision-making, these results helped to indicate resective surgery instead of intracranial EEG (iEEG) monitoring in 2 cases, to avoid any further invasive diagnostic procedures in 7 patients, and to refer 21 patients for iEEG in the nonlesional group. Hybrid FDG-PET/MRI has also significantly changed the original therapeutic plans in the lesional group. Prior to the hybrid imaging, a resective surgery was considered in 3 patients, and iEEG was planned in 27 patients. However, 3 patients became eligible for resective surgery, 6 patients proved to be inoperable instead of iEEG, and 18 cases remained candidates for iEEG due to the hybrid FDG-PET/MRI. Two patients remained candidates for resective surgery and one patient became not eligible for any further invasive intervention.

Conclusions

The results of hybrid FDG-PET/MRI significantly altered the original plans in 19 of 60 cases. The introduction of hybrid FDG-PET/MRI into the presurgical evaluation process had a potential modifying effect on clinical decision-making.

Trial registration

Trial registry: Scientific Research Ethics Committee of the Medical Research Council of Hungary. Trial registration number: 008899/2016/OTIG. Date of registration: 08 February 2016.

Developments in the human machine interface technologies and their applications: a review

Human-machine interface (HMI) techniques use bioelectrical signals to gain real-time synchronised communication between the human body and machine functioning. HMI technology not only provides a real-time control access but also has the ability to control multiple functions at a single instance of time with modest human inputs and increased efficiency. The HMI technologies yield advanced control access on numerous applications such as health monitoring, medical diagnostics, development of prosthetic and assistive devices, automotive and aerospace industry, robotic controls and many more fields. In this paper, various physiological signals, their acquisition and processing techniques along with their respective applications in different HMI technologies have been discussed.

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.

Use of Innovative SPECT Techniques in the Presurgical Evaluation of Patients with Nonlesional Extratemporal Drug-Resistant Epilepsy

Up to 30% of patients with epilepsy may not respond to antiepileptic drugs. Patients with drug-resistant epilepsy (DRE) should undergo evaluation for seizure onset zone (SOZ) localization to consider surgical treatment. Cases of drug-resistant nonlesional extratemporal lobe epilepsy (ETLE) pose the biggest challenge in localizing the SOZ and require multiple noninvasive diagnostic investigations before planning the intracranial monitoring (ICM) or direct resection. Ictal Single Photon Emission Computed Tomography (i-SPECT) is a unique functional diagnostic tool that assesses the SOZ using the localized hyperperfusion that occurs early in the seizure. Subtraction ictal SPECT coregistered to MRI (SISCOM), statistical ictal SPECT coregistered to MRI (STATISCOM), and PET interictal subtracted ictal SPECT coregistered with MRI (PISCOM) are innovative SPECT methods for the determination of the SOZ. This article comprehensively reviews SPECT and sheds light on its vital role in the presurgical evaluation of the nonlesional extratemporal DRE.

Cost-effectiveness analysis of invasive EEG monitoring in drug-resistant epilepsy

PURPOSE

Our aim was to determine the cost-effectiveness of two intracranial electroencephalography (iEEG) interventions: 1) stereoelectroencephalography (SEEG) and 2) placement of subdural grid electrodes (SDGs) both followed by resective surgery in patients with drug-resistant, partial-onset epilepsy, compared with medical management (MM) in Hungary from payer's perspective.

METHODS

The incremental health gains and costs of iEEG interventions have been determined with a combination of a decision tree and prevalence Markov process model over a 30-year time horizon in a cost-utility analysis (CUA). To address the effect of parameter uncertainty on the incremental cost-effectiveness ratio (ICER), deterministic and probabilistic sensitivity analyses were performed.

RESULTS

Our results showed that both SEEG and SDG interventions represent a more expensive but more effective strategy than MM representing the current standard of care. The total discounted cost of SEEG and SDG were € 32,760 and € 25,028 representing € 18,108 and € 10,375 additional cost compared with MM, respectively. However, they provide an additional 3.931 (in SEEG group) and 3.444 quality-adjusted life years (QALYs; in SDG group), correspondingly. Thus, the ICER of SEEG is € 4607 per QALY gain, while the ICER for SDG is € 3013 per QALY gain, compared with MM. At a cost-effectiveness threshold of € 41,058 per QALY in Hungary, both subtypes of iEEG interventions are cost-effective and provide good value for money.

SIGNIFICANCE

Because of the high cost of implanting electrodes and monitoring, the invasive EEG for patients with refractory epilepsy is currently not available in the Hungarian national healthcare system. Our study demonstrated that these procedures in Hungary are cost-effective compared with the MM. As a result, the introduction of iEEG interventions to the reimbursement list of the National Health Insurance Fund Administration was initiated.

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

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

Patient phenotypes and clinical outcomes in invasive monitoring for epilepsy: An individual patient data meta-analysis

OBJECTIVE

Invasive monitoring provides valuable clinical information in patients with drug-resistant epilepsy (DRE). However, there is no clear evidence indicating either stereoelectroencephalography (SEEG) or subdural electrodes (SDE) as the optimal method. Our goal was to examine differences in postresection seizure freedom rates between SEEG- and SDE-informed resective epilepsy surgeries. Additionally, we aimed to determine potential clinical indicators for SEEG or SDE monitoring in patients with drug-resistant epilepsy.

METHODS

A systematic literature review was performed in which we searched for primary articles using keywords such as "electroencephalography", "intracranial grid", and "epilepsy." Only studies containing individual patient data (IPD) were included for analysis. A one-stage IPD meta-analysis was performed to determine differences in rates of seizure freedom (International League Against Epilepsy (ILAE) guidelines and Engel classification) and resection status between SEEG and SDE patients. A Cox proportional-hazards regression was performed to determine the effect of time on seizure freedom status. Additionally, a principal component analysis was performed to investigate primary drivers of variance between these two groups.

RESULTS

This IPD meta-analysis compared differences between SEEG and SDE invasive monitoring techniques in 595 patients from 33 studies. Our results demonstrate that while there was no difference in seizure freedom rates regardless of resection (p = 0.0565), SEEG was associated with a lower rate of resection compared with SDE (82.00% SEEG, 92.74% SDE, p = 0.0002). Additionally, while SDE was associated with a higher rate of postresection seizure freedom (54.04% SEEG, 64.32% SDE, p = 0.0247), the difference between seizure freedom rates following SEEG- or SDE-informed resection decreased with long-term follow-up. A principal component analysis showed that cases resulting in SEEG were associated with lower risk of morbidity than SDE cases, which were strongly collinear with multiple subpial transections, anterior temporal lobectomy, amygdalectomy, and hippocampectomy.

SIGNIFICANCE

In this IPD meta-analysis of SEEG and SDE invasive monitoring techniques, SEEG and SDE were associated with similar rates of seizure freedom at latest follow-up. The former was associated with lower rates of resection. Furthermore, the clinical phenotypes of patients undergoing SEEG monitoring was associated with lower rates of complications. Future long-term prospective registries of IPD are promising options for clarifying the differences in these intracranial monitoring techniques as well as the unique patient phenotypes that may be associated with their indication.

Craniotomy Size for Subdural Grid Electrode Placement in Invasive Epilepsy Diagnostics

BACKGROUND

Traditionally, for subdural grid electrode placement, large craniotomies have been applied for optimal electrode placement. Nowadays, microneurosurgeons prefer patient-tailored minimally invasive approaches. Absolute figures on craniotomy size have never been reported. To elucidate the craniotomy size necessary for successful diagnostics, we reviewed our single-center experience.

METHODS

Within 3 years, 58 patients with focal epilepsies underwent subdural grid implantation using patient-tailored navigation-based craniotomies. Craniotomy sizes were measured retrospectively. The number of electrodes and the feasibility of the resection were evaluated. Sixteen historical patients served as controls.

RESULTS

In all 58 patients, subdural electrodes were implanted as planned through tailored craniotomies. The mean craniotomy size was 28 ± 15 cm2 via which 55 ± 16 electrodes were implanted. In temporal lobe diagnostics, even smaller craniotomies were applied (21 ± 11 cm2). Craniotomies were significantly smaller than in historical controls (65 ± 23 cm2, p < 0.05), while the mean number of electrodes was comparable. The mean operation time was shorter and complications were reduced in tailored craniotomies.

CONCLUSION

Craniotomy size for subdural electrode implantation is controversial. Some surgeons favor large craniotomies, while others strive for minimally invasive approaches. For the first time, we measured the actual craniotomy size for subdural grid electrode implantation. All procedures were straightforward. We therefore advocate for patient-tailored minimally invasive approaches - standard in modern microneurosurgery - in epilepsy surgery as well.

Stereoelectroencephalography in epilepsy, cognitive neurophysiology, and psychiatric disease: safety, efficacy, and place in therapy

For patients with drug-resistant epilepsy, surgical intervention may be an effective treatment option if the epileptogenic zone (EZ) can be well localized. Subdural strip and grid electrode (SDE) implantations have long been used as the mainstay of intracranial seizure localization in the United States. Stereoelectroencephalography (SEEG) is an alternative approach in which depth electrodes are placed through percutaneous drill holes to stereotactically defined coordinates in the brain. Long used in certain centers in Europe, SEEG is gaining wider popularity in North America, bolstered by the advent of stereotactic robotic assistance and mounting evidence of safety, without the need for catheter-based angiography. Rates of clinically significant hemorrhage, infection, and other complications appear lower with SEEG than with SDE implants. SEEG also avoids unnecessary craniotomies when seizures are localized to unresectable eloquent cortex, found to be multifocal or nonfocal, or ultimately treated with stereotactic procedures such as laser interstitial thermal therapy (LITT), radiofrequency thermocoagulation (RF-TC), responsive neurostimulation (RNS), or deep brain stimulation (DBS). While SDE allows for excellent localization and functional mapping on the cortical surface, SEEG offers a less invasive option for sampling disparate brain areas, bilateral investigations, and deep or medial targets. SEEG has shown efficacy for seizure localization in the temporal lobe, the insula, lesional and nonlesional extra-temporal epilepsy, hypothalamic hamartomas, periventricular nodular heterotopias, and patients who have had prior craniotomies for resections or grids. SEEG offers a valuable opportunity for cognitive neurophysiology research and may have an important role in the study of dysfunctional networks in psychiatric disease and understanding the effects of neuromodulation.

Transcranial direct current stimulation (tDCS) for upper limb rehabilitation after stroke: future directions

Transcranial Direct Current Stimulation (tDCS) is a potentially useful tool to improve upper limb rehabilitation outcomes after stroke, although its effects in this regard have shown to be limited so far. Additional increases in effectiveness of tDCS in upper limb rehabilitation after stroke may for example be achieved by (1) applying a more focal stimulation approach like high definition tDCS (HD-tDCS), (2) involving functional imaging techniques during stimulation to identify target areas more exactly, (3) applying tDCS during Electroencephalography (EEG) (EEG-tDCS), (4) focusing on an effective upper limb rehabilitation strategy as an effective base treatment after stroke. Perhaps going even beyond the application of tDCS and applying alternative stimulation techniques such as transcranial Alternating Current Stimulation (tACS) or transcranial Random Noise Stimulation (tRNS) will further increase effectiveness of upper limb rehabilitation after stroke.

Methodology, outcome, safety and in vivo accuracy in traditional frame-based stereoelectroencephalography

Background

Stereoelectroencephalography (SEEG) is an established diagnostic technique for the localization of the epileptogenic zone in drug-resistant epilepsy. In vivo accuracy of SEEG electrode positioning is of paramount importance since higher accuracy may lead to more precise resective surgery, better seizure outcome and reduction of complications.

Objective

To describe experiences with the SEEG technique in our comprehensive epilepsy center, to illustrate surgical methodology, to evaluate in vivo application accuracy and to consider the diagnostic yield of SEEG implantations.

Methods

All patients who underwent SEEG implantations between September 2008 and April 2016 were analyzed. Planned electrode trajectories were compared with post-implantation trajectories after fusion of pre- and postoperative imaging. Quantitative analysis of deviation using Euclidean distance and directional errors was performed. Explanatory variables for electrode accuracy were analyzed using linear regression modeling. The surgical methodology, procedure-related complications and diagnostic yield were reported.

Results

Seventy-six implantations were performed in 71 patients, and a total of 902 electrodes were implanted. Median entry and target point deviations were 1.54 mm and 2.93 mm. Several factors that predicted entry and target point accuracy were identified. The rate of major complications was 2.6%. SEEG led to surgical therapy of various modalities in 53 patients (69.7%).

Conclusions

This study demonstrated that entry and target point localization errors can be predicted by linear regression models, which can aid in identification of high-risk electrode trajectories and further enhancement of accuracy. SEEG is a reliable technique, as demonstrated by the high accuracy of conventional frame-based implantation methodology and the good diagnostic yield.

The evolution of endovascular electroencephalography: historical perspective and future applications

Current standard practice requires an invasive approach to the recording of electroencephalography (EEG) for epilepsy surgery, deep brain stimulation (DBS), and brain-machine interfaces (BMIs). The development of endovascular techniques offers a minimally invasive route to recording EEG from deep brain structures. This historical perspective aims to describe the technical progress in endovascular EEG by reviewing the first endovascular recordings made using a wire electrode, which was followed by the development of nanowire and catheter recordings and, finally, the most recent progress in stent-electrode recordings. The technical progress in device technology over time and the development of the ability to record chronic intravenous EEG from electrode arrays is described. Future applications for the use of endovascular EEG in the preoperative and operative management of epilepsy surgery are then discussed, followed by the possibility of the technique's future application in minimally invasive operative approaches to DBS and BMI.

[Stereoelectroencephalography by using O-Arm® and Vertek® passive articulated arm: Technical note and experience of an epilepsy referral centre]

OBJECTIVE

To report a novel, accurate, and safe technique for deep brain electrode implantation to register brain electrical activity or SEEG, using frameless stereotaxy, neuronavigation assisted, and intraoperative CT-guided O-Arm^® and the Vertek^® articulated passive arm.

MATERIAL AND METHODS

All patients implanted by this technique in Barcelona Hospital Clinic were included. A prospective evaluation was made of the accuracy of the technique, as well as complications, surgical time, length of stay, and short-term outcomes.

RESULTS

The study included 10 patients that underwent this procedure. The mean age was 38 years, and 60% were women. A mean of 6.9 (3-10) electrodes/patient, with a total of 69 electrodes, were implanted. The mean time for implantation was 34.7minutes per electrode. The mean distance between the planned target and the final target was 1.39 millimetres (0.95-1.7). There were no surgically derived complications. The epileptogenic zone was determined in 6 cases (60%). Surgical resection was performed in 5 cases (50%), with thermocoagulation in 3 (30%) cases, and in 2 cases (20%) there was no treatment. At a six-month follow-up of the 8 treated cases, 37.5% were ELAI I, 12.5% ELAI III, 25% ELAI IV, and 25% ELAI V.

CONCLUSIONS

The implantation of deep brain electrodes for SEEG by using intraoperative CT O-Arm^® and the Vertek^® articulated passive arm is a safe and effective technique with adequate accuracy.

Single and paired-pulse electrical stimulation during invasive EEG recordings

Invasive EEG recordings are frequently required during the presurgical exploration of patients with drug-resistant focal epilepsy in order to clarify the epileptic zone location. Intracranial direct electrical stimulations (DES) induce EEG and/or clinical responses that participate in this evaluation. Clinical DES protocols (1Hz and/or 50Hz) trigger massive cortical activation that can elicit seizures, after-discharges or complex clinical signs. In contrast, low-energy (<1Hz) protocols activate more localized cortical regions using single-pulse electrical stimulations (SPES). SPES can elicit two main types of responses. Cortico-cortical evoked potentials (CCEPs) correspond to highly consistent early responses, appearing before 100ms after stimulation, with fixed latency; they are considered physiological and assess the effective connectivity between the recorded regions. Late responses appear after 100ms; they are rare, inconsistent with variable latency and are suggestive of an underlying epileptogenic cortex. Paired-pulse stimulation paradigm associates a conditioning and a test stimulation to induce intracortical inhibition or facilitation by modifying the response amplitude. Largely used in transcranial magnetic stimulation, it has rarely been applied to CCEP although the mechanisms put in place seem highly similar. Low frequency intracerebral stimulations allow analysing brain connectivity and cortical excitability with a high temporal and spatial resolution. The development of new stimulation protocols and the combination with imaging or statistical techniques recently offered promising results.