Placement Of Intracranial Electrodes Research Articles

835 Rapid Prototyping, Digital Sculpting, and Computer Aided Design for Point of Care 3D Printed Stereo EEG Models

INTRODUCTION: Part of the workup for surgical management of epilepsy is stereotactic placement of intracranial depth electrodes to better understand the origin and network pattern of spread of seizures. To facilitate surgical decision making, epilepsy team discussion, and patient/family communication, a workflow was developed to create 3D printed models of sEEG patient brains and electrode locations which could be invaluable in explaining EEG results and surgical options. METHODS: Pre-op MRI and post-implantation CT scans of a sEEG case were imported and merged using 3D Slicer, a free and open-source software package for advanced medical imaging research.The CT was segmented to include only the high-density metallic electrodes. These 3D models were exported into Autodesk Fusion 360, a computer-aided design (CAD) program, where electrode models were designed based on their location on the CT scan. These models were exported to Maxon Zbrush to be cleaned and re-meshed to make the model easier to sculpt and manipulate.The electrode objects were used as cutting tools to create holes in the brain model. Finally, the relevant portion of the brain (right temporal lobe and surrounding regions) and electrodes were exported for 3D printing. The final models were 3D printed on a FormLabs Form 3 stereolithography (SLA) printer using clear resin for the brain and flexible grey resin for the electrodes. RESULTS: CONCLUSIONS: A workflow was devised to print anatomic models of brains implanted with electrodes for seizure monitoring in 2-3 days utilizing software from multiple disciplines including medical imaging, CAD/engineering, and 3D sculpting used in the film and video game industries. Future models will include further anatomical definition with more advanced 3D sculpting and printing techniques.

Distinct connectivity patterns in human medial parietal cortices: Evidence from standardized connectivity map using cortico-cortical evoked potential

The medial parietal cortices are components of the default mode network (DMN), which are active in the resting state. The medial parietal cortices include the precuneus and the dorsal posterior cingulate cortex (dPCC). Few studies have mentioned differences in the connectivity in the medial parietal cortices, and these differences have not yet been precisely elucidated. Electrophysiological connectivity is essential for understanding cortical function or functional differences. Since little is known about electrophysiological connections from the medial parietal cortices in humans, we evaluated distinct connectivity patterns in the medial parietal cortices by constructing a standardized connectivity map using cortico-cortical evoked potential (CCEP). This study included nine patients with partial epilepsy or a brain tumor who underwent chronic intracranial electrode placement covering the medial parietal cortices. Single-pulse electrical stimuli were delivered to the medial parietal cortices (38 pairs of electrodes). Responses were standardized using the z-score of the baseline activity, and a response density map was constructed in the Montreal Neurological Institutes (MNI) space. The precuneus tended to connect with the inferior parietal lobule (IPL), the occipital cortex, superior parietal lobule (SPL), and the dorsal premotor area (PMd) (the four most active regions, in descending order), while the dPCC tended to connect to the middle cingulate cortex, SPL, precuneus, and IPL. The connectivity pattern differs significantly between the precuneus and dPCC stimulation (p<0.05). Regarding each part of the medial parietal cortices, the distributions of parts of CCEP responses resembled those of the functional connectivity database. Based on how the dPCC was connected to the medial frontal area, SPL, and IPL, its connectivity pattern could not be explained by DMN alone, but suggested a mixture of DMN and the frontoparietal cognitive network. These findings improve our understanding of the connectivity profile within the medial parietal cortices. The electrophysiological connectivity is the basis of propagation of electrical activities in patients with epilepsy. In addition, it helps us to better understand the epileptic network arising from the medial parietal cortices.

Frequency band coupling with high-frequency activities in tonic-clonic seizures shifts from θ to δ band

ObjectiveTo clarify variations in the relationship between high-frequency activities (HFAs) and low-frequency bands from the tonic to the clonic phase in focal to bilateral tonic-clonic seizures (FBTCS), using phase-amplitude coupling. MethodsThis retrospective study enrolled six patients with drug-resistant focal epilepsy who underwent intracranial electrode placement at Osaka University Hospital (July 2018–July 2019). We recorded 11 FBTCS. The synchronization index (SI) and receiver-operating characteristic (ROC) analysis were used to analyze the coupling between HFA amplitude (80–250 Hz) and lower frequencies phase. ResultsIn the tonic phase, the θ (4–8 Hz)-HFA coupling peaked, and the HFA power occurred at baseline (0 μV) of θ oscillations. In contrast, in the clonic phase, the δ (2–4 Hz)-HFA coupling peaked, and the HFA power occurred at the trough of δ oscillations. ROC analysis indicated that the δ-HFA SI discriminated well the clonic from the tonic phase. ConclusionsThe main low-frequency band modulating the HFA shifted from the θ band in the tonic phase to the δ band in the clonic phase. SignificanceNeurophysiological key frequency bands were implied to be the θ band and δ band in tonic and clonic seizures, respectively, which improves our understanding of FBTCS.

Phase-amplitude coupling between infraslow and high-frequency activities well discriminates between the preictal and interictal states

Infraslow activity (ISA) and high-frequency activity (HFA) are key biomarkers for studying epileptic seizures. We aimed to elucidate the relationship between ISA and HFA around seizure onset. We enrolled seven patients with drug-resistant focal epilepsy who underwent intracranial electrode placement. We comparatively analyzed the ISA, HFA, and ISA-HFA phase-amplitude coupling (PAC) in the seizure onset zone (SOZ) or non-SOZ (nSOZ) in the interictal, preictal, and ictal states. We recorded 15 seizures. HFA and ISA were larger in the ictal states than in the interictal or preictal state. During seizures, the HFA and ISA of the SOZ were larger and occurred earlier than those of nSOZ. In the preictal state, the ISA-HFA PAC of the SOZ was larger than that of the interictal state, and it began increasing at approximately 87 s before the seizure onset. The receiver-operating characteristic curve revealed that the ISA-HFA PAC of the SOZ showed the highest discrimination performance in the preictal and interictal states, with an area under the curve of 0.926. This study demonstrated the novel insight that ISA-HFA PAC increases before the onset of seizures. Our findings indicate that ISA-HFA PAC could be a useful biomarker for discriminating between the preictal and interictal states.

The Changing Nature of Epilepsy Surgery: A Retrospective Review of Practice Profiles

Recent literature documents a trend of gradual decline in temporal lobe (resective) epilepsy surgery over the past decade. Amongst these, a large scale, comprehensive survey done in selected European, Australian and American centres documents trends of resective temporal epilepsy surgery across two decades. Montreal Neurological Institute has been the leading epilepsy surgery centre for more than 50 years now. It has been at the forefront of investigating and managing epilepsy in Canada. We have looked into the trends of epilepsy surgery in our institute in the past 44 years. The records of all adult epilepsy surgery procedures (excluding reoperations) performed by the senior authors were analysed from 1971 to 2015. Data retrieved for analysis included type of surgery (intracranial recording, resective, and neuromodulatory) and the specific surgical target for resection. Procedures were grouped into temporal resective, extratemporal (ET) resective and placement of intracranial electrodes (stereotactic electroencephalogram (SEEG)). A total of 2,078 new procedures were performed from 1971 to 2015 at the Montreal Neurological Institute. Temporal procedures constituted the bulk of the proportion of all procedures each year and the entire study period. SEEG group shows linear increase in the number of cases over the years catching up with the total number of temporal procedures. Our study involving a homogenous dataset spanning nearly 50 years shows a decline in temporal lobe surgeries and an increase in intracranial investigations despite the class I evidence of its effectiveness. This corroborates the trends in epilepsy surgery practice profiles in tertiary centres of developed countries.

Robot-assisted stereoelectroencephalography electrode placement in twenty-three pediatric patients: a high-resolution analysis of individual lead placement time and accuracy at a single institution.

We describe a detailed evaluation of predictors associated with individual lead placement efficiency and accuracy for 261 stereoelectroencephalography (sEEG) electrodes placed for epilepsy monitoring in twenty-three children at our institution. Intra- and post-operative data was used to generate a linear mixed model to investigate predictors associated with three outcomes (lead placement time, lead entry error, lead target error) while accounting for correlated observations from the same patients. Lead placement time was measured using electronic time-stamp records stored by the ROSA software for each individual electrode; entry and target site accuracy was measured using postoperative stereotactic CT images fused with preoperative electrode trajectory planning images on the ROSA computer software. Predictors were selected from a list of variables that included patient demographics, laterality of leads, anatomic location of lead, skull thickness, bolt cap device used, and lead sequence number. Twenty-three patients (11 female, 48%) of mean age 11.7 (± 6.1) years underwent placement of intracranial sEEG electrodes (median 11 electrodes) at our institution over a period of 1 year. There were no associated infections, hemorrhages, or other adverse events, and successful seizure capture was obtained inall monitored patients. The mean placement time for individual electrodes across all patients was 6.56 (± 3.5) min; mean target accuracy was 4.5 (± 3.5) mm. Lesional electrodes were associated with 25.7% (95% CI: 6.7-40.9%, p = 0.02) smaller target point errors. Larger skull thickness was associated with larger error: for every 1-mm increase in skull thickness, there was a 4.3% (95% CI: 1.2-7.5%, p = 0.007) increase in target error. Bilateral lead placement was associated with 26.0% (95% CI: 9.9-44.5%, p = 0.002) longer lead placement time. The relationship between placement time and lead sequence number was nonlinear: it decreased consistently for the first 4 electrodes, and became less pronounced thereafter. Variation in sEEG electrode placement efficiency and accuracy can be explained by phenomena both within and outside of operator control. It is important to keep in mind the factors that can lead to better or worse lead placement efficiency and/or accuracy in order to maximize patient safety while maintaining the standard of care.

Combining 3D-printing Technology with Pre-operative Sterotactic Planning for Placement of Intracranial Depth Electrodes for Improved Patient Safety and Operative Efficiency: An Institutional Experience (2558)

Combining 3D-printing Technology with Pre-operative Sterotactic Planning for Placement of Intracranial Depth Electrodes for Improved Patient Safety and Operative Efficiency: An Institutional Experience (2558)

The sensitivity of network statistics to incomplete electrode sampling on intracranial EEG.

Network neuroscience applied to epilepsy holds promise to map pathological networks, localize seizure generators, and inform targeted interventions to control seizures. However, incomplete sampling of the epileptic brain because of sparse placement of intracranial electrodes may affect model results. In this study, we evaluate the sensitivity of several published network measures to incomplete spatial sampling and propose an algorithm using network subsampling to determine confidence in model results. We retrospectively evaluated intracranial EEG data from 28 patients implanted with grid, strip, and depth electrodes during evaluation for epilepsy surgery. We recalculated global and local network metrics after randomly and systematically removing subsets of intracranial EEG electrode contacts. We found that sensitivity to incomplete sampling varied significantly across network metrics. This sensitivity was largely independent of whether seizure onset zone contacts were targeted or spared from removal. We present an algorithm using random subsampling to compute patient-specific confidence intervals for network localizations. Our findings highlight the difference in robustness between commonly used network metrics and provide tools to assess confidence in intracranial network localization. We present these techniques as an important step toward translating personalized network models of seizures into rigorous, quantitative approaches to invasive therapy.

Using 3D-Printed Mesh-Like Brain Cortex with Deep Structures for Planning Intracranial EEG Electrode Placement.

Surgical evaluation of medically refractory epilepsy frequently necessitates implantation of multiple intracranial electrodes for the identification of the seizure focus. Knowledge of the individual brain's surface anatomy and deep structures is crucial for planning the electrode implantation. We present a novel method of 3D printing a brain that allows for the simulation of placement of all types of intracranial electrodes. We used a DICOM dataset of a T1-weighted 3D-FSPGR brain MRI from one subject. The segmentation tools of Materialise Mimics 21.0 were used to remove the osseous anatomy from brain parenchyma. Materialise 3-matic 13.0 was then utilized in order to transform the cortex of the segmented brain parenchyma into a mesh-like surface. Using 3-matic tools, the model was modified to incorporate deep brain structures and create an opening in the medial aspect. The final model was then 3D printed as a cerebral hemisphere with nylon material using selective laser sintering technology. The final model was light and durable and reflected accurate details of the surface anatomy and some deep structures. Additionally, standard surgical depth electrodes could be passed through the model to reach deep structures without damaging the model. This novel 3D-printed brain model provides a unique combination of visualizing both the surface anatomy and deep structures through the mesh-like surface while allowing repeated needle insertions. This relatively low-cost technique can be implemented for interdisciplinary preprocedural planning in patients requiring intracranial EEG monitoring and for any intervention that requires needle insertion into a solid organ with unique anatomy and internal targets.

Standard Free Versus Osteoplastic Craniotomy: Assessment of Complication Rates During Intracranial Electroencephalogram Electrode Placement for Seizure Localization

Patients with medically intractable epilepsy often undergo sequential surgeries and are therefore exposed to an elevated risk for infection, resulting in unanticipated returns to the operating room. The goal of our study was to determine whether use of an osteoplastic bone flap technique would reduce the infection rate in these patients. A single-institution, retrospective chart review of patients with medically intractable epilepsy for grid placement was performed. Univariate analyses and linear regression were used to assess primary outcomes, including infection and hematomas requiring surgical evacuation. Secondary outcomes included duration of treatment and other, unanticipated surgeries. A total of 199 patients were identified, 56 (28%) with osteoplastic flaps. Standard free flaps were associated with an increased rate of infection at the craniotomy site (n= 24, 17%, vs. 0, 0%, P= 0.003), whereas osteoplastic flaps were associated with more returns to operating room for hematoma evacuation (n= 5, 9% vs. 3.2%, P= 0.024). Overall, the rate of return to operating room for unanticipated surgeries was similar, but infectious complications prolonged the duration of treatment (median: 17 days vs. 2 days, χ2= 13.97, P < 0.001). Osteoplastic bone flaps markedly decreased the risk of craniotomy infections compared with free flaps in patients undergoing sequential surgeries. This decrease is offset, however, by an increase in intracranial hematoma requiring return to the operating room. Infection appeared to be a more significant complication as it was associated with increased duration of treatment. The osteoplastic technique is especially appealing in those patients likely to undergo multiple surgeries in short succession.

Overview of Seizure and Epilepsy Syndromes and Their Multidisciplinary Management

Abnormal hyperexcitable electrical discharges of the cerebral cortex lead to the disturbance between the inhibitory and excitatory balance of the neural network. Seizure is caused by four main mechanisms, including metabolic, structural, inflammatory, and infectious mechanisms. Seizures are classified as partial and generalized based on the isolation in a specific area in one brain hemisphere or passing through the nerve fibers and spreading to the other hemisphere as well. Epilepsy is defined as the occurrence of more than two unprovoked and unpredicted repeated seizures. Epilepsy affects more than three million individuals in the United States and approximately 50 million individuals worldwide. Epilepsy may be of an unknown origin, while it could also be associated with certain syndromes. General and specific approaches to seizure treatment encompass a wide range of factors. The general approach should be focused on reassurance and raising the awareness of the patients and their family, and the specific treatment is focused on utilizing pharmacological and surgical approaches. In general, the surgical approaches used for medication-refractory seizures are both palliative and curative, showing promising results if the epileptogenic area is localized using a multidisciplinary approach via live video-electroencephalography monitoring or direct intracranial electrode placement. In addition, the utilization of live modern imaging modalities coupled with surgical approaches could enhance the success rate of the treatment and increase the seizure-free duration.

Outcome analysis of surgical resections in patients with refractory epilepsy—A review of 15-year experience at a single center

Objective To summarize the epileptogenic localizations, pathological findings and long-term surgical outcomes of patients with refractory epilepsy at a single center during past 15 years. Methods A total of 2 424 patients who underwent epilepsy surgeries at Department of Functional Neurosurgery between April 2001 and December 2016 were included in this retrospective study. The traits of epileptogenic localization were analyzed. Outcomes of all patients who were followed up longer than 1 year post surgeries were studied in two stages, and the rate of seizure free was calculated. Results Among all 2 424 patients, 1 299 (53.6%) had obvious lesions on MRI. There were 1 007 (41.5%) patients who underwent intracranial electrode placement and 65.5% of those had no definite lesions on MRI. There were 1 030 (42.5%) cases who were diagnosed as temporal lobe epilepsy (TLE) and 1 394 (57.5%) diagnosed as extratemporal lobe epilepsy (ETLE). The common pathological types included focal cortical dysplasia (37.5%, 909), mesial temporal sclerosis (17.7%, 429), ulegyria (15.7%, 381) and low grade tumor (9.2%, 223). There was a double pathological change in 303 (12.5%) patients. A total of 1 424 (59.0%) patients were followed up for more than 1 year post surgery. At the first stage of follow-up (April 2001 to July 2012), 846 patients completed follow-up lasting at least 1 year. The seizure-free rate was 64.7% (547/846) at 1 year, 52.5% (241/459) at 3 years and 49.6% (119/240) at 5 years post surgery. For the patients with TLE, the seizure-free rate was 57.9% (210/363) at 1 year, 57.8% (108/187) at 3 years and 56.3% (58/103) at 5 years post surgery. For the patients with ETLE, the seizure-free rate was 59.4% (287/483) at 1 year, 47.8% (130/272) at 3 years and 46.7% (64/137) at 5 years post operation. At the second stage of follow-up (August 2012 to September 2015), 578 patients completed follow-up lasting at least 1 year. The seizure-free rate was 64.7% (374/578) at 1 year and 57.3% (133/232) at 3 years post surgery. For the patients with TLE, the seizure-free rate was 71.4% (187/262) at 1 year and 66.4% (64/95) at 3 years post operation. For patients with ETLE, the seizure-free rate was 59.5% (188/316) and 51.1% (70/137) at 1 year and 3 years post operation respectively. However, the difference in the seizure free rate was significant only at the first year post surgery in the patients with TLE between the 2 stages (57.9% vs. 71.4%, P=0.001), and there was no significant difference afterwards. Conclusions Long-term intracranial recording seems to be indispensable for identification of epileptogenic focus for some patients. Although surgical efficacy might decrease to some extent with extension of postoperative time, surgical treatment is beneficial and postoperative outcome is relatively stable for patients with either temporal or extratemporal epilepsy. Key words: Epilepsy; Neurosurgical procedures; Treatment outcome; Temporal lobe epilepsy; Extratemporal lobe epilepsy

Intracranial Electrode Placement for Seizures Before Temporal Lobectomy: A Risk-Benefit Analysis

Anterior temporal lobectomy (ATL) is the most common surgical procedure for refractory temporal lobe epilepsy. When scalp electroencephalography cannot adequately identify an epileptogenic site, electrode implantation may be used to monitor epileptic activity and localize a target focus before surgical resection. Whether the advantage of improved seizure localization justifies the added risk of electrode placement remains unclear. : The present study uses an international surgical database to explore whether a 2wo-stage approach, electrode implant followed by ATL, has a reasonable safety profile and is clinically worthwhile versus ATL alone. Data from the American College of Surgeons National Surgical Quality Improvement Program for 2005 to 2016 were queried to identify patients undergoing ATL or electrode implant for epilepsy. The 30-day postoperative outcomes were analyzed for the electrode implant and ATL groups, and individual and combined risk profiles were determined. Patients undergoing electrode implant followed by ATL had a predicted reoperation rate of 7.6%, readmission rate of 14.6%, and a 30-day mortality rate of 1.2%. The combined rate of patients having ≥1 medical complication for 2-staged procedures was higher, at 14.7%. The most common complications encountered were urinary tract infection (2.7%) and sepsis (2.7%). Intracranial electrode placement increases the risk of complications when added to ATL. The severity of complications from electrode placement are mild, however, and as intracranial electrode recording provides a potentially large reduction in the surgical failure risk, electrode placement may be advisable for all but the most convincing seizure foci.

Structural and effective connectivity in focal epilepsy.

Patients with medically-refractory focal epilepsy may be candidates for neurosurgery and some may require placement of intracranial EEG electrodes to localise seizure onset. Assessing cerebral responses to single pulse electrical stimulation (SPES) may give diagnostically useful data. SPES produces cortico-cortical evoked potentials (CCEPs), which infer effective brain connectivity. Diffusion-weighted images and tractography may be used to estimate structural brain connectivity. This combination provides the opportunity to observe seizure onset and its propagation throughout the brain, spreading contiguously along the cortex explored with electrodes, or non-contiguously. We analysed CCEPs and diffusion tractography in seven focal epilepsy patients and reconstructed the effective and structural brain networks. We aimed to assess the inter-modal similarity of the networks at a large scale across the cortex, the effective and structural connectivity of the ictal-onset zone, and investigate potential mechanisms of non-contiguous seizure spread. We found a significant overlap between structural and effective networks. Effective network CCEP amplitude, baseline variation, and outward connectivity was higher at ictal-onset zones, while structural connection strength within the ictal-onset zone tended to be higher. These findings support the concept of hyperexcitable cortex being associated with seizure generation. The high prevalence of structural and effective connections from the ictal-onset zone to sites of non-contiguous spread suggests that macroscopic structural and effective connections are plausible routes for non-contiguous seizure spread.

Refractory Epilepsy: The Role of Positron Emission Tomography.

Presurgical localization of the epileptogenic focus is critical to successful surgery. Traditionally, localization of the epileptogenic focus depends on seizure semiology, scalp video-electroencephalography (vEEG), magnetic resonance imaging (MRI), neuropsychological assessment, and, when needed, intracranial EEG (iEEG). We aimed to explore the role of positron emission tomography (PET) in the presurgical evaluation of patients with refractory epilepsy. A retrospective review was conducted on patients from London Health Sciences Centre (London, Ontario) with refractory epilepsy who underwent PET from September of 2011 to April of 2016. The accuracy of epileptogenic focus localization was compared between different investigative modalities (MRI, vEEG, iEEG, PET), and the outcomes were documented, including seizure freedom after surgical resection, improvement of seizure frequency, guidance for further investigations, and exclusion of patients from further evaluation. Patients who underwent surgery were followed up at 3 months and onward. We identified 62 patients with refractory epilepsy who underwent PET. The mean age was 34 years (range=20-68). A total of 36 had concordant PET and vEEG findings: 6 had surgical resection and either became seizure-free (29.4%) or had improvement in seizure frequency (5.9%) at 3 months; 11 had surgical resection and either became seizure-free (29.4%) or had improvement in seizure frequency (35.3%) at 3 months, but required iEEG for final verification. PET has an important role in presurgical evaluation of patients with refractory epilepsy. It may allow resection of the epileptogenic focus without the need for iEEG, guiding intracranial electrode placement for further localization of the epileptogenic focus, or exclusion of patients from further evaluation.

Bone flap elevation for intracranial EEG monitoring: technical note.

Intracranial electroencephalography (iEEG) provides invaluable information in determining seizure focus and spread due to its high spatial and temporal resolution, which are not afforded by noninvasive studies. Electrodes of various types (e.g., grid, strip, and depth electrodes) and configurations are often used for optimum coverage of suspected areas of seizure onset and propagation. Given the fixed intracranial volume and added mass effect from placement of cortical electrodes, brain edema and postoperative deficits can occur. The authors describe a simple, inexpensive, and highly effective technique of bone flap replacement using standard titanium plates to expand the intracranial volume and minimize risks of brain compression and intracranial hypertension. Rectangular titanium plates are bent and placed in a way that secures the bone flap in a slightly elevated position relative to the adjacent calvaria during iEEG monitoring. The authors evaluated the degree of bone flap elevation and amount of volume created using this technique in 3 iEEG cases. They then compared these results with the bone flap elevation and volume created using linear titanium plates, a method they had used previously. The use of rectangular plates produced on average 6.6 mm of bone flap elevation, compared with only 1.8 mm of bone flap elevation with the use of linear plates, resulting in a statistically significant 261% increase in bone flap elevation (p ≤ 0.001). The authors suggest that rectangular plates may provide stronger resistance to scalp tension after myocutaneous skin closure compared with the linear plates and that subsidence of the bone flap likely occurred with the use of linear plates. In summary, the described technique utilizing rectangular plates creates significantly increased bone flap elevation compared with a similar method using linear plates, and it may reduce the risk of neurological deficits related to intracranial electrode placement.

Retrospective evaluation and SEEG trajectory analysis for interactive multi-trajectory planner assistant.

Focal epilepsy is a neurological disease that can be surgically treated by removing area of the brain generating the seizures. The stereotactic electroencephalography (SEEG) procedure allows patient brain activity to be recorded in order to localize the onset of seizures through the placement of intracranial electrodes. The planning phase can be cumbersome and very time consuming, and no quantitative information is provided to neurosurgeons regarding the safety and efficacy of their trajectories. In this work, we present a novel architecture specifically designed to ease the SEEG trajectory planning using the 3D Slicer platform as a basis. Trajectories are automatically optimized following criteria like vessel distance and insertion angle. Multi-trajectory optimization and conflict resolution are optimized through a selective brute force approach based on a conflict graph construction. Additionally, electrode-specific optimization constraints can be defined, and an advanced verification module allows neurosurgeons to evaluate the feasibility of the trajectory. A retrospective evaluation was performed using manually planned trajectories on 20 patients: the planning algorithm optimized and improved trajectories in 98% of cases. We were able to resolve and optimize the remaining 2% by applying electrode-specific constraints based on manual planning values. In addition, we found that the global parameters used discards 68% of the manual planned trajectories, even when they represent a safe clinical choice. Our approach improved manual planned trajectories in 98% of cases in terms of quantitative indexes, even when applying more conservative criteria with respect to actual clinical practice. The improved multi-trajectory strategy overcomes the previous work limitations and allows electrode optimization within a tolerable time span.

Automated detection of epileptic ripples in MEG using beamformer-based virtual sensors

Objective. In epilepsy, high-frequency oscillations (HFOs) are expressively linked to the seizure onset zone (SOZ). The detection of HFOs in the noninvasive signals from scalp electroencephalography (EEG) and magnetoencephalography (MEG) is still a challenging task. The aim of this study was to automate the detection of ripples in MEG signals by reducing the high-frequency noise using beamformer-based virtual sensors (VSs) and applying an automatic procedure for exploring the time-frequency content of the detected events. Approach. Two-hundred seconds of MEG signal and simultaneous iEEG were selected from nine patients with refractory epilepsy. A two-stage algorithm was implemented. Firstly, beamforming was applied to the whole head to delimitate the region of interest (ROI) within a coarse grid of MEG-VS. Secondly, a beamformer using a finer grid in the ROI was computed. The automatic detection of ripples was performed using the time-frequency response provided by the Stockwell transform. Performance was evaluated through comparisons with simultaneous iEEG signals. Main results. ROIs were located within the seizure-generating lobes in the nine subjects. Precision and sensitivity values were 79.18% and 68.88%, respectively, by considering iEEG-detected events as benchmarks. A higher number of ripples were detected inside the ROI compared to the same region in the contralateral lobe. Significance. The evaluation of interictal ripples using non-invasive techniques can help in the delimitation of the epileptogenic zone and guide placement of intracranial electrodes. This is the first study that automatically detects ripples in MEG in the time domain located within the clinically expected epileptic area taking into account the time-frequency characteristics of the events through the whole signal spectrum. The algorithm was tested against intracranial recordings, the current gold standard. Further studies should explore this approach to enable the localization of noninvasively recorded HFOs to help during pre-surgical planning and to reduce the need for invasive diagnostics.

Accuracy of intracranial electrode placement for stereoencephalography: A systematic review and meta-analysis.

Stereoencephalography (SEEG) is a procedure in which electrodes are inserted into the brain to help define the epileptogenic zone. This is performed prior to definitive epilepsy surgery in patients with drug-resistant focal epilepsy when noninvasive data are inconclusive. The main risk of the procedure is hemorrhage, which occurs in 1-2% of patients. This may result from inaccurate electrode placement or a planned electrode damaging a blood vessel that was not detected on the preoperative vascular imaging. Proposed techniques include the use of a stereotactic frame, frameless image guidance systems, robotic guidance systems, and customized patient-specific fixtures. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, a structured search of the PubMed, Embase, and Cochrane databases identified studies that involve the following: (1) SEEG placement as part of the presurgical workup in patients with (2) drug-resistant focal epilepsy for which (3) accuracy data have been provided. Three hundred twenty-six publications were retrieved, of which 293 were screened following removal of duplicate and non-English-language studies. Following application of the inclusion and exclusion criteria, 15 studies were included in the qualitative and quantitative synthesis of the meta-analysis. Accuracies for SEEG electrode implantations have been combined using a random-effects analysis and stratified by technique. The published literature regarding accuracy of SEEG implantation techniques is limited. There are no prospective controlled clinical trials comparing different SEEG implantation techniques. Significant systematic heterogeneity exists between the identified studies, preventing any meaningful comparison between techniques. The recent introduction of robotic trajectory guidance systems has been suggested to provide a more accurate method of implantation, but supporting evidence is limited to class 3 only. It is important that new techniques are compared to the previous "gold-standard" through well-designed and methodologically sound studies before they are introduced into widespread clinical practice.

An unexpectedly high rate of revisions and removals in deep brain stimulation surgery: Analysis of multiple databases

IntroductionDeep brain stimulation (DBS) is an established therapy for movement disorders, and is under active investigation for other neurologic and psychiatric indications. While many studies describe outcomes and complications related to stimulation therapies, the majority of these are from large academic centers, and results may differ from those in general neurosurgical practice. MethodsUsing data from both the Centers for Medicare and Medicaid Services (CMS) and the National Surgical Quality Improvement Program (NSQIP), we identified all DBS procedures related to primary placement, revision, or removal of intracranial electrodes. Cases of cortical stimulation and stimulation for epilepsy were excluded. ResultsOver 28,000 cases of DBS electrode placement, revision, and removal were identified during the years 2004–2013. In the Medicare dataset, 15.2% and of these procedures were for intracranial electrode revision or removal, compared to 34.0% in the NSQIP dataset. In NSQIP, significant predictors of revision and removal were decreased age (odds ratio (OR) of 0.96; 95% CI: 0.94, 0.98) and higher ASA classification (OR 2.41; 95% CI: 1.22, 4.75). Up to 48.5% of revisions may have been due to improper targeting or lack of therapeutic effect. ConclusionData from multiple North American databases suggest that intracranial neurostimulation therapies have a rate of revision and removal higher than previously reported, between 15.2 and 34.0%. While there are many limitations to registry-based studies, there is a clear need to better track and understand the true prevalence and nature of such failures as they occur in the wider surgical community.