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At the London Health Sciences Centre Epilepsy Program, stereotactically implanted depth electrodes have largely replaced subdural electrodes in the presurgical investigation of patients with drug-resistant epilepsy over the past 4 years. The rationale for this paradigm shift was more experience with, and improved surgical techniques for, stereoelectroencephalography, a possible lower-risk profile for depth electrodes, better patient tolerability, shorter operative time, as well as increased recognition of potential surgical targets that are not accessible to subdural electrodes. Assurer un meilleur suivi de l’activité intracrânienne au moyen de l’électroencéphalographie: passer des électrodes sous-durales aux électrodes implantées en profondeur. Au cours des quatre dernières années, au Centre des sciences de la santé de London (Ontario), établissement offrant un programme de traitement de l’épilepsie, des électrodes implantées en profondeur de manière stéréotaxique ont en grande partie remplacé les électrodes sous-durales dans le cas d’examens pré-chirurgicaux menés auprès de patients atteints d’épilepsie réfractaire aux médicaments. Ce changement de paradigme tient à plusieurs facteurs : une plus grande expérience avec les techniques chirurgicales liées à la stéréo-électroencéphalographie, ces dernières ayant été améliorées ; un niveau de risque possiblement moins élevé dans le cas des électrodes en profondeur ; une meilleure tolérance chez les patients ; des temps opératoires plus courts de même que l’identification accrue de cibles chirurgicales potentielles auxquelles les électrodes sous-durales n’ont pas accès.

Abstract BACKGROUND The insula is a deep cortical structure that has renewed interest in epilepsy investigation. Invasive EEG recordings of this region have been challenging. Robot-assisted stereotactic electroencephalography has improved feasibility and safety of such procedures. OBJECTIVE To describe technical nuances of three-dimensional (3D) oblique trajectories for insular robot-assisted depth electrode implantation. METHODS Fifty patients who underwent robot-assisted depth electrode implantation between June 2017 and December 2018 were retrospectively analyzed. Insular electrodes were implanted through oblique, orthogonal, or parasagittal trajectories. Type of trajectories, accuracy, number of contacts within insular cortex, imaging, and complication rates were analyzed. Cadaveric and computerized tomography/magnetic resonance imaging 3D reconstructions were used to visualize insular anatomy and the technical implications of oblique trajectories. RESULTS Forty-one patients (98 insular electrodes) were included. Thirty (73.2%) patients had unilateral insular coverage. Average insular electrodes per patient was 2.4. The mean number of contacts was 7.1 (SD ± 2.91) for all trajectories and 8.3 (SD ± 1.51) for oblique insular trajectories. The most frequently used was the oblique trajectory (85 electrodes). Mean entry point error was 1.5 mm (0.2-2.8) and target error was 2.4 mm (0.8-4.0), 2.0 mm (1.1-2.9) for anterior oblique and 2.8 mm (0.8-4.9) for posterior oblique trajectories. There were no complications related to insular electrodes. CONCLUSION Oblique trajectories are the preferred method for insular investigation at our institution, maximizing the number of contacts within insular cortex without traversing through sulci or major CSF fissures. Robot-assisted procedures are safe and efficient. 3D understanding of the insula's unique anatomical features can help the surgeon to improve targeting of this structure.

Abstract BACKGROUND Both stereoelectroencephalography (SEEG) and subdural strip electrodes (SSE) are used for intracranial electroencephalographic recordings in the invasive investigation of patients with drug-resistant epilepsy. OBJECTIVE To compare SEEG and SSE with respect to feasibility, complications, and outcome in this single-center study. METHODS Patient characteristics, periprocedural parameters, complications, and outcome were acquired from a pro- and retrospectively managed databank to compare SEEG and SSE cases. RESULTS A total of 500 intracranial electroencephalographic monitoring cases in 450 patients were analyzed (145 SEEG and 355 SSE). Both groups were of similar age, gender distribution, and duration of epilepsy. Implantation of each SEEG electrode took 13.9 ± 7.6 min (20 ± 12 min for each SSE; P < .01). Radiation exposure to the patient was 4.3 ± 7.7 s to a dose area product of 14.6 ± 27.9 rad*cm2 for SEEG and 9.4 ± 8.9 s with 21 ± 22.4 rad*cm2 for SSE (P < .01). There was no difference in the length of stay (12.2 ± 7.2 and 12 ± 6.3 d). The complication rate was low in both groups. No infections were seen in SEEG cases (2.3% after SSE). The rate of hemorrhage was 2.8% for SEEG and 1.4% for SSE. Surgical outcome was similar. CONCLUSION SEEG allows targeting deeply situated foci with a non-inferior safety profile to SSE and seizure outcome comparable to SSE. Graphical Abstract Graphical Abstract

Ultra-high field magnetic resonance imaging (MRI) provides superior visualization of brain structures compared to lower fields, but images may be prone to severe geometric inhomogeneity. We propose to quantify local geometric distortion at ultra-high fields in in vivo datasets of human subjects scanned at both ultra-high field and lower fields. By using the displacement field derived from nonlinear image registration between images of the same subject, focal areas of spatial uncertainty are quantified. Through group and subject-specific analysis, we were able to identify regions systematically affected by geometric distortion at air-tissue interfaces prone to magnetic susceptibility, where the gradient coil non-linearity occurs in the occipital and suboccipital regions, as well as with distance from image isocenter. The derived displacement maps, quantified in millimeters, can be used to prospectively evaluate subject-specific local spatial uncertainty that should be taken into account in neuroimaging studies, and also for clinical applications like stereotactic neurosurgery where accuracy is critical. Validation with manual fiducial displacement demonstrated excellent correlation and agreement. Our results point to the need for site-specific calibration of geometric inhomogeneity. Our methodology provides a framework to permit prospective evaluation of the effect of MRI sequences, distortion correction techniques, and scanner hardware/software upgrades on geometric distortion. •An automated method for quantifying local geometric distortion in millimeters is described.•Focal areas prone to geometric distortion are identified in an in vivo ultra-high field (7T) dataset.•Our method was validated against gold-standard manual fiducial placement demonstrating excellent correlation and agreement.•Automated displacement maps provide informative details regarding spatial uncertainty that should be accounted for in neuroimaging studies and for clinical applications like stereotactic neurosurgery.

Background: Chronic neuropathic groin pain is a common problem. It can arise following surgery or trauma, or spontaneously as part of various pelvic pain syndromes. A number of different stimulation techniques have been reported in the literature to treat this area, but due to the complex anatomy of the region, it can be difficult to target effectively with paresthesias. Objectives: In this study we report our results treating patients with chronic neuropathic groin, pelvic, and abdominal pain, using spinal cord stimulation and dorsal nerve root stimulation. Study Design: Open label, prospective study that includes all patients treated with a new trial stimulator system at a single center between July 1, 2011, and October 31, 2013. Setting: Academic university neurosurgical pain center, Canada. Methods: Thirty-two patients had trials of spinal cord stimulation and/or dorsal nerve root stimulation in the thoracic or lumbar spine. Patients were evaluated on visual analog scale pain scores, SF-36, and morphine equivalent daily dose. Data were recorded at the pre-implant visit, and 3, 6, and 12 months following permanent implant. Results: The 15 patients who went on to permanent implants had, on average, significant pain reduction and improvements in quality of life at the 12 month follow-up. The majority of patients who were taking opioids at the initial assessment were able to reduce their dose with treatment. Three patients with successful trials were long-term non-responders, of whom 2 had the permanent device removed. Limitations: This study would benefit from a larger sample size that would have adequate power for comparisons between patient subgroups and stimulation techniques. Conclusion: Dorsal nerve root stimulation is an effective long-term treatment for neuropathic groin pain. Key words: Spinal cord stimulation, nerve root stimulation, lumbar, thoracic, neuropathic pain, groin pain, pelvic pain, abdominal pain, neuromodulation, clinical effectiveness

Background: Spinal cord stimulation (SCS) is a well-established treatment for chronic neuropathic pain in the lower limbs. Upper limb pain comprises a significant proportion of neuropathic pain patients, but is often difficult to target specifically and consistently with paresthesias. We hypothesized that the use of dorsal nerve root stimulation (DNRS), as an option along with SCS, would help us better relieve pain in these patients. Methods: All 35 patients trialed with spinal stimulation for upper limb pain between July 1, 2011, and October 31, 2013, were included. We performed permanent implantation in 23/35 patients based on a visual analogue scale pain score decrease of ≥50% during trial stimulation. Results: Both the SCS and DNRS groups had significant improvements in average visual analogue scale pain scores at 12 months compared with baseline, and the majority of patients in both groups obtained ≥50% pain relief. The majority of patients in both groups were able to reduce their opioid use, and on average had improvements in Short Form-36 quality of life scores. Complication rates did not differ significantly between the two groups. Conclusions: Treatment with SCS or DNRS provides meaningful long-term relief of chronic neuropathic pain in the upper limbs. Stimulation de la moelle épinière et de la racine dorsale pour soulager la douleur neurogène des membres supérieurs. Contexte: La stimulation de la moelle épinière (SME) est un traitement de la douleur neurogène chronique des membres inférieurs qui a fait ses preuves. Une proportion importante de patients souffre aussi de douleur neurogène aux membres supérieurs mais il demeure ardu de cibler une telle douleur de façon systématique et spécifique en lien avec des manifestations de paresthésie. Nous avons ainsi formulé l’hypothèse que la stimulation de la racine dorsale, en plus de la SME, pourrait nous aider à mieux soulager la douleur chez ces patients. Méthodes: Tous les 35 patients chez qui on avait effectué, du 1er juillet 2011 au 31 octobre 2013, un traitement de SME des membres supérieurs ont été inclus dans cette étude. Pendant les essais cliniques de stimulation, nous avons soumis 23 patients sur 35 à un traitement continu. En nous fondant sur l’échelle visuelle analogique (ÉVA), nous avons anticipé une réduction de ≥50% du score lié à la douleur. Résultats: Au bout de 12 mois, tant les groupes ayant bénéficié de la SME que ceux ayant bénéficié de la stimulation de la racine dorsale ont obtenu, par rapport à des valeurs de référence, des scores nettement meilleurs en matière d’ÉVA de la douleur. En effet, une majorité de patients des deux groupes a rapporté un soulagement de la douleur de ≥50%. Une majorité d’entre eux a aussi été en mesure de réduire sa consommation d’opiacés et a amélioré son score au test SF-36 (Short Form 36 Health Survey) en matière de qualité de vie. Fait à souligner, il n’y a pas eu de différence notable entre les deux groupes quant aux taux de complication. Conclusions: Tant la SME que la stimulation de la racine dorsale offrent un véritable soulagement à long terme de la douleur neurogène chronique des membres supérieurs.

Electrical stimulation mapping (ESM) is an important tool for the localization of the seizure onset zone (SOZ) in patients with medically resistant epilepsy (MRE). ESM is the gold standard for the identification of eloquent cortex in epilepsy surgery candidates. However, there is no standard protocol outlining how to perform ESM, to obtain the most useful information possible. The objective of this study, after reviewing the literature concerning ESM, is to propose a unifying technique to validate reliable data across different centers. In this manuscript we summarize this technique from its origin to present, and review protocols used in other centers. We also describe a protocol that has been used in our institution, which utilizes depth electrodes. The most common type of ESM uses a “close-loop” system, bipolar and high frequency stimulation (50 Hz). We propose to use a pulse width of 300 µs, current spanning 1–6 mA in depth electrodes and 1–11 mA in subdural-grids. Stimulation time of 5 s maximum and at least 10 s break in between the stimulations. ESM is a useful tool for understanding eloquent cortex as well as the epilepsy network, although there is no clear consensus regarding how it should be performed. •Electrical stimulation mapping (ESM) is a technique used for mapping eloquent cortex and verifies the seizure onset zone.•There is not a standardized protocol across centres•This manuscript describes our local protocol, which is based on many years of experience

Spinal cord stimulation (SCS) is a well-established treatment for chronic neuropathic pain in the lower limbs. However, some patients have pain in distributions that are difficult to target specifically and consistently with SCS. This often involves pain in the groin or upper limbs, or pain limited to a specific dermatome. We hypothesized that dorsal nerve root stimulation (DNRS) would provide similar pain relief for these patients, compared to our results using SCS. In this study we report our experience treating patients with chronic neuropathic pain using SCS and DNRS. Open label, prospective study that includes all patients treated with a new trial stimulator system at a single center between July 1, 2011, and October 31, 2013. Academic university neurosurgical pain center. One hundred thirty-two consecutive patients had trials of spinal stimulation. Seventy-six patients went on to permanent implants, of which 26 received only DNRS, 47 only SCS, and 3 both. The technique was selected based on clinical assessment and intraoperative test stimulation. Other than pain location and diagnosis, the DNRS and SCS groups had similar baseline characteristics. Follow-up is reported at 12 months. Patients were assessed using a visual analogue scale (VAS) for pain, the SF-36 for quality of life, and the morphine equivalent daily dose (MEDD). At 12 months, the average VAS score for the DNRS group had decreased from 7.5 (SD 1.4) to 4.4 (SD 2.6) and 47% of patients with permanent implants achieved > 50% pain reduction. There were improvements in all subscores and component summary scores of the SF-36. The MEDD had been reduced in 55% of the patients with available data. There was no significant difference in complication or revision rates between the 2 groups. Patients were not randomized to treatment groups, and instead were assigned to SCS or DNRS based on what was expected to provide superior pain coverage. There is incomplete follow-up data for some patients due to missed clinic visits. In our study, DNRS provided excellent pain reduction, quality of life improvement, and opioid medication use decreases. We conclude that it is an effective long-term treatment for chronic neuropathic pain.Key words: Spinal cord stimulation, dorsal nerve root stimulation, lumbar, thoracic, cervical, neuropathic pain, neuromodulation, clinical effectiveness, chronic pain, visual analogue scale.

\"Temporal plus\" epilepsy (TPE) is a term that is used when the epileptogenic zone (EZ) extends beyond the boundaries of the temporal lobe. Stereotactic electroencephalography (SEEG) has been essential to identify additional EZs in adjacent structures that might be part of the temporal lobe/limbic network. We present a small case series of temporal plus cases successfully identified by SEEG who were seizure-free after resective surgery. We conducted a retrospective analysis of 156 patients who underwent SEEG in 5 years. Six cases had TPE and underwent anterior temporal lobectomy (ATL) with additional extra-temporal resections. Five cases had a focus on the right hemisphere and one on the left. Three cases were non-lesional and three were lesional. Mean follow-up time since surgery was 2.9 years (SD ± 1.8). Three patients had subdural electrodes investigation prior or in addition to SEEG. All patients underwent standard ATL and additional extra-temporal resections during the same procedure or at a later date. All patients were seizure-free at their last follow-up appointment (Engel Ia = 3; Engel Ib = 2; Engel Ic = 1). Pathology was nonspecific/gliosis for all six cases. TPE might explain some of the failures in temporal lobe epilepsy surgery. We present a small case series of six patients in whom SEEG successfully identified this phenomenon and surgery proved effective.

Abstract Background For intracranial electroencephalographic monitoring, stereotactically implanted depth electrodes are increasingly used at epilepsy centers around the world. Objective To identify pearls and pitfalls from our experience with stereotactic Leksell (Elekta AB, Stockhom, Sweden) frame-based depth electrode implantation. Methods An intraoperative video of the implantation technique was recorded. Results A detailed description and a video on how to implant depth electrodes using the stereotactic Leksell frame is provided. Conclusion Neurosurgeons implanting depth electrodes for intracranial electroencephalographic monitoring might find the technical nuances and caveats described in this technical note useful for their practice.