Publications by authors named "Keith W MacDougall"

24 Publications

  • Page 1 of 1

Long-Term Experience with Occipital and Supraorbital Nerve Stimulation for the Various Headache Disorders-A Retrospective Institutional Case Series of 96 Patients.

World Neurosurg 2021 Apr 24. Epub 2021 Apr 24.

Division of Neurosurgery, Department of Clinical Neurological Sciences, London Health Sciences Centre, University Hospital, London, Ontario, Canada.

Objective: We have provided long-term data on clinically meaningful pain alleviation for drug-refractory headache disorders using occipital (ONS) and supraorbital nerve stimulation (SONS).

Methods: We performed a retrospective review of 96 patients with migraine, cervicogenic headache, cluster headache, neuropathic pain of the scalp, tension-type headache, and new daily persistent headache who had undergone ONS (61.5%), SONS (11.5%), or combined ONS plus SONS (27.1%) trial implantation and definitive implantation from 2007 to 2017. Changes in pain perception over time were monitored using the visual analog scale (VAS) for pain.

Results: The cohort consisted of 60.4% women and 39.6% men, with a mean age of 46.9 ± 11.5 years and pain duration of 14 ± 14.1 years. Of the 96 patients, 65 (67.7%) were treatment responders to a trial (≥30% amelioration in the average or maximum VAS score for pain and/or number of headache days) that had lasted 22.5 ± 8.8 days. The reduction in their average VAS score for pain was to 37% ± 24.4% of baseline compared with 99.1% ± 24.1% of baseline for those without a response (P < 0.01). Of the 56 patients who had undergone implantation and had long-term follow-up data available for ≤10 years, 32 (57.1%) reported a ≥50% reduction in their average VAS score for pain. Four patients (6.5%) had requested hardware explantation. Stage II complications included 1 infection (1.6%) and 6 electrode dislocations (9.7%). The study limitations included the retrospective nature, lack of controls receiving placebo intervention, and randomization.

Conclusions: After careful patient selection according to a positive response to a trial of ONS and/or SONS, clinically meaningful long-term benefit was achieved in 57.1% of our patients with various chronic headache conditions.
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http://dx.doi.org/10.1016/j.wneu.2021.04.070DOI Listing
April 2021

Epilepsy surgery in stroke-related epilepsy.

Seizure 2021 May 5;88:116-124. Epub 2021 Apr 5.

Epilepsy Program, Department of Clinical Neurological Sciences, Schulich School of Medicine and Dentistry, Western University, 339 Windermere Rd. London, Ontario, Canada, N6A 5A5; Department of Epidemiology and Biostatistics, Schulich School of Medicine and Dentistry, Western University, 339 Windermere Rd. London, Ontario, Canada, N6A 5A5; Neuro-Epidemiology Unit, Schulich School of Medicine and Dentistry, Western University, 339 Windermere Rd. London, Ontario, Canada, N6A 5A5. Electronic address:

Purpose: To provide a descriptive analysis on the presurgical evaluation and surgical management of a cohort of patients with stroke related epilepsy (SRE).

Methods: We retrospectively examined the clinical characteristics, results of non-invasive and invasive presurgical evaluation, surgical management and outcome of consecutive patients with drug-resistant SRE in our institution from January 1, 2013 to January 1, 2020.

Results: Twenty-one of 420 patients (5%) who underwent intracranial EEG (iEEG), resective epilepsy surgery and/or vagus nerve stimulation (VNS) placement, had SRE. Of 13 patients who had iEEG, the ictal onset (IO) was exclusively within the stroke lesion in only one patient. In five patients the IO was extra-lesional and in the remaining seven patients it included the stroke lesion as well as extra-lesional structures. The IO included the mesial temporal region in 11 of the 13 patients (85%). The posterior margin of the stroke lesion was always involved. Five patients underwent surgery without iEEG. In total, 10 patients underwent resective surgery, four VNS placement and two had both corpus callosotomy and VNS placement. Of the patients who had resective surgery, nine were Engel I or II at last follow up.

Conclusion: We found that seizures in patients with drug resistant SRE were more frequently originated in the mesial temporal region than in the stroke lesion itself. Despite the complex epileptic network underlying drug-resistant SRE, a thorough presurgical assessment and adequate use of surgical options can lead to excellent surgical outcomes.
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http://dx.doi.org/10.1016/j.seizure.2021.04.002DOI Listing
May 2021

All that glitters: Contribution of stereo-EEG in patients with lesional epilepsy.

Epilepsy Res 2021 Feb 2;170:106546. Epub 2021 Jan 2.

Department of Clinical Neurological Sciences, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada; Department of Epidemiology and Biostatistics, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada; Neuro-Epidemiology Unit, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada. Electronic address:

Objective: To determine the contribution of stereo-EEG for localization purpose in patients with a visible lesion on MRI.

Background: Intracranial EEG is often used to localize the epileptogenic focus in patients with non-lesional focal epilepsy. Its role in cases where a lesion is visible on MRI can be even more complex and the relationship between the lesion and the seizure onset has rarely been addressed.

Methods: All consecutive patients between February 2013 and May 2018 who underwent stereo-EEG and had a lesion visible on MRI were included. We assessed the localization of the seizure onset and its relationship with the lesion. Clinical, radiological, and electrographic analyses were performed.

Results: Stereo-EEG revealed a seizure onset with either partial or no overlap with the lesion seen on MRI in 42 (56 %) of the 75 lesions included. Mesial temporal sclerosis was the only lesion type associated with an exclusively lesional seizure onset (p = 0.003).

Conclusion: Epilepsy surgery in MRI-positive cases should rely not only the results of lesions seen on MRI, which might be potentially misleading; SEEG is a gold standard method in these cases to define resective borders.
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http://dx.doi.org/10.1016/j.eplepsyres.2020.106546DOI Listing
February 2021

Paresthesia-Free Spinal Nerve Root Stimulation for the Treatment of Chronic Neuropathic Pain.

Neuromodulation 2020 Aug 28;23(6):831-837. Epub 2020 Jul 28.

Department of Clinical Neurological Sciences, London Health Sciences Centre, Western University, London, ON, Canada.

Objective: Stimulation of the dorsal spinal roots, or spinal nerve root stimulation (SNRS), is a neuromodulation modality that can target pain within specific dermatomal distributions. The use of paresthesia-free stimulation has been described with conventional dorsal column spinal cord stimulation, although has yet to be described for SNRS. This objective of this study was to investigate the efficacy of paresthesia-free high-frequency (1000-1200 Hz) SNRS in the treatment of intractable, dermatomal neuropathic pain.

Materials And Methods: A retrospective chart review was performed on 14 patients implanted with SNRS in varying distributions: Ten patients initially received tonic stimulation and crossed over to a paresthesia-free paradigm and four patients received only paresthesia-free stimulation. The primary outcome was reduction in pain severity (visual analog scale [VAS]), measured at baseline and follow-up to 24 months with paresthesia-free stimulation.

Results: All 14 patients who received paresthesia-free stimulation had significant improvement in pain severity at a mean follow-up of 1.39 ± 0.15 years (VAS 7.46 at baseline vs. 3.25 at most recent follow-up, p < 0.001). Ten patients were initially treated with tonic stimulation and crossed over to paresthesia-free stimulation after a mean of 61.7 months. Baseline pain in these crossover patients was significantly improved at last follow-up with tonic stimulation (VAS 7.65 at baseline vs. 2.83 at 48 months, p < 0.001), although all patients developed uncomfortable paresthesias. There was no significant difference in pain severity between patients receiving tonic and paresthesia-free stimulation.

Conclusions: We present real-world outcomes of patients with intractable dermatomal neuropathic pain treated with paresthesia-free, high-frequency SNRS. We demonstrate its effectiveness in providing pain reduction at a level comparable to tonic SNRS up to 24 months follow-up, without producing uncomfortable paresthesias.
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http://dx.doi.org/10.1111/ner.13236DOI Listing
August 2020

Direct visualization and characterization of the human zona incerta and surrounding structures.

Hum Brain Mapp 2020 11 17;41(16):4500-4517. Epub 2020 Jul 17.

Department of Clinical Neurological Sciences, Division of Neurosurgery, Western University, London, Ontario, Canada.

The zona incerta (ZI) is a small gray matter region of the deep brain first identified in the 19th century, yet direct in vivo visualization and characterization has remained elusive. Noninvasive detection of the ZI and surrounding region could be critical to further our understanding of this widely connected but poorly understood deep brain region and could contribute to the development and optimization of neuromodulatory therapies. We demonstrate that high resolution (submillimetric) longitudinal (T1) relaxometry measurements at high magnetic field strength (7 T) can be used to delineate the ZI from surrounding white matter structures, specifically the fasciculus cerebellothalamicus, fields of Forel (fasciculus lenticularis, fasciculus thalamicus, and field H), and medial lemniscus. Using this approach, we successfully derived in vivo estimates of the size, shape, location, and tissue characteristics of substructures in the ZI region, confirming observations only previously possible through histological evaluation that this region is not just a space between structures but contains distinct morphological entities that should be considered separately. Our findings pave the way for increasingly detailed in vivo study and provide a structural foundation for precise functional and neuromodulatory investigation.
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http://dx.doi.org/10.1002/hbm.25137DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7555067PMC
November 2020

Stereoelectroencephalography Versus Subdural Strip Electrode Implantations: Feasibility, Complications, and Outcomes in 500 Intracranial Monitoring Cases for Drug-Resistant Epilepsy.

Neurosurgery 2020 07;87(1):E23-E30

Department of Clinical Neurological Sciences, Schulich School of Medicine and Dentistry, Western University, London, Canada.

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.
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http://dx.doi.org/10.1093/neuros/nyaa112DOI Listing
July 2020

Seizure Freedom in Temporal Plus Epilepsy Surgery Following Stereo-Electroencephalography.

Can J Neurol Sci 2020 05;47(3):374-381

Department of Clinical Neurological Sciences, Western University, London, Ontario, Canada.

Background: "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.

Objective: We present a small case series of temporal plus cases successfully identified by SEEG who were seizure-free after resective surgery.

Methods: 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.

Results: 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.

Conclusion: 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.
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http://dx.doi.org/10.1017/cjn.2020.26DOI Listing
May 2020

Effect of Training on Percutaneous Glycerol Rhizotomy for Trigeminal Neuralgia: A Long-Term, Retrospective Comparison of Staff Neurosurgeon and Trainee Complications and Efficacy.

World Neurosurg 2020 Feb 19;134:e1001-e1007. Epub 2019 Nov 19.

Division of Neurosurgery, Department of Clinical Neurological Sciences, London Health Sciences Centre, Western University, London, Ontario, Canada.

Objective: The role of trainee involvement in lesioning procedures for trigeminal neuralgia (TN) has not yet been investigated in reported studies. The objective of the present study was to compare the complications and efficacy of percutaneous glycerol rhizotomy (GR) when performed by staff neurosurgeons and trainees.

Methods: A retrospective medical record analysis of 165 patients with medically refractory TN who had undergone 293 GR procedures by either a staff attending (n = 156) or trainee (n = 137) from 2007 to 2018 was performed. The data were analyzed with respect to procedure time, fluoroscopy time and radiation exposure, complication rates and outcomes.

Results: No difference was found in procedure duration between the teaching and nonteaching cases and only a nonsignificant trend was found toward a longer fluoroscopy time for the latter. The initial response rates to GR were equal for staff attending (88.7%) and trainee (87.2%) cases (P = 0.708). Similarly, no statistically significant difference (P = 0.48) was found between the median time to recurrence for the staff attending cases (1.6 ± 0.3 years) compared with that of the trainee cases (1.7 ± 0.3 years). The overall incidence of complications was low (7.5%). The occurrence of facial hypoesthesia correlated with the amount of glycerol injected (P < 0.01).

Conclusions: GR for the treatment of TN can safely be performed by senior residents and fellows under supervision.
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http://dx.doi.org/10.1016/j.wneu.2019.11.058DOI Listing
February 2020

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

Oper Neurosurg (Hagerstown) 2020 03;18(3):278-283

Department of Clinical Neurological Sciences, Schulich School of Medicine and Dentistry, Western University, London, Canada.

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.
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http://dx.doi.org/10.1093/ons/opz154DOI Listing
March 2020

Percutaneous glycerol rhizotomy for trigeminal neuralgia in patients with multiple sclerosis: a long-term retrospective cohort study.

J Neurosurg 2019 Apr 12;132(5):1405-1413. Epub 2019 Apr 12.

1Department of Clinical Neurological Sciences, Division of Neurosurgery, London Health Sciences Centre, Western University, London, Ontario, Canada; and.

Objective: The prevalence of trigeminal neuralgia (TN) in patients with multiple sclerosis (MS-TN) is higher than in the general population (idiopathic TN [ITN]). Glycerol rhizotomy (GR) is a percutaneous lesioning surgery commonly performed for the treatment of medically refractory TN. While treatment for acute pain relief is excellent, long-term pain relief is poorer. The object of this study was to assess the efficacy of percutaneous retrogasserian GR for the treatment of MS-TN versus ITN.

Methods: A retrospective chart review was performed, identifying 219 patients who had undergone 401 GR procedures from 1983 to 2018 at a single academic institution. All patients were diagnosed with medically refractory MS-TN (182 procedures) or ITN (219 procedures). The primary outcome measures of interest were immediate pain relief and time to pain recurrence following initial and repeat GR procedures. Secondary outcomes included medication usage and presence of periprocedural hypesthesia.

Results: The initial pain-free response rate was similar between groups (p = 0.726): MS-TN initial GR 89.6%; MS-TN repeat GR 91.9%; ITN initial GR 89.6%; ITN repeat GR 87.0%. The median time to recurrence after initial GR was similar between MS-TN (2.7 ± 1.3 years) and ITN (2.1 ± 0.6 years) patients (p = 0.87). However, there was a statistically significant difference in the time to recurrence after repeat GR between MS-TN (2.3 ± 0.5 years) and ITN patients (1.2 ± 0.2 years; p < 0.05). The presence of periprocedural hypesthesia was highly predictive of pain-free survival (p < 0.01).

Conclusions: Patients with MS-TN achieve meaningful pain relief following GR, with an efficacy comparable to that following GR in patients with ITN. Initial and subsequent GR procedures are equally efficacious.
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http://dx.doi.org/10.3171/2019.1.JNS183093DOI Listing
April 2019

An assessment of K channel function in human cerebral arteries.

Am J Physiol Heart Circ Physiol 2019 04 25;316(4):H794-H800. Epub 2019 Jan 25.

Department of Physiology and Pharmacology, University of Western Ontario , London, Ontario , Canada.

In the rodent cerebral circulation, inward rectifying K (K) channels set resting tone and the distance over which electrical phenomena spread along the arterial wall. The present study sought to translate these observations into human cerebral arteries obtained from resected brain tissue. Computational modeling and a conduction assay first defined the impact of K channels on electrical communication; patch-clamp electrophysiology, quantitative PCR, and immunohistochemistry then characterized K2.x channel expression/activity. In keeping with rodent observations, computer modeling highlighted that K blockade should constrict cerebral arteries and attenuate electrical communication if functionally expressed. Surprisingly, Ba (a K channel inhibitor) had no effect on human cerebral arterial tone or intercellular conduction. In alignment with these observations, immunohistochemistry and patch-clamp electrophysiology revealed minimal K channel expression/activity in both smooth muscle and endothelial cells. This absence may be reflective of chronic stress as dysphormic neurons, leukocyte infiltrate, and glial fibrillary acidic protein expression was notable in the epileptic cortex. In closing, K2.x channel expression is limited in human cerebral arteries from patients with epilepsy and thus has little impact on resting tone or the spread of vasomotor responses. NEW & NOTEWORTHY K2.x channels are expressed in rodent cerebral arterial smooth muscle and endothelial cells. As they are critical to setting membrane potential and the distance signals conduct, we sought to translate this work into humans. Surprisingly, K2.x channel activity/expression was limited in human cerebral arteries, a paucity tied to chronic brain stress in the epileptic cortex. Without substantive expression, K2.x channels were unable to govern arterial tone or conduction.
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http://dx.doi.org/10.1152/ajpheart.00022.2019DOI Listing
April 2019

Spontaneous Regression of an Intraparenchymal Cyst Following Deep Brain Stimulator Electrode Implantation: Case Report and Literature Review.

World Neurosurg 2018 Sep 22;117:249-254. Epub 2018 Jun 22.

Department of Clinical Neurological Sciences, London Health Sciences Centre, Western University, London, Ontario, Canada.

Background: The development of an intraparenchymal cyst following deep brain stimulation (DBS) surgery is an uncommon complication that lacks a clearly defined management strategy. The pathophysiology is not known and may be related to perielectrode edema or cerebrospinal fluid tracking. Previous case reports have described various therapies for symptomatic cysts, including hardware removal or conservative treatment with steroids.

Case Description: We present a male patient with bilateral DBS of the ventral intermediate nucleus of the thalamus for management of essential tremor, who developed a cystic cavitation at the left electrode tip and was followed without treatment. This patient developed dysarthria, gait impairment, and unilateral motor deficits 3 months after surgery. Perielectrode edema was initially identified, eventually coalescing into a cystic cavitation at the electrode tip. Cystic regression and symptomatic improvement were observed without any surgical or medical intervention, with full cyst resolution by 17 months.

Conclusions: Only 15 additional cases have been reported in the literature, although the true incidence may be underreported because of varying practices in obtaining postoperative scans. Cysts were identified in symptomatic patients on average 6.2 months after surgery. All symptomatic cysts were treated with hardware removal or steroid therapy. Observation alone may be sufficient when a DBS-associated cyst is identified. More reports are needed to characterize this rare complication.
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http://dx.doi.org/10.1016/j.wneu.2018.06.115DOI Listing
September 2018

Intracranial Electroencephalographic Monitoring: From Subdural to Depth Electrodes.

Can J Neurol Sci 2018 05 12;45(3):336-338. Epub 2018 Apr 12.

Epilepsy Program,Department of Clinical Neurological Sciences,Schulich School of Medicine and Dentistry,Western University,London,Ontario,Canada.

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.
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http://dx.doi.org/10.1017/cjn.2018.4DOI Listing
May 2018

Prohibited Arc Angles During Leksell Frame-Based Stereotaxy.

World Neurosurg 2018 Apr 31;112:123-125. Epub 2018 Jan 31.

Epilepsy Program, Department of Clinical Neurological Sciences, Division of Neurosurgery, London Health Sciences Centre, University Hospital, London, Ontario, Canada. Electronic address:

Background: During Leksell frame-based stereotaxy the lateral trajectory can be obstructed by the arc supports at certain combinations of the X-coordinate and arc angle.

Objective: To provide a matrix with usable and prohibited combinations of the X-coordinate and arc angle to faciliate finding lateral stereotactic trajectories with the Leksell frame in standard configuration.

Methods: Various combination settings of the X-coordinate and arc angle were tested for a Leksell Multi-Purpose Stereotactic Arc mounted on a Leksell Coordinate Frame G.

Results: A matrix of usable and prohibited combinations of the X-coordinate and arc angle is provided.

Conclusions: The matrix will help to facilitate surgical work flow during stereotactic procedures involving the Leksell frame.
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http://dx.doi.org/10.1016/j.wneu.2018.01.068DOI Listing
April 2018

Operative Nuances of Stereotactic Leksell Frame-Based Depth Electrode Implantation.

Oper Neurosurg (Hagerstown) 2018 09;15(3):292-295

Epilepsy Program, Department of Clinical Neurological Sciences, Division of Neu-rosurgery, London Health Sciences Cen-tre, University Hospital, London, Ontario, Canada.

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.
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http://dx.doi.org/10.1093/ons/opx245DOI Listing
September 2018

Ultra-High Field Template-Assisted Target Selection for Deep Brain Stimulation Surgery.

World Neurosurg 2017 Jul 17;103:531-537. Epub 2017 Apr 17.

Imaging Research Laboratories, Robarts Research Institute, Western University, London, Ontario, Canada; Biomedical Engineering Graduate Program, Western University, London, Ontario, Canada; Department of Medical Biophysics, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.

Background: Template and atlas guidance are fundamental aspects of stereotactic neurosurgery. The recent availability of ultra-high field (7 Tesla) magnetic resonance imaging has enabled in vivo visualization at the submillimeter scale. In this Doing More with Less article, we describe our experiences with integrating ultra-high field template data into the clinical workflow to assist with target selection in deep brain stimulation (DBS) surgical planning.

Methods: The creation of a high-resolution 7T template is described, generated from group data acquired at our center. A computational workflow was developed for spatially aligning the 7T template with standard clinical data and furthermore, integrating the derived imaging volumes into the surgical planning workstation.

Results: We demonstrate that our methodology can be effective for assisting with target selection in 2 cases: unilateral internal pallidum DBS for painful dystonia and bilateral subthalamic nucleus DBS for Parkinson's disease.

Conclusions: In this article, we have described a workflow for the integration of high-resolution in vivo ultra-high field templates into the surgical navigation system as a means to assist with DBS planning. The method does not require any additional cost or time to the patient. Future work will include prospectively evaluating different templates and their impact on target selection.
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http://dx.doi.org/10.1016/j.wneu.2017.04.043DOI Listing
July 2017

Successful Long-term Nerve Root Stimulation for Chronic Neuropathic Pain: A Real World, Single Center Canadian Experience.

Pain Physician 2017 02;20(2):95-106

Department of Clinical Neurological Sciences, Division of Neurosurgery Western University; London, ON, Canada.

Background: 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.

Objectives: In this study we report our experience treating patients with chronic neuropathic pain using SCS and DNRS.

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.

Methods: 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).

Results: 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.

Limitations: 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.

Conclusions: 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.
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February 2017

Quantification of local geometric distortion in structural magnetic resonance images: Application to ultra-high fields.

Neuroimage 2018 03 6;168:141-151. Epub 2017 Jan 6.

Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada; Biomedical Engineering Graduate Program, Western University, London, Ontario, Canada; Department of Medical Biophysics, Western University, London, Ontario, Canada.

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.
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http://dx.doi.org/10.1016/j.neuroimage.2016.12.066DOI Listing
March 2018

Cervical Spinal Cord and Dorsal Nerve Root Stimulation for Neuropathic Upper Limb Pain.

Can J Neurol Sci 2017 Jan 23;44(1):83-89. Epub 2016 Sep 23.

Department of Clinical Neurological Sciences,Division of Neurosurgery,Western University,London,ON,Canada.

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.
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http://dx.doi.org/10.1017/cjn.2016.294DOI Listing
January 2017

Stimulation of the Spinal Cord and Dorsal Nerve Roots for Chronic Groin, Pelvic, and Abdominal Pain.

Pain Physician 2016 07;19(6):405-12

Department of Clinical Neurological Sciences, Division of Neurosurgery Western University; London, ON, Canada.

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.
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July 2016

New-Onset Stutter After Electrode Insertion in the Ventrocaudalis Nucleus for Face Pain.

World Neurosurg 2016 Jun 28;90:703.e7-703.e10. Epub 2016 Feb 28.

Division of Neurosurgery, Department of Clinical Neurological Sciences, Western University, London, Ontario, Canada.

Background: Deep brain stimulation (DBS) of the ventrocaudalis nucleus of the thalamus is a last resort treatment for chronic refractory pain. DBS is generally a safe procedure, although it can result in functional disturbances depending on the site of stimulation. There has been 1 previous report of stuttering induced by microlesioning of the thalamus, as well as several reports of stuttering induced by stimulation of the thalamus and other related structures in the brain.

Case Description: We describe the case of a patient with trigeminal deafferentation face pain who was treated with DBS of the ventrocaudalis nucleus thalamus and developed a reversible stutter immediately on insertion of the electrode. The stutter improved significantly over 12 days after implant; however, the device was not effective in relieving the patient's pain and was removed.

Conclusions: Stuttering is a rare complication of deep brain exploration of the sensory thalamus. Our coordinates are near to but in a distinct anatomic region compared with cases previously described as having similar effects on speech.
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http://dx.doi.org/10.1016/j.wneu.2016.02.085DOI Listing
June 2016

Supplementary implantation of intracranial electrodes in the evaluation for epilepsy surgery.

Epilepsy Res 2009 Nov 19;87(1):95-101. Epub 2009 Aug 19.

Epilepsy Programme, Department of Clinical Neurological Sciences, University of Western Ontario, London, ON, Canada N6A 5A5.

Purpose: In some patients, resective epilepsy surgery can be planned based on a non-invasive work-up. However, in many cases, invasive monitoring with intracranial electrodes is required prior to recommending a resective procedure. Although the results of intracranial recordings are usually conclusive, a small group of patients may require additional electrodes to better define the seizure onset or propagation.

Methods: One hundred and seventy seven patients who underwent intracranial electrode insertion between January 2000 and June 2005 were reviewed. Twelve of these patients required a supplementary implantation prior to making a recommendation about resective surgery. We report the nature of implantation as well as the outcomes in these 12 patients.

Results: The mean age of these patients was 35 years (7 males). An average of 2.5 additional strip electrodes were required resulting in a mean of 9 strip type electrodes per patient, for a mean total of an additional 20 days. For most patients (9/12) this subsequent procedure identified an area of epileptic cortex other than that originally hypothesized. Seven patients went on to surgery of which three experienced a significant improvement in seizure control.

Conclusions: The addition of supplementary electrodes to an ongoing invasive electrode investigation can be a useful means of clarifying a patient's suitability for a resective surgical procedure. While the surgical outcomes may not be as favorable as in patients in whom the investigations are simpler, a proportion of these patients do benefit from the eventual resective procedure. In cases where the supplementary electrodes lead to the conclusion that surgery is not indicated, these patients can be satisfied that the surgical option has been explored to the fullest extent possible.
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http://dx.doi.org/10.1016/j.eplepsyres.2009.07.003DOI Listing
November 2009

Outcome of epilepsy surgery in patients investigated with subdural electrodes.

Epilepsy Res 2009 Aug 19;85(2-3):235-42. Epub 2009 Apr 19.

Epilepsy Programme, Department of Clinical Neurological Sciences, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada.

Invasive intracranial electrodes (IE) are an important part of the work-up in many patients being considered for epilepsy surgery. Because IE are usually reserved for cases where seizure localization is ambiguous, one might expect that the eventual outcome of epilepsy surgery in these patients would be worse than in patients who did not require IE as part of their work-up. The purpose of this study was to specifically examine those patients who underwent insertion of subdural electrodes, to determine how many of these patients eventually underwent resective surgery of any type and to assess the eventual outcome. All cases admitted for subdural electrodes between January 2000 and June 2005 were reviewed. Surgical outcomes were reported using the Engel classification and a multivariate analysis was used to determine which factors were associated with successful surgery. 177 IE implantations were performed in 172 patients. Of these, 130 patients went on to have surgery. In the 113 of the 130 surgical patients in whom 1-year follow-up was available, 47% were seizure free at 1 year. Age was a major predictor of outcome with only 21% of patients over age 40 becoming seizure free with surgery compared to 58% in patients aged under 40 years (p=0.0004). Other predictors of an Engel I outcome included having a temporal lobectomy or supplementary motor area resection. Good results from eventual resective surgery can be achieved in patients needing invasive recordings. Younger patients with temporal lobe epilepsy seem to have the highest likelihood of seizure freedom.
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http://dx.doi.org/10.1016/j.eplepsyres.2009.03.014DOI Listing
August 2009