Publications by authors named "Samuel Strantzas"

21 Publications

  • Page 1 of 1

Supplementing Extraoperative Electrocorticography With Real-Time Intraoperative Recordings Using the Same Chronically Implanted Electrodes.

Oper Neurosurg (Hagerstown) 2021 Feb 8. Epub 2021 Feb 8.

Division of Neurosurgery, Department of Surgery, University of Toronto, Toronto, Ontario, Canada.

Background: The practice of intraoperative electrocorticography (iECoG) to guide resective epilepsy surgery is variable. Limitations of iECoG include variability in recordings from previously unsampled cortex, increased operative time and cost, and a lack of clear benefit to surgical decision-making.

Objective: To describe a simple technique to supplement extraoperative intracranial recordings with real-time iECoG using the same chronically implanted electrodes that overcome some of these limitations.

Methods: We describe the technical procedure, intraoperative findings, and outcomes of 7 consecutive children undergoing 2-stage resective epilepsy surgery with invasive subdural grid monitoring between January 2017 and December 2019. All children underwent placement of subdural grids, strips, and depth electrodes. Planned neocortical resection was based on extraoperative mapping of ictal and interictal recordings. During resection in the second stage, the same electrodes were used to perform real-time iECoG.

Results: Real-time iECoG using this technique leads to modification of resection for 2 of the 7 children. The first was extended due to an electroencephalographic seizure from a distant electrode not part of the original resection plan. The second was restricted due to attenuation of epileptiform activity following a partial resection, thereby limiting the extent of a Rolandic resection. No infections or other adverse events were encountered.

Conclusion: We report a simple technique to leverage chronically implanted electrodes for real-time iECoG during 2-stage resective surgery. This technique presents fewer limitations than traditional approaches and may alter intraoperative decision-making.
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February 2021

What is the Optimal Surgical Method for Achieving Correction and Avoiding Neurological Complications in Pediatric High-grade Spondylolisthesis?

J Pediatr Orthop 2021 Mar;41(3):e217-e225

Department of Orthopaedic Surgery, Hospital for Sick Children, Toronto, ON, Canada.

Background: Controversy persists in the treatment of high-grade spondylolisthesis (HGS). Surgery is recommended in patients with intrusive symptoms and evidence debates the competing strategies. This study compares the radiologic outcomes and postoperative complications at a minimum of 2 years follow-up for patients with HGS treated with instrumented fusion with partial reduction (IFIS) with those treated with reduction, decompression, and instrumented fusion (RIF). We hypothesize that IFIS leads to a lower rate of complication and revision surgery than RIF.

Methods: A retrospective comparative methodology was used to analyze consecutive HGS treated surgically between 2006 and 2017. Patients diagnosed with ≥grade 3 spondylolisthesis treated with arthrodesis before the age of 18 years with a minimum of 2 years follow-up were included. Patients were excluded if surgery did not aim to achieve arthrodesis or was a revision procedure. Cases were identified through departmental and neurophysiological records.

Results: Thirty patients met the inclusion criteria. Mean follow-up was 4 years. Ten patients underwent IFIS and the remaining 20 underwent RIF. The 2 groups showed no difference in demographics, grade of slip, deformity or presenting symptoms. Of 10 treated with IFIS, the SA reduced by a mean of 10 degrees and C7 sagittal vertical line changed by 31 mm. In the RIF cohort, SA reduced by 16 degrees and C7 sagittal vertical line reduced by 26 mm. PT was unchanged in both groups. In IFIS cohort, 2 patients showed postoperative weakness, resolved by 2 years. None required revision surgery. In the RIF group, 4 sustained dural tears and 1 a laminar fracture, 7 showed postoperative weakness or dysaesthesia, 3 of which had not resolved by 2 years. Eight patients underwent unplanned further surgery, 3 for pseudarthrosis.

Conclusions: RIF and IFIS show similar radiologic outcomes. RIF shows a higher rate of unplanned return to surgery, pseudarthrosis and persisting neurological changes.

Level Of Evidence: Level III-retrospective comparative study.
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March 2021

Feasibility of awake craniotomy in the pediatric population.

Paediatr Anaesth 2020 07;30(7):842-843

Department of Neurophysiology, The Hospital for Sick Children, Toronto, ON, Canada.

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July 2020

The effect of dexmedetomidine on motor-evoked potentials during pediatric posterior spinal fusion surgery: a retrospective case-control study.

Can J Anaesth 2020 Oct 22;67(10):1341-1348. Epub 2020 Jul 22.

Department of Anesthesia and Pain Medicine, The Hospital for Sick Children, University of Toronto, 555 University Avenue, Toronto, ON, M5G 1X8, Canada.

Purpose: Motor-evoked potentials (MEPs) are frequently used in pediatric posterior spinal fusion surgery (PSFS) to detect spinal cord ischemia. Dexmedetomidine is increasingly being used as an adjunct to total intravenous anesthesia, but its effect on MEP amplitude has been variably reported. The purpose of this study was to evaluate the effect of an infusion of dexmedetomidine on the amplitude of MEPs.

Methods: We performed a retrospective case-control study of 30 pediatric patients who received a 0.5 µg·kg·hr infusion of dexmedetomidine, ten patients who received 0.3 µg·kg·hr dexmedetomidine, and 30 control patients who did not receive dexmedetomidine during PSFS. Two neurophysiologists reviewed the MEP amplitudes in six muscle groups at three time points: when the patient was turned prone (baseline; T1), one hour after incision (T2), and after exposure of the spine but before insertion of the first screw (T3).

Results: In all muscles tested, the mean MEP amplitude was reduced by T3 when dexmedetomidine was infused at 0.5 µg·kg·hr. The greatest reduction from baseline MEP amplitude was 829 µV (95% confidence interval, 352 to 1230; P < 0.001) seen in first right dorsus interosseous. When dexmedetomidine was infused at 0.3 µg·kg·hr, there was a significant reduction in MEP amplitude in four of the six muscles tested at T3 compared with the control group.

Conclusions: Dexmedetomidine at commonly used infusion rates of 0.3 µg·kg·hr or 0.5 µg·kg·hr causes a significant decrease in MEP amplitude during pediatric PSFS. We suggest that dexmedetomidine should be avoided in children undergoing PSFS so as not to confuse the interpretation of this important neurophysiological monitor.
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October 2020

Selective dorsal rhizotomy: an illustrated review of operative techniques.

J Neurosurg Pediatr 2020 Feb 7:1-8. Epub 2020 Feb 7.

1Division of Neurosurgery, Department of Surgery, University of Toronto.

Objective: Selective dorsal rhizotomy (SDR) is a procedure primarily performed to improve function in a subset of children with limitations related to spasticity. There is substantial variability in operative techniques among centers and surgeons. Here, the authors provide a technical review of operative approaches for SDR.

Methods: Ovid MEDLINE, Embase, and PubMed databases were queried in accordance with PRISMA guidelines. All studies included described a novel surgical technique. The technical nuances of each approach were extracted, including extent of exposure, bone removal, and selection of appropriate nerve roots. The operative approach preferred at the authors' institution (the "2 × 3 exposure") is also detailed.

Results: Five full-text papers were identified from a total of 380 articles. Operative approaches to SDR varied significantly with regard to level of exposure, extent of laminectomy, and identification of nerve roots. The largest exposure involved a multilevel laminectomy, while the smallest exposure involved a keyhole interlaminar approach. At the Hospital for Sick Children, the authors utilize a two-level laminoplasty at the level of the conus medullaris. The benefits and disadvantages of the spectrum of techniques are discussed, and illustrative figures are provided.

Conclusions: Surgical approaches to SDR vary considerably and are detailed and illustrated in this review as a guide for neurosurgeons. Future studies should address the long-term impact of these techniques on functional outcomes and complications such as spinal deformity.
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February 2020

Feasibility of awake craniotomy in the pediatric population.

Paediatr Anaesth 2020 04 13;30(4):480-489. Epub 2020 Feb 13.

Department of Anesthesia, The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada.

Background: Awake craniotomy with direct cortical stimulation and mapping is the gold standard for resection of lesions near eloquent brain areas, as it can maximize the extent of resection while minimizing the risk of neurological damage. In contrast to the adult population, only small series of awake craniotomies have been reported in children.

Aims: The aim of our study is to establish the feasibility of awake craniotomy in the pediatric population.

Methods: We performed a retrospective observational study of children undergoing a supratentorial awake craniotomy between January 2009 and April 2019 in a pediatric tertiary care center. Our primary outcome was feasibility of awake craniotomy, defined as the ability to complete the procedure without conversion to general anesthesia. Our secondary outcomes were the incidence of serious intraoperative complications and the mapping completion rate.

Results: Thirty procedures were performed in 28 children: 12 females and 16 males. The median age was 14 years (range 7-17). The primary diagnosis was tumor (83.3%), epilepsy (13.3%), and arterio-venous malformation (3.3%). The anesthetic techniques were asleep-awake-asleep (96.7%) and conscious sedation (3.3%), all cases supplemented with scalp block and pin-site infiltration. Awake craniotomy was feasible in 29 cases (96.7%), one patient converted to general anesthesia due to agitation. Serious complications occurred in six patients: agitation (6.7%), seizures (3.3%), increased intracranial pressure (3.3%), respiratory depression (3.3%), and bradycardia (3.3%). All complications were quickly resolved and without major consequences. Cortical mapping was completed in 96.6% cases. New neurological deficits occurred in six patients (20%)-moderate in one case and mild in 5-being all absent at 6 months of follow-up.

Conclusion: Awake craniotomy with intraoperative mapping can be successfully performed in children. Adequate patient selection and close cooperation between neurosurgeons, anesthesiologists, neuropsychologists, and neurophysiologists is paramount. Further studies are needed to determine the best anesthetic technique in this population group.
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April 2020

Responding to Intraoperative Neuromonitoring Changes During Pediatric Coronal Spinal Deformity Surgery.

Global Spine J 2019 May 8;9(1 Suppl):15S-21S. Epub 2019 May 8.

AOSpine Knowledge Forum Deformity, Davos, Switzerland.

Study Design: Retrospective case study on prospectively collected data.

Objectives: The purpose of this explorative study was: 1) to determine if patterns of spinal cord injury could be detected through intra-operative neuromonitoring (IONM) changes in pediatric patients undergoing spinal deformity corrections, 2) to identify if perfusion based or direct trauma causes of IONM changes could be distinguished, 3) to observe the effects of the interventions performed in response to these events, and 4) to attempt to identify different treatment algorithms for the different causes of IONM alerts.

Methods: Prospectively collected neuromonitoring data in pre-established forms on consecutive pediatric patients undergoing coronal spinal deformity surgery at a single center was reviewed. Real-time data was collected on IONM alerts with >50% loss in signal. Patients with alerts were divided into 2 groups: unilateral changes (direct cord trauma), and bilateral MEP changes (cord perfusion deficits).

Results: A total of 97 pediatric patients involving 71 females and 26 males with a mean age of 14.9 (11-18) years were included in this study. There were 39 alerts in 27 patients (27.8% overall incidence). All bilateral changes responded to a combination of transfusion, increasing blood pressure, and rod removal. Unilateral changes as a result of direct trauma, mainly during laminotomies for osteotomies, improved with removal of the causative agent. Following corrective actions in response to the alerts, all cases were completed as planned. Signal returned to near baseline in 20/27 patients at closure, with no new neurological deficits in this series.

Conclusion: A high incidence of alerts occurred in this series of cases. Dividing IONM changes into perfusion-based vs direct trauma directed treatment to the offending cause, allowing for safe corrections of the deformities. Patients did not need to recover IONM signal to baseline to have a normal neurological examination.
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May 2019

Intra-operative cortical motor mapping using subdural grid electrodes in children undergoing epilepsy surgery evaluation and comparison with the conventional extra-operative motor mapping.

Clin Neurophysiol 2018 12 12;129(12):2642-2649. Epub 2018 Aug 12.

Epilepsy Program, Division of Neurology, Department of Pediatrics, The Hospital for Sick Children, Toronto, Ontario, Canada. Electronic address:

Objectives: The objective of this study was to review our experience with intra-operative "train of five" stimulation using subdural grid for motor mapping in children undergoing epilepsy surgery evaluation.

Methods: Twenty consecutive children below 18-years of age with drug-refractory epilepsy who underwent invasive-EEG monitoring using subdural-grid placement and intra-operative motor mapping using direct cortical stimulation by sub-dural grid electrodes (IODCS-SDG) at our institution between January-2016 and June-2017 were reviewed. Stimulation was delivered through the subdural-grid electrodes using a train-of-five pulses and muscle responses were recorded by motor-evoked-potentials (MEPs). Intra-operative direct cortical stimulation delivered through a ball-tipped probe (IODCS-probe) and extra-operative motor-mapping (EODCS-SDG) were also performed.

Results: IODCS-SDG was completed in 20 patients and subsequent EODCS-SDG was done in 17/20 patients. MEP responses were more commonly obtained in the deltoid (19/20), extensor-digitorum-communis (20/20) and first-dorsal-interosseus (19/20). The median thresholds varied between 40 V and 60 V for the six muscle groups. The respective IODCS-probe thresholds tended to be similar. No stimulation-provoked seizures or anaesthesia-related complications were noted during IODCS-SDG. EODCS-SDG could not be completed in 4/17 children and mapping data obtained was frequently inadequate. Nine patients demonstrated 100% concordance between IODCS-SDG and EODCS-SDG for the common mapped body regions. Stimulation-provoked seizures during EODCS-SDG were seen in 6/17 (35.3%) and after-discharges in 7/17 (41.2%) children.

Conclusions: IODCS-SDG could be performed safely in children with drug refractory epilepsy undergoing invasive EEG monitoring.

Significance: IODCS-SDG may be a useful adjunct to EODCS-SDG in motor mapping for children.
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December 2018

The Deformity Angular Ratio: Does It Correlate With High-Risk Cases for Potential Spinal Cord Monitoring Alerts in Pediatric 3-Column Thoracic Spinal Deformity Corrective Surgery?

Spine (Phila Pa 1976) 2015 Aug;40(15):E879-85

*Toronto Western Hospital, The Hospital for Sick Children, Toronto, Ontario, Canada; †Washington University in St. Louis, St. Louis, MO; ‡Toronto Western Hospital, Toronto, Ontario, Canada; and §Children's Hospital Los Angeles, Los Angeles, CA.

Study Design: A retrospective analysis.

Objective: The purpose of this study was to determine whether the deformity angular ratio (DAR) can reliably assess the neurological risks of patients undergoing deformity correction.

Summary Of Background Data: Identifying high-risk patients and procedures can help ensure that appropriate measures are taken to minimize neurological complications during spinal deformity corrections. Subjectively, surgeons look at radiographs and evaluate the riskiness of the procedure. However, 2 curves of similar magnitude and location can have significantly different risks of neurological deficit during surgery. Whether the curve spans many levels or just a few can significantly influence surgical strategies. Lenke et al have proposed the DAR, which is a measure of curve magnitude per level of deformity.

Methods: The data from 35 pediatric spinal deformity correction procedures with thoracic 3-column osteotomies were reviewed. Measurements from preoperative radiographs were used to calculate the DAR. Binary logistic regression was used to model the relationship between DARs (independent variables) and presence or absence of an intraoperative alert (dependent variable).

Results: In patients undergoing 3-column osteotomies, sagittal curve magnitude and total curve magnitude were associated with increased incidence of transcranial motor evoked potential changes. Total DAR greater than 45° per level and sagittal DAR greater than 22° per level were associated with a 75% incidence of a motor evoked potential alert, with the incidence increasing to 90% with sagittal DAR of 28° per level.

Conclusion: In patients undergoing 3-column osteotomies for severe spinal deformities, the DAR was predictive of patients developing intraoperative motor evoked potential alerts. Identifying accurate radiographical, patient, and procedural risk factors in the correction of severe deformities can help prepare the surgical team to improve safety and outcomes when carrying out complex spinal corrections.

Level Of Evidence: 3.
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August 2015

Transcutaneous electrical nerve stimulation as a novel method of remote preconditioning: in vitro validation in an animal model and first human observations.

Basic Res Cardiol 2014 May 7;109(3):406. Epub 2014 Mar 7.

The Division of Cardiology, Department of Paediatrics, Hospital for Sick Children, University of Toronto, 555 University Avenue, Toronto, ON, M5G1X8, Canada.

Remote ischemic preconditioning (rIPC) induced by transient limb ischemia (li-rIPC) leads to neurally dependent release of blood-borne factors that provide potent cardioprotection. We hypothesized that transcutaneous electrical nerve stimulation (TENS) is a clinically relevant stimulus of rIPC. Study 1: seven rabbits were subjected to lower limb TENS; six to li-rIPC, and six to sham intervention. Blood was drawn and used to prepare a dialysate for subsequent analysis of cardioprotection in rabbit Langendorff preparation. Study 2: 14 healthy adults underwent upper limb TENS stimulation on one study day, 10 of whom also underwent li-rIPC on another study day. Blood was drawn before and after each stimulus, dialysate prepared, and cardioprotective activity assessed in mouse Langendorff preparation. The infarct size and myocardial recovery were measured after 30 min of global ischemia and 60 or 120 min of reperfusion. Animal validation: compared to control, TENS induced marked cardioprotection with significantly reduced infarct size (TENS vs. sham p < 0.01, rIPC vs. sham p < 0.01, TENS vs. rIPC p = ns) and improved functional recovery during reperfusion. Human study: compared to baseline, dialysate after rIPC (pre-rIPC vs. post-rIPC, p < 0.001) and TENS provided potent cardioprotection (pre-TENS vs. post-TENS p < 0.001) and improved myocardial recovery during reperfusion. The cardioprotective effects of TENS dialysates were blocked by pretreatment of the receptor heart with the opioid antagonist naloxone. TENS is a novel method for inducing cardioprotection and may provide an alternative to the limb ischemia stimulus for induction of rIPC clinically.
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May 2014

Phasic genioglossus and palatoglossus muscle activity during recovery from sevoflurane anesthesia: a prospective observational study in children.

Anesthesiology 2013 Sep;119(3):562-8

Department of Anesthesia and Pain Medicine, University of Toronto, Toronto, Ontario, Canada.

Background: Inhalational anesthetic effects on upper airway muscle activity in children are largely unknown. The authors tested the hypothesis that phasic inspiratory genioglossus and palatoglossus activity increases during recovery from sevoflurane anesthesia in a dose-dependent manner in children.

Methods: Sixteen children, aged 2.0 to 6.9 yr, scheduled for elective urological surgery were studied. Electromyogram recordings were acquired using intramuscular needle electrodes during spontaneous ventilation. After a 15-min period of equilibration, electromyogram activity was recorded over 30 s at each of three end-tidal concentrations, 1.5, 1.0, and 0.5 minimum alveolar concentration (MAC), administered in sequence.

Results: Phasic genioglossus activity was noted in four children at 1.5 MAC, five at 1.0 MAC, and six children at 0.5 MAC sevoflurane. Phasic palatoglossus activity was noted in 4 children at 1.5 MAC, 6 at 1.0 MAC, and 10 children at 0.5 MAC sevoflurane. Both the proportion of children exhibiting phasic activity, and the magnitude of phasic activity increased during recovery from anesthesia. For the genioglossus, decreasing the depth of sevoflurane anesthesia from 1.5 to 1.0 MAC increased phasic activity by approximately 35% and a further decrease to 0.5 MAC more than doubled activity (median [range] at 1.5 and 0.5 MAC: 2.7 μV [0 to 4.0 μV] and 8.6 μV [3.2 to 17.6], respectively; P = 0.029). A similar dose-related increase was recorded at the palatoglossus (P = 0.0002).

Conclusions: Genioglossus and palatoglossus activity increases during recovery from sevoflurane anesthesia in a dose-dependent manner over the clinical range of sevoflurane concentrations in children.
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September 2013

Responding to neuromonitoring changes in 3-column posterior spinal osteotomies for rigid pediatric spinal deformities.

Spine (Phila Pa 1976) 2013 Apr;38(8):E493-503

Division of Orthopaedic Surgery, The Hospital for Sick Children, Toronto, Ontario, Canada.

Study Design: Retrospective review of prospectively collected data on the neuromonitoring changes recorded during a consecutive series of cord level 3-column posterior spinal osteotomies for the correction of rigid pediatric spinal deformities in children between 2005 and 2012.

Objective: To review the neuromonitoring changes observed during the performance of these procedures, to highlight the high-risk steps, and to describe actions taken to avert major neurological injury.

Summary Of Background Data: Significant motor evoked potentials (MEP) changes are common during the performance of spinal osteotomies in children. The real-time intraoperative information provided by MEPs can provide the necessary information to direct key surgical decisions.

Methods: The neuromonitoring changes occurring during the performance of 37 3-column, cord level, posterior spinal osteotomies in 28 patients were recorded. The procedures were divided, for comparative purposes, into 2 groups based on the presence or absence of alerts. A decrease in somatosensory evoked potentials and transcranial MEPs greater than 50% of baseline was considered an alert. Alerts were classified chronologically as type I: prior to decompression, type II: occurring during decompression and bone resection, type III: occurring after osteotomy closure.

Results: Somatosensory evoked potential alerts occurred in 3 patients, all of whom had significant MEP alerts. There were 2 type I, 15 type II, and 6 type III MEP alerts. Increasing blood pressure improved MEPs in all with the exception of 8 type II and 4 type III. The unresponsive 8 type II alerts were treated with osteotomy closure with the expectation that spinal shortening would decompress the spinal cord and improve spinal cord perfusion. The unresponsive 4 type III alerts all responded to reopening, manipulation, and subsequent reclosure of the osteotomy either with a cage or less correction. There were 5 immediate postoperative motor deficits. No patient had a permanent deficit.

Conclusion: Changes unresponsive to increasing blood pressure occurring during decompression and bone resection (type II) responded well to osteotomy closure. Unresponsive changes during osteotomy closure (type III) were treated successfully with opening the osteotomy, cage adjustment, and less correction.
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April 2013

Remote cardioprotection by direct peripheral nerve stimulation and topical capsaicin is mediated by circulating humoral factors.

Basic Res Cardiol 2012 Mar 10;107(2):241. Epub 2012 Jan 10.

Division of Cardiology, Labatt Family Heart Center, Hospital for Sick Children, Toronto, ON, Canada.

We have previously shown that remote ischemic preconditioning by limb ischemia (rIPC) or intra-arterial adenosine releases a dialyzable cardioprotective circulating factor(s), the release of which requires an intact neural connection to the limb and is blocked by pretreatment with S-nitroso-N-acetylpenicillamine (SNAP). Remote cardioprotection can be induced by other forms of peripheral stimulation including topical capsaicin, but the mechanisms of their signal transduction are incompletely understood. Rabbits were anesthetized by intravenous pentobarbital, intubated and ventilated, then randomized (4-7 animals in each group) to receive sham procedure, rIPC (4 cycles of 5 min lower limb ischemia, 5 min reperfusion), direct femoral nerve stimulation, topical capsaicin, pretreatment with intra-arterial SNAP + capsaicin, pretreatment with topical DMSO (a sensory nerve blocker) + topical capsaicin, or pretreatment with intra-arterial SNAP + femoral nerve stimulation, topical DMSO alone, or intra-arterial SNAP alone. Blood was then rapidly drawn from the carotid artery to produce the plasma dialysate which was used to perfuse a naïve heart from an untreated donor rabbit. The infarct size and recovery of LV-developed pressure and end-diastolic pressure were measured after 30 min of global ischemia and 120 min of reperfusion. Compared to sham, dialysate from rIPC, femoral nerve stimulation, and topical capsaicin groups all produced significant cardioprotection with significantly reduced infarct size, and improved the post-ischemic cardiac performance. Cardioprotection was not seen in the topical DMSO-capsaicin, SNAP + capsaicin, and SNAP + FNS groups. These results confirm the central role of peripheral nerves in the local signal transduction of remote cardioprotection. Direct electrical or peripheral neural stimulation evokes the release of cardioprotective substances into the bloodstream, with comparable effects to that of rIPC induced by limb ischemia.
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March 2012

Neurophysiological changes in deformity correction of adolescent idiopathic scoliosis with intraoperative skull-femoral traction.

Spine (Phila Pa 1976) 2011 Sep;36(20):1627-38

Hospital for the Sick Children, Toronto, Canada.

Study Design: Retrospective review of 36 consecutive patients undergoing coronal plane deformity correction with intraoperative skull-femoral traction between 2005 and 2008 with motor evoked potential (MEP)/somatosensory evoked potential monitoring.

Objective: To determine the prevalence and significance of neurophysiological changes with intraoperative skull-femoral traction in adolescent idiopathic scoliosis.

Summary Of Background Data: Intraoperative skeletal traction can be associated with spinal cord stretching and ischemia with resultant electrophysiological changes. The prevalence and risks of such changes and their clinical significance is unknown.

Methods: Thirty-seven procedures involving 36 patients (27 females and 9 males) with a mean age of 14.8 (12-18) years were divided into two groups on the basis of the presence (group 1, n = 18 procedures) or absence (group 2, n = 19) of significant MEP changes with surgery. They were compared with patients undergoing correction without traction (group 3).

Results: Significant differences among the groups were observed in mean preoperative Cobb angle (86° vs. 70° vs. 59°), mean intraoperative posttraction Cobb angle (50.0° vs. 34.6°), traction index (0.41 vs. 0.50), flexibility index (0.14 vs. 0.27 vs. 0.25), and presence of primary lumbar curves (0% vs. 32% vs. 14%). Initial onset of MEP amplitude loss (group 1) occurred at a mean of 94 (1-257) minutes from the onset of surgery, was bilateral in 13 procedures, and improved at a mean of 5.5 (1-29) minutes after decreasing or removing the traction. At closure, complete bilateral recovery to baseline was observed in 10 procedures, recovery to >50% baseline in five, and recovery to <50% baseline in three procedures. There were no neurologic deficits in this series.

Conclusion: Intraoperative traction is associated with frequent changes in MEP monitoring. The thoracic location of the major curve, increasing Cobb angle, and rigidity of major curve are significant risk factors for changes in MEP with traction. The presence of any MEP recordings irrespective of its amplitude at closure was associated with normal neurological function. Somatosensory evoked potential monitoring did not correlate with the traction induced MEP amplitude changes.
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September 2011

Intraoperative neurophysiological monitoring during complex spinal deformity cases in pediatric patients: methodology, utility, prognostication, and outcome.

Childs Nerv Syst 2010 Apr 7;26(4):523-44. Epub 2010 Mar 7.

Division of Neurosurgery, Hospital for Sick Children, University of Toronto, 555 University Ave, Toronto, ON, Canada.

Introduction: Complex spinal deformity (CSD) problems in pediatric patients result from a wide variety of congenital, acquired, neoplastic, or traumatic abnormalities that result in a combination of spinal deformity and spinal cord impingement. While these problems are rare, decompression, correction, instrumentation, and fusion are quite hazardous. Intraoperative neurophysiological monitoring (IONM) seems particularly beneficial in these patients.

Methodology: Somatosensory evoked potentials, transcranial electrical motor evoked potentials (MEPs), direct waves, and electromyography were used in a variety of CSD cases over a period when IONM was routine for most spinal cases. Examples of cases in which IONM provided important intraoperative information and significantly affected the course of the operation are illustrated.

Results: IONM is a useful tool particularly in CSD cases in pediatric patients but requires special expertise and anesthetic considerations. Loss of MEP appears to have particularly important adverse prognostic information. Conversely, maintenance of IONM provides significant reassurance that the spinal cord function is being maintained. Preserved but persistently diminished MEPs usually predict a neurological injury that will significantly improve and possibly completely recover. Issues concerning training, certification, oversight, standardization of equipment, and technique are partially but incompletely resolved.

Discussion: IONM is an extremely valuable tool for management of CSD pediatric patients. The utility of IONM is such and the detection of unexpected or unanticipated neurological injury frequent enough that a strong argument that it be used in every spinal surgery case can be made.
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April 2010

Stimulation threshold potentials of intraoperative cortical motor mapping using monopolar trains of five in pediatric epilepsy surgery.

Childs Nerv Syst 2010 May 1;26(5):675-9. Epub 2009 Dec 1.

Division of Neurosurgery, The Hospital for Sick Children, University of Toronto, Toronto, Canada.

Objective: Direct cortical stimulation in commonly used for the accurate localization of the motor cortex but the electrical threshold stimulation parameters with this technique had not been fully established.

Patients And Methods: A retrospective review of 15 cases of pediatric surgical cases were performed. The patients consisted of nine male patients and six female patients with age range from 2 to 18 years (mean: 10.8 years; median: 14 years). The most common pathology was cortical dysplasia (nine cases). Stimulation was performed with a train of five stimulations (range five-seven stimulations; <5% of stimulations required more than five stimulations) applied, each train of 50 micros pulse duration, with an interstimulus interval of 1.1 msec. Stimulation intensity commenced at 25 V and this was increased at 5-10 V increments until motor evoked potentials waveforms of sufficient duration and morphology were consistently generated.

Results: Monopolar electrical stimulation threshold for intraoperative motor cortical mapping were found to be more consistent in the upper limb compared to lower limb and facial muscles. Evoked responses from the extensor digitorium communis had the highest recorded rate (83.7%) and required the lowest stimulation voltage (36.0 V). The stimulation voltage was found to be statistically significant compared to threshold values for abductor hallucis, tibialis anterior, deltoid, and orbicularis oris with respective p values of 0.006, 0.021, 0,027, and 0.015. There was also a distinct trend that patients with cortical dysplasia/tuberous sclerosis have higher stimulation thresholds when compared to other pathology (p = 0.067).

Conclusion: Monopolar electrical stimulation threshold for intraoperative motor cortical mapping were more consistent in the upper limb compared to lower limb and facial muscles. Evoked responses from the extensor digitorium communis had the highest recorded rate and required the lowest stimulation voltage. There was also a distinct trend that patients with cortical dysplasia/tuberous sclerosis have higher stimulation thresholds.
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May 2010

Patient with postcentral gyrectomy demonstrates reliable localization of hand motor area using magnetoencephalography.

Pediatr Neurosurg 2009 28;45(4):311-6. Epub 2009 Aug 28.

Division of Neurology, The Hospital for Sick Children, Toronto, Ont., Canada.

Magnetoencephalography (MEG) data analyzed with novel spatial filtering methods, namely event-related beamforming (ERB), have shown success in localizing hand motor areas in healthy adults and in a group of pediatric patients with peri-Rolandic tumors. The validity of this method to localize the primary motor field in a pediatric tumor case was confirmed by intraoperative direct cortical stimulation. Currently, the reliability of this method has not been demonstrated. We report on a 16-year-old boy with localization-related epilepsy originating from his right hemisphere sensory cortex. Hand motor and sensory areas were identified preoperatively by ERB analysis of MEG data. The patient underwent invasive monitoring which localized the epileptic focus to right postcentral gyrus, immediately posterior to the MEG motor area and adjacent to the MEG sensory area. The patient received a gyrectomy of sensory cortex guided by intraoperative direct cortical stimulation to ensure sparing of hand motor cortex. Replication of the MEG motor mapping protocol postoperatively demonstrated reliable localization of the motor and sensory areas. We also discuss caveats for future applications of this protocol.
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May 2010

Facial nerve electromyography: a useful tool in detecting nonauditory side effects of cochlear implantation.

J Otolaryngol Head Neck Surg 2009 Apr;38(2):157-65

Cochlear Implant Program, Department of Otolaryngology, The Hospital for Sick Children and the University of Toronto, Toronto, Ontario.

Background: Facial nerve stimulation is a known complication of cochlear implantation. Until recently, the assessment of facial nerve stimulation was primarily based on self reports which can be problematic in a pediatric setting. For children with facial nerve stimulation, the long-term implications implant use are unclear.

Objectives: To illustrate the clinical utility of facial electromyography (EMG) in avoiding nonauditory stimulation evoked by cochlear implant use and to assess the potential for change in these responses over time with chronic electrical stimulation.

Methods: Midline evoked auditory brainstem responses and surface EMG of the facial musculature were performed in three children suspected clinically of having electrically evoked facial nerve stimulation. Each child had a different clinical presentation; the first complained of pain, the second experienced involuntary facial movements, and the third experienced nonspecific discomfort after sequential bilateral cochlear implantation.

Results: All three children had EMG evidence of facial nerve stimulation. However, based on thresholds and patterns of responses in specific facial nerve branches, stimulation was responsible for the subjective and behavioural responses in only two of the three children.

Conclusions: Pediatric cochlear implant users are unreliable in their reports of facial nerve stimulation. Evoked surface EMG is an objective and useful clinical tool in patients with known or suspected facial nerve stimulation and can lead to improved implant use.
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April 2009

Presurgical localization of primary motor cortex in pediatric patients with brain lesions by the use of spatially filtered magnetoencephalography.

Neurosurgery 2009 Mar;64(3 Suppl):ons177-85; discussion ons186

Department of Diagnostic Imaging, Hospital for Sick Children, Toronto, Canada.

Objective: The objective of this study was to confirm the efficacy of spatially filtered magnetoencephalography for the preoperative localization of primary motor cortex in pediatric patients with focal lesions in the region of the sensorimotor cortex.

Methods: We recorded movement-related magnetoencephalographic activity in 10 pediatric patients (age range, 7-18 years; mean age, 12.5 years) undergoing presurgical evaluation for focal brain lesion resection. Participants made transient movements of the right and left index finger in response to a visual cue. The premovement motor field component in the averaged brain response was localized with a newly developed beamformer spatial filter algorithm. Cortical mapping of motor cortex intraoperatively was conducted in 5 of the 10 patients.

Results: The motor field time-locked to electromyography onset was successfully localized to cortical areas corresponding to the hand region primary motor cortex in 95% of cases (9 of 10 from nonlesional hemisphere; 10 of 10 from lesional hemisphere). Intraoperative electrocortical stimulation activated the expected muscles at motor field coregistered cortical source locations in all cases tested (n = 5). Using these methods, we also found that displacement of the sensorimotor cortex by space-occupying tumors did not interfere with the localization of motor cortex.

Conclusion: We conclude that noninvasive localization of the primary motor cortex can be reliably performed by using spatially filtered magnetoencephalography techniques, which provide a robust and accurate measurement of motor cortical function for the purpose of surgical guidance.
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March 2009

Intraoperative confirmation of hand motor area identified preoperatively by magnetoencephalography.

Pediatr Neurosurg 2008 27;44(4):313-7. Epub 2008 May 27.

Division of Neurology, The Hospital for Sick Children, Toronto, Ont., Canada.

Background: Presurgical functional mapping using magnetoencephalography (MEG) has been performed for somatosensory, auditory and visual functions; however, the traditional analysis method utilizing dipole source analysis has some inherent limitations when applied to the mapping of cortical motor areas. Recently, a novel source reconstruction algorithm [event-related synthetic aperture magnetometry (erSAM)] has demonstrated success for the localization of motor function in healthy adults. We applied this technique to preoperatively map motor function in a young patient. We then confirmed our mapping with direct cortical stimulation intraoperatively.

Methods: This is a case report of an 8-year-old girl with right hand and arm weakness and poor right hand motor control secondary to a left peri-rolandic tumor. Preoperatively, whole-head MEG was recorded while the patient performed a self-paced button pressing task. Cortical activity associated with the onset of movement was localized to the right hand precentral gyrus superior and medial to the tumor using erSAM, while sensory function was localized posterior to the tumor on the postcentral gyrus.

Results: Intraoperative direct cortical stimulation of the motor area identified by MEG resulted in electromyographic activation of intrinsic muscles of the contralateral hand exclusively.

Conclusions: This is the first report of a case where direct cortical stimulation has confirmed a motor cortical location identified by the erSAM method.
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September 2008

Effect of low-dose ketamine on voltage requirement for transcranial electrical motor evoked potentials in children.

Spine (Phila Pa 1976) 2007 Oct;32(22):E627-30

Department of Anesthesia, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.

Study Design: Randomized controlled trial. OBJECTIVE.: To determine the effect of low-dose ketamine on the voltage needed to elicit maximal amplitude of the motor-evoked response to transcranial electrical stimulation during propofol/remifentanil anesthesia in children undergoing scoliosis surgery.

Summary Of Background Data: Motor-evoked potentials (MEPs) are increasingly used to assess the integrity of motor pathways during surgery. Whereas most general anesthetics depress MEP amplitude, the effect of ketamine has been variable, ranging from little or no reduction to an increase in amplitude, suggesting that ketamine may be useful as an agent to facilitate MEP monitoring. We tested the hypothesis that low-dose ketamine would reduce the voltage required to elicit maximal amplitude of the motor-evoked response to transcranial electrical stimulation during propofol/remifentanil anesthesia.

Methods: Thirty-four patients 12 to 16 years of age undergoing posterior instrumentation for correction of idiopathic scoliosis were randomly assigned to receive low-dose ketamine (0.5 mg/kg bolus, followed by 4 microg/kg/min infusion) or an equal volume of saline. Anesthesia was maintained using a mixture of 30% oxygen in air, continuous infusion of propofol at a rate of 100 to 150 microg/kg per min, and continuous infusion of remifentanil. Myogenic motor-evoked responses to transcranial electrical stimulation of the motor cortex were recorded. The minimum voltage required to elicit maximal amplitude of the MEP response was determined. Voltage requirements were compared using the Mann-Whitney U rank sum test. P < 0.05 was considered statistically significant.

Results: No significant difference was found in the minimal voltage needed to elicit maximum amplitude of the MEP response. Median (range) voltage requirements in the ketamine and control groups were 227 V (range, 160-350 V) and 215 V (range, 150-300 V), respectively.

Conclusion: Addition of low-dose ketamine to propofol/remifentanil anesthesia does not significantly reduce the voltage needed to elicit maximum amplitude of the motor-evoked response to transcranial electrical stimulation.
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October 2007