Successful Motor Evoked Potential Monitoring in Cervical Myelopathy : Related Factors and the Effect of Increased Stimulation Intensity

ObjectiveIntraoperative neurophysiological monitoring (IONM) has been widely used during spine surgery to reduce or prevent neurologic deficits, however, its application to the surgical management for cervical myelopathy remains controversial. This study aimed to assess the success rate of IONM in patients with cervical myelopathy and to investigate the factors associated with successful baseline monitoring and the effect of increasing the stimulation intensity by focusing on motor evoked potentials (MEPs). MethodsThe data of 88 patients who underwent surgery for cervical myelopathy with IONM between January 2016 and June 2018 were retrospectively reviewed. The success rate of baseline MEP monitoring at the initial stimulation of 400 V was investigated. In unmonitorable cases, the stimulation intensity was increased to 999 V, and the success rate final MEP monitoring was reinvestigated. In addition, factors related to the success rate of baseline MEP monitoring were investigated using independent t-test, Wilcoxon rank-sum test, chi-squared test, and Fisher’s exact probability test for statistical analysis. The factors included age, sex, body mass index, diabetes mellitus, smoking history, symptom duration, Torg-Pavlov ratio, space available for the cord (SAC), cord compression ratio (CCR), intramedullary increased signal intensity (SI) on magnetic resonance imaging, SI length, SI ratio, the Medical Research Council (MRC) grade, the preoperative modified Nurick grade and Japanese Orthopedic Association (JOA) score. ResultsThe overall success rate for reliable MEP response was 52.3% after increasing the stimulation intensity. No complications were observed to be associated with increased intensity. The factors related to the success rate of final MEP monitoring were found to be SAC (p<0.001), CCR (p<0.001), MRC grade (p<0.001), preoperative modified Nurick grade (p<0.001), and JOA score (p<0.001). The cut-off score for successful MEP monitoring was 5.67 mm for SAC, 47.33% for the CCR, 3 points for MRC grade, 2 points for the modified Nurick grade, and 12 points for the JOA score. ConclusionIncreasing the stimulation intensity could significantly improve the success rate of baseline MEP monitoring for unmonitorable cases at the initial stimulation in cervical myelopathy. In particular, the SAC, CCR, MRC grade, preoperative Nurick grade and JOA score may be considered as the more important related factors associated with the success rate of MEP monitoring. Therefore, the degree of preoperative neurological functional deficits and the presence of spinal cord compression on imaging could be used as new detailed criteria for the application of IONM in patients with cervical myelopathy.     

运动诱发电位联合体感诱发电位监测在脊髓髓内肿瘤手术中的应用

目的 探讨全静脉麻醉下运动诱发电位(MEP)联合体感诱发电位(SEP)术中监测应用于脊髓髓内肿瘤手术的优越性、可靠性及临床应用价值.方法 对72例脊髓髓内肿瘤患者术中行SEP和MEP联合监测,参照McCormick评分标准对术前、术后脊髓功能的改变和诱发电位变化之间的关系进行统计分析.结果 14例脊髓神经功能改善,18例术后脊髓神经功能下降者与诱发电位监测结果具有一致性(P＜0.05).结论 对脊髓髓内肿瘤手术进行SEP与MEP监测有利于避免"假阴性/假阳性"结果及术后神经功能障碍的发生.     

多模式神经电生理监测辅助显微手术治疗椎管内肿瘤的疗效分析

目的探讨多模式神经电生理检测下显微手术切除椎管内肿瘤的临床疗效。方法回顾性分析2011年5月至2016年6月显微手术切除的椎管内肿瘤57例,术中采用体感诱发电位(SEP)、运动诱发电位(MEP)及肌电图(EMG)多模式神经电生理监测(MIOM)。结果肿瘤全切49例(86.0%),次全切除6例(10.5%),部分切除2例(3.5%),失访4例,53例术后随访3个月~2年,神经功能改善45例(78.9%),无明显改善4例(12.3%),症状加重3例(7.0%),复发1例(1.8%)。结论多模式神经电生理检测辅助显微手术切除椎管内肿瘤,能有效提高肿瘤全切率,并预测和保护脊髓神经功能,提高手术疗效及安全性。     

Successful intraoperative spinal cord monitoring during scoliosis surgery using a total intravenous anesthetic regimen including dexmedetomidine

Intraoperative neurophysiological monitoring (IONM) during corrective spinal surgery is widely used. Because of the possible interference with the recording of evoked potentials by inhalational anesthetics, total intravenous anesthetic (TIVA) regimens have been advocated. TIVA regimens may be difficult to use in pediatric populations due to metabolic factors. We report on the results of multimodality IONM during 18 cases in which a TIVA regimen incorporating dexmedetomidine (Precedex, Hespira, Lake Forest, IL) was used. Monitoring techniques included sensory (SSEP) and motor evoked potentials (MEP), as well as pedicle screw stimulation. SSEPs were maintained within an acceptable range of baseline amplitude (50%) and latency (10%), and MEPs remained elicitable throughout each case. We therefore found that the anesthetic regimen did not significantly interfere with any of the monitoring modalities used and conclude that IONM in the presence of dexmedetomidine is feasible under appropriate conditions.     

Predictors of functional outcome after spinal cord surgery: Relevance of intraoperative neurophysiological monitoring combined with preoperative neurophysiological and MRI assessments

ObjectivesTo assess the accuracy of intraoperative neurophysiological monitoring (IONM) in predicting immediate and 3-month postoperative neurological new deficit (or deterioration) in patients benefiting from spinal cord (SC) surgery; and to identify factors associated with a higher risk of postoperative clinical worsening.MethodsConsecutive patients who underwent SC surgery with IONM were included. Pre and postoperative clinical (modified McCormick scale), radiological (lesion-occupying area ratio), and electrophysiological features were collected.ResultsA total of 99 patients were included: 14 (14.1%) underwent extradural surgery, 50 (50.5%) intradural extramedullary surgery, and 35 (35.4%) intramedullary surgery. Cumulatively, multimodal IONM (motor and somatosensory evoked potentials, D-wave whenever possible) significantly predicted postoperative deficits (p<0.001), with a sensitivity, specificity, positive predictive value, and negative predictive value of 0.81, 0.93, 0.83, and 0.92, respectively. Sixty (60.6%) patients displayed no IONM change, whereas 39 (39.4%) displayed IONM worsening. In multivariate analysis, predictors for postoperative clinical worsening were: abnormal preoperative electrophysiological assessment (p=0.03), intramedullary tumor (p<0.001), lesion-occupying area ratio ≥0.7 (p<0.001), and IONM alterations (p<0.001). Three months after the surgical procedure, in patients presenting at least one of the risk factors described above, 45/81 (55.6%) and 19/81 (23.5%) were clinically and electrophysiologically improved, respectively; while 13/81 (16.0%) and 10/81 (12.3%) were clinically and electrophysiologically worsened.ConclusionMultimodal IONM is an essential tool to guide SC surgery, and enables the accurate prediction of postoperative neurological outcome. Specific attention should be given to patients presenting with preoperative electrophysiological abnormalities, large tumor volume, and intramedullary tumor location.     

Relationship between the states of spinal impact injuries and magnetically evoked EMGs in rats

Abstract

The relationship between the states of spinal Impact injuries and magnetically evoked electromyograms (EMGs) were studied in rats. Impact injuries to the spinal cord were induced at a depth of 0.25-2.0 mm by insertion of a cylinder tip measuring 2 mm in diameter into the lumbar vertebrae L1-L2. Magnetically induced electromyograms for the brain and lumbar vertebrae L4-L5 were recorded from the tibialis anticus and the gastrocnemius muscles. H-reflex was not induced by the spinal cord injury (SCI) at a depth of 0.25 mm, although motor evoked potential (MEP) was observed. Continuous waves following the M- response were observed in the SCI at a depth of 0.25 mm. Elevation of the threshold, reduction of its latency and decrease in amplitude of the M-responses were observed at an injury depth of 0.5 mm or deeper. With SCI magnitude from mild (0.5 mm depth) to severe (1.0 mm depth), the amplitudes of the M-response were decreased, and the latency of the M-response was shorter than that of the control. The F-response was accelerated in severe SCI. Our results indicated that there was a relationship between extensive injury legions and the H-reflex F- and M-responses in magtnetically evoked EMGs. Magnetically evoked EMGs are useful for monitoring the states of SCI. [Neurol Res 2000; 22: 727-732]     

Intraoperative neurophysiological monitoring (IONM): lessons learned from 32 case events in 2069 spine cases

Intraoperative neurophysiological monitoring (IONM) is becoming the standard of care for many spinal surgeries, especially those with deformity correction and instrumentation. We reviewed 2069 spine cases with multimodality IONM including somatosensory evoked potentials (SSEP), transcranial electrical motor evoked potentials (TCeMEP), and spontaneous and triggered electromyography (s-EMG and t-EMG) in a University setting over a period of four years to examine perioperative clinical findings when an IONM event was noted and to ascertain how IONM has affected our ability to avoid potential neurological injury during spine surgery. We performed a retrospective analysis of cases from 2006 to 2010 to study the frequency and cause of intraoperative events detected via IONM and the clinical outcome of the patient. There were 32 cases (1.5%) with possible intraoperative events. There were 17 (53%) cases where IONM changes affected the course of the surgery and prevented possible postoperative neurological deficits. Seven cases (41%) were due to deformity correction, five (29%) due to hypotension, four (24%) due to patient positioning, and one (6%) due to a screw requiring repositioning. None of the 17 patients had postoperative motor or sensory deficits. There were four cases with false-positive IONM findings due to correctible technical issues. Three cases required surgical revision due to pedicle screw malposition. In each case, s-EMGs failed to exhibit intraoperative changes but the patient presented with postoperative radiculopathy. We believe that the use of t-EMGs may have prevented these complications. This review reinforces the importance of multimodality IONM for spinal surgery. The incidence of possible events in our series was 1.5%, and several likely postoperative neurologic deficits were avoided by intraoperative intervention.     

多模式神经电生理监测在脊柱手术中的应用

目的：用多模式的神经电生理检测包括体感诱发电位（SEP）、运动诱发电位（MEP）、肌电图（EMG）,以及肌松剂四联刺激肌肉收缩试验（TOF）对脊柱手术监测进行研究,探究检查的方法和对报警的判断。方法：用多模式神经电生理监测方法对120例不同类型脊柱手术进行监测。结果：术中报警67例（63．3％）,其中SEP报警46．7％,MEP报警19．1％,EMG报警35．0％。术后均无严重的并发症,并且及时发现了1例术后的血肿压迫并及时予以将其清除。结论：多模式神经电生理监测能最大程度地有效降低脊柱手术的风险。     

神经电生理监测技术在圆锥马尾病变手术中的应用

目的探讨神经电生理监测技术在圆锥马尾病变手术中应用价值。方法回顾性分析110例圆锥马尾病变患者临床资料,其显微外科手术均在神经电生理监测下进行,感觉诱发电位(somatosensory evoked potential,SEP)和运动诱发电位(motor evoked potential,MEP)监测脊髓功能,肌电图(electromyography,EMG)确定肿瘤切除范围。结果显微镜下病变全切除92例(83.6%),次全或大部分切除18例(16.4%)。术后随访1~58个月,神经系统查体及JOA评分发现脊髓神经功能改善102例(92.8%),无变化4例(3.6%),下降4例(3.6%)。对病变切除前与切除后SEP潜伏期和波幅以及MEP潜伏期进行自身比较,脊髓神经功能改善和下降患者电生理监测指标改变差异有统计学意义(P0.05),脊髓神经功能无变化患者相关监测指标改变差异无统计学意义(P0.05),神经电生理监测指标的变化与术后脊髓神经功能改善情况基本相吻合。结论术中神经电生理监测可以实时了解脊髓神经功能的完整性,结合显微神经外科技术可以明显提高圆锥马尾病变的全切率,减少术后并发症,提高手术疗效及安全性。     

Significance and usefulness of corticospinal motor evoked potential monitoring for lesions adjacent to primary motor cortex]

This study evaluated the usefulness of intraoperative corticospinal motor evoked potential (MEP) monitoring in preventing postoperative motor deficits, and whether this procedure contributed to surgery on intrinsic brain lesions in the vicinity of the motor area. The subjects were 45 patients with brain tumors located in and around the primary motor area. MEP was recorded through the cervical epidural electrodes in response to stimulation of the motor cortex. The amplitude of D-response of MEP was compared at the beginning and at the end of surgery. Then MEP changes were divided into five groups; "increase", "no change", "diminish", "decrease" and "disappear". We used the DeJong classification for qualitative analysis of motor function, and reviewed these findings in relation to the change in MEP. It was possible to record MEP when the preoperative motor weakness was DeJong 3 or better. There was no postoperative motor deficit when the MEP amplitude was preserved at better than 50% of a control amplitude. If the amplitude decreased to less than 50%, motor deficits were encoutered. When MEP amplitude increased during the surgery, preoperative motor weakness was improved after the surgery. It is concluded that there is little possibility of causing motor deficits even if tumor removal is aggressively pursued, as long as the amplitude of D-response remains at 50% or more of the baseline. This monitoring procedure is expected to improve the overall surgical results in patients with intrinsic brain tumors around the motor area.     

Diagnostic accuracy of evoked potentials for functional impairment after contusive spinal cord injury in adult rats

Iatrogenic spinal cord injury (SCI) is a cause of potentially debilitating post-operative neurologic complications. Currently, intra-operative neurophysiological monitoring (IONM) via somatosensory evoked potentials and motor-evoked potentials is used to detect and prevent impending SCI. However, no empirically validated interventions exist to halt the progression of iatrogenic SCI once it is detected. This is in part due to the lack of a suitable translational model that mimics the circumstances surrounding iatrogenic SCI detected via IONM. Here, we evaluate a model of simulated contusive iatrogenic SCI detected via IONM in adult female Sprague-Dawley rats. We show that transient losses of somatosensory evoked potentials responses are 88.24% sensitive (95% confidence interval [CI] 63.53–98.20) and 80% specific (95% CI 51.91–95.43) for significant functional impairment following simulated iatrogenic SCI. Similarly, we show that transient losses in motor-evoked potentials responses are 70.83% sensitive (95% CI 48.91–87.33) and 100% specific (95% CI 62.91–100.00) for significant functional impairment following simulated iatrogenic SCI. These results indicate that our model is a suitable replica of the circumstances surrounding clinical iatrogenic SCI.     

Estimate of motor conduction in human spinal cord: slowed conduction in spinal cord injury

By using motor evoked potential (MEP) created by transcranial electric stimulation over the motor cortex and F-wave measurement from the peripheral nerve stimulation, it is possible to estimate the spinal cord motor conduction velocity (SCMCV) in the diseased state. Twenty-four patients with spinal cord injury (SCI) between T1 and T11 neurological levels participated in this study. MEP in leg muscle was absent in all neurologically complete paraplegics. In 16 patients with neurologically incomplete SCI, MEP was obtained in 13 patients. The SCMCV estimated from C7 to T12 spinal levels was 32.1 (SD = 9.4) m/s. This was significantly slower than 63.3 (SD = 8.6) m/s in 40 normal controls. This noninvasive, indirect method is measurable, and can provide valuable electrophysiological data in the assessment of motor function in patients with SCI.     

Intraoperative Neurophysiology Monitoring for Spinal Dysraphism

Spinal dysraphism often causes neurological impairment from direct involvement of lesions or from cord tethering. The conus medullaris and lumbosacral roots are most vulnerable. Surgical intervention such as untethering surgery is indicated to minimize or prevent further neurological deficits. Because untethering surgery itself imposes risk of neural injury, intraoperative neurophysiological monitoring (IONM) is indicated to help surgeons to be guided during surgery and to improve functional outcome. Monitoring of electromyography (EMG), motor evoked potential, and bulbocavernosus reflex (BCR) is essential modalities in IONM for untethering. Sensory evoked potential can be also employed to further interpretation. In specific, free-running EMG and triggered EMG is of most utility to identify lumbosacral roots within the field of surgery and filum terminale or non-functioning cord can be also confirmed by absence of responses at higher intensity of stimulation. The sacral nervous system should be vigilantly monitored as pathophysiology of tethered cord syndrome affects the sacral function most and earliest. BCR monitoring can be readily applicable for sacral monitoring and has been shown to be useful for prediction of postoperative sacral dysfunction. Further research is guaranteed because current IONM methodology in spinal dysraphism is still deficient of quantitative and objective evaluation and fails to directly measure the sacral autonomic nervous system.     

Intraoperative neurophysiologic monitoring for intramedullary spinal-cord tumor surgery

During resection of intramedullary spinal-cord tumors intraoperative neurophysiological monitoring has become a true surgical technology. Motor evoked potentials are the most important modality for this purpose. Its use requires neurophysiological expertise from the surgeon, and a monitoring team in place able to handle the necessary equipment. Motor potentials are evoked by transcranial electrical motor cortex stimulation. A "single stimulus technique" evokes D-waves recorded from the spinal cord. The "multipulse (or train) stimulation technique" evokes electromyographic responses in peripheral muscles. These are optimally recorded from the thenar, hypothenar, tibialis anterior, and flexor hallucis brevis muscles, which are known to have strong pyramidal innervation. D-wave monitoring looks primarily at the peak-to-peak amplitude. When monitoring muscle MEPs, the presence or absence of the response irrespective of stimulation intensity is the important parameter. Preparations for neurophysiological monitoring fit quite well into a neurosurgical operating room environment. Recording and interpretation of MEPs is fast and straightforward. Pre- and postoperative clinical motor findings correlate with intraoperative MEP results. Thus correct prediction of the clinical status at a given time during surgery is possible with a very high certainty. The sensitivity of muscle MEPs for postoperative motor deficits is nearly 100%, its specificity is about 90%. Thus MEP data indeed reflect the clinical "reality". Present and stable recordings document intact motor pathways and allow the surgeon to confidently proceed with a tumor resection. Loss of muscle MEPs and/or decrease of the D-wave amplitude constitutes a "window of warning". It reflects a pattern of MEP change indicating a reversible injury to the essential motor pathways. Using this information, the surgical strategy can be adapted before irreversible neurological damage is caused by the surgical manipulation. Such adaptation comprises simply waiting for the recordings to spontaneously improve again, irrigating with warm saline solution to wash out blocking potassium. Other measures include the elevation of mean arterial pressure to improve local perfusion. Even staged resection can be considered if intraoperative measures do not sufficiently improve the recordings.     

不完全性脊髓缺血损伤动物模型的建立及价值

目的 探讨不完全性脊髓缺血损伤动物模型的建立方法,为不完全性脊髓缺血损伤机制研究提供理想的载体. 方法 24只新西兰大白兔按照随机数字表法分为对照组及3根组、4根组,每组8只.对照组用于排除麻醉和手术对运动诱发电位的影响;3根组、4根组分别结扎3根、4根腰动脉.各组麻醉后记录基线诱发电位,手术/结扎后30 min、2d、7d记录诱发电位;麻醉清醒后、手术/结扎后2d、7d进行运动功能评分;手术/结扎后7d后取缺血中心区标本进行HE染色,镜下观察. 结果 3根组动物结扎后30 min诱发电位波幅与对照组比较差异有统计学意义(P＜0.05),结扎后2d、7d与对照组比较差异无统计学意义(P＞0.05);4根组动物结扎后30 min、2d、7d3个时间点诱发电位波幅与对照组比较差异均有统计学意义(P＜0.05).3组动物手术/结扎后30min、2d、7d3个时间点的潜伏期与对照组比较差异均无统计学意义(P＞0.05).各组动物运动功能评分结果与诱发电位波幅变化一致. 结论 结扎3根腰动脉可以造成可逆性不完全性脊髓缺血损伤,结扎4根腰动脉可以造成不可逆性不完全性脊髓缺血损伤.     

Relationship between the states of spinal impact injuries and magnetically evoked EMGs in rats

The relationship between the states of spinal impact injuries and magnetically evoked electromyograms (EMGs) were studied in rats. Impact injuries to the spinal cord were induced at a depth of 0.25-2.0 mm by insertion of a cylinder tip measuring 2 mm in diameter into the lumbar vertebrae L1-L2. Magnetically induced electromyograms for the brain and lumbar vertebrae L4-L5 were recorded from the tibialis anticus and the gastrocnemius muscles. H-reflex was not induced by the spinal cord injury (SCI) at a depth of 0.25 mm, although motor evoked potential (MEP) was observed. Continuous waves following the M-response were observed in the SCI at a depth of 0.25 mm. Elevation of the threshold, reduction of its latency and decrease in amplitude of the M-responses were observed at an injury depth of 0.5 mm or deeper. With SCI magnitude from mild (0.5 mm depth) to severe (1.0 mm depth), the amplitudes of the M-response were decreased, and the latency of the M-response was shorter than that of the control. The F-response was accelerated in severe SCI. Our results indicated that there was a relationship between extensive injury legions and the H-reflex F- and M-responses in magnetically evoked EMGs. Magnetically evoked EMGs are useful for monitoring the states of SCI.     

颅内前循环动脉瘤术中诱发电位监测效果评估

目的 探讨全静脉麻醉下经颅电刺激运动诱发电位(TES-MEPs)联合体感诱发电位(SEP)监测颅内前循环动脉瘤手术及预防缺血性卒中的应用价值.方法 47例颅内动脉瘤夹闭手术患者,术中行SEP和TES-MEPs联合监测,以神经功能检查作为评价指标,比较术前和术后神经功能的改变和诱发电位变化之间的关系.结果 43例神经功能未见显著改变,4例神经功能出现不同程度下降,其中3例MEP及SEP同时出现波幅下降＞50%或消失,且手术结束时未恢复至基线水平,与术后神经功能障碍发生具有一致性.结论 术中监测指标的改变可较早地获得脑缺血的证据,联合SEP与MEP监测有利于降低术后缺血性脑卒中的发生.     

EEG oscillations and magnetically evoked motor potentials reflect motor system excitability in overlapping neuronal populations

ObjectiveTo understand the relationship between neuronal excitability reflected by transcranial magnetic stimulation (TMS) evoked motor potentials (MEPs) and spontaneous oscillation amplitude and phase.MethodsWe combined spontaneous EEG measurement with motor cortex TMS and recorded MEP amplitudes from abductor digiti minimi (ADM).ResultsMidrange-beta oscillations over the stimulated left motor cortex were, on average, weaker before large- than small-amplitude MEPs. The phase of occipital midrange-beta oscillations was related to the MEP amplitudes.ConclusionsThe present results support the view that MEP and Rolandic beta oscillation amplitudes are associated with motor cortical excitability. However, oscillations seen in EEG reflect the excitability of a large population of cortical neurons, and MEP amplitude is affected also by spinal excitability and action potential desynchronization. Thus, MEP and EEG oscillation amplitudes are not strongly correlated. In addition, even during rest, motor system excitability appears to be related to activity in occipital areas at frequency ranges associated with visuomotor processing.SignificanceThe ability of spontaneous oscillations and MEPs to inform us about cortical excitability is clarified. For example, it is suggested that oscillatory activity at non-motor sites might be related to motor system excitability at rest.     

Intraoperative thalamocortical tract monitoring via direct cortical recordings during craniotomy

ObjectiveNeuromonitoring of primary motor regions allows preservation of motor strength and is frequently employed during cranial procedures. Less is known about protection of sensory function and ability to modulate movements, both of which rely on integrity of thalamocortical afferents (TCA) to fronto-parietal regions. We describe our experience with TCA monitoring and their cortical relays during brain tumor surgery.MethodologyTo study its feasibility and usefulness, continuous somatosensory evoked potentials (SSEP) recording via a subdural electrode was attempted in 32 consecutive patients.ResultsMedian and posterior tibial SSEP were successfully monitored in 31 and 17 patients respectively. SSEP improved lesion localization and prevented unnecessary cortical stimulation in 9 and 16 cases respectively. A threshold of ≥30% SSEP amplitude decrease influenced management in 10 patients while a decrement of ≥50 % had a sensitivity of 0.89 and specificity of 1 in detecting worsening of sensory function. Simultaneous motor evoked potentials (MEP) and SSEP monitoring were performed in 10 cases, 9 of which showed short-lived fluctuations of the former.ConclusionDirect cortical SSEP monitoring is feasible, informs management and predicts outcome.SignificanceEarly intervention prevents sensory deficit. Concomitant MEP fluctuations may reflect modulation of motor activity by TCA.     

Direct cortical stimulation with cylindrical depth electrodes in the interhemispheric fissure for leg motor evoked potential monitoring

ObjectiveTo evaluate cylindrical depth electrodes in the interhemispheric fissure as an alternative to subdural strip electrodes for direct cortical stimulation (DCS) leg motor evoked potential (MEP) monitoring.MethodsA cylindrical depth electrode was positioned in the interhemispheric fissure of 37 patients who underwent supratentorial brain surgery. Leg sensory and motor cortices were localized by highest tibial nerve somatosensory evoked potential amplitude and lowest DCS leg MEP threshold; the lowest-threshold electrode was then used for DCS leg MEP monitoring.ResultsIntraoperative leg MEPs were obtained from all the patients in the series. The mean intensity applied for leg MEP monitoring with the cylindrical depth electrode was 15.2 ± 4.0 mA. No complications secondary to neurophysiological monitoring were detected.ConclusionsLower extremity MEPs were consistently recorded using a multi-contact cylindrical depth electrode in the interhemispheric fissure by DCS.SignificanceCylindrical depth electrodes may be a safe and effective alternative for DCS in the interhemispheric fissure, where subdural strips are difficult to place.