Intraoperative Motor Evoked Potential Monitoring Research Articles

The Improvement of Intraoperative Motor Evoked Potential after Decompression in Cervical Compressive Myelopathy: Its Significance and Related Factors

Objective: This study investigated the relationship between intraoperative motor evoked potential (MEP) improvement after decompression surgery for cervical compressive myelopathy (CCM) and postoperative neurological outcomes, and preoperative factors influencing MEP improvement.Methods: MEP amplitudes were measured prospectively before and after decompression in 38 patients with CCM. The patients were categorized into three groups according to whether the intraoperative MEP slightly decreased, slightly increased, or significantly increased. Functional outcomes were assessed using the recovery rate (RR) and absolute improvement (AI) of the modified Japanese Orthopaedic Association score on postoperative days (PODs) 7 and 28. The preoperative characteristics and intraoperative MEP changes among the three groups were compared. Additionally, the correlation between the increase in MEP amplitude during surgery and the extent of improvement in functional outcomes was investigated.Results: The significantly increased MEP group had a lower baseline MEP amplitude (152.46 µV; p=0.009). In the slightly decreased MEP group, the RR was 27.98 ± 32.29% at POD 7 (p=0.010) and 11.61 ± 69.84% at POD 28 (p=0.200); the AI was 0.79 ± 0.80 at POD 7 (p=0.010) and 0.79 ± 1.42 at POD 28 (p=0.100). In the slightly increased MEP group, the RR was 23.75 ± 28.36% at POD 7 (p=0.040) and 28.47 ± 43.38% at POD 28 (p=0.070); the AI was 1.00 ± 1.21 at POD 7 (p=0.030) and 1.08±1.88 at POD 28 (p=0.100). In the significantly increased MEP group, the RR was 41.06 ± 32.01% at POD 7 (p=0.009) and 59.78 ± 34.52% at POD 28 (p=0.006); the AI was 3.08 ± 2.07 at POD 7 (p=0.009) and 4.33 ± 2.54 at POD 28 (p=0.006). Greater intraoperative MEP improvement correlated with better postoperative recovery at 1 month (RR, p=0.010; AI, p<0.001).Conclusion: Intraoperative MEP monitoring is valuable for predicting postoperative neurological outcomes in CCM patients, particularly those with lower baseline MEP amplitudes. Significant intraoperative MEP improvements are associated with better functional recovery. These findings underscore the importance of MEP monitoring in optimizing surgical strategies and predicting neurological recovery.

Updated review on the use of neuromuscular blockade during intraoperative motor-evoked potential monitoring in the modern anesthesia era.

Transcranial electrical stimulation motor-evoked potentials (Tc-MEP) monitoring is a common practice in neurosurgery to prevent postoperative neurological damage. However, the use of neuromuscular blocking agents (NMBAs) during Tc-MEP monitoring is a subject of controversy. In addition, the effectiveness of sugammadex, a selective reversal agent, in the context of Tc-MEP monitoring requires further investigation. This review aimed to clarify the considerations involved in achieving optimal Tc-MEP monitoring while ensuring patient safety. Preoperative patient selection, comorbidity assessment, motor power evaluation, and the nature of the planned surgery are critical factors. Accurate paralysis assessment, continuous NMBA infusion, and post-tetanic stimulation techniques are essential for achieving optimal partial NMB. The decision to administer an NMB during Tc-MEP monitoring necessitates a careful evaluation of the balance between accuracy and potential complications. This review emphasizes the challenges associated with NMB administration during Tc-MEP monitoring and highlights the need for personalized patient assessment.

Total Intravenous Anesthesia Protocol for Decreasing Unacceptable Movements during Cerebral Aneurysm Clipping with Motor-Evoked Potential Monitoring: A Historical Control Study and Meta-Analysis.

Injury can occur during intraoperative transcranial motor-evoked potential (MEP) monitoring caused by patient movement related to insufficient neuromuscular blocking agent use. Here, we evaluated the incidence of unacceptable movements in patients undergoing intraoperative MEP monitoring following our anesthetic protocol. We reviewed the anesthesia records of 419 patients who underwent unruptured cerebral aneurysm clipping with intraoperative MEP monitoring. The anesthetic protocol included target-controlled infusion with a fixed effect-site propofol concentration of 3 μg/mL and an adjustable effect-site remifentanil concentration of 10-12 ng/mL. We compared our findings of the intraoperative parameters and incidence of spontaneous movement and respiration with those of published meta-analysis studies. Spontaneous movement and respiration occurred in one (0.2%) patient each. The meta-analysis included six studies. The pooled proportions of spontaneous movement and respiration were 6.9% (95% confidence interval [CI], 1.3-16.5%) and 4.1% (95% CI, 0.5-14.1%), respectively. The proportion of spontaneous movement in our study was significantly lower than that in previous studies (p = 0.013), with no significant difference in spontaneous respiration (p = 0.097). Following our center's anesthesia protocol during cerebral aneurysm clipping resulted in a low incidence of spontaneous respiration and movement, indicating its safety for patients undergoing intraoperative MEP monitoring.

Motor Evoked Potential

Motor evoked potential(MEP)is the most widely used intraoperative neurophysiological monitoring measure. It includes cortical direct stimulation MEP(dMEP), which directly stimulates the primary motor cortex of the frontal lobe identified by short-latency somatosensory evoked potentials, and transcranial MEP(tcMEP), which involves high-current or high-voltage transcranial stimulation using cork-screw electrodes installed in the scalp. dMEP is performed in brain tumor surgery close to the motor area. tcMEP is simple, safe, and widely used in spinal and cerebral aneurysm surgeries. The increase in sensitivity and specificity with compound muscle action potential(CMAP)after peripheral nerve stimulation normalization performed in MEP to remove the effect of muscle relaxants is unclear. However, tcMEP for decompression in compressive spinal and spinal nerve diseases may predict the recovery of postoperative neurological symptoms with CMAP normalization. The anesthetic fade phenomenon can be avoided with CMAP normalization. The cutoff rate of loss of amplitude that causes postoperative motor paralysis in intraoperative MEP monitoring is 70%-80%, and setting an alarm at each facility based on this is necessary.

Transcranial versus direct electrical stimulation for intraoperative motor-evoked potential monitoring: Prognostic value comparison in asleep brain tumor surgery.

ObjectiveSafe resection of gliomas involving motor pathways in asleep-anesthesia requires the combination of brain mapping, to identify and spare essential motor sites, and continuous monitoring of motor-evoked potentials (MEPs), to detect possible vascular damage to the corticospinal tract (CST). MEP monitoring, according to intraoperative neurophysiology societies, is generally recommended by transcranial electrodes (TES), and no clear indications of direct cortical stimulation (DCS) or the preferential use of one of the two techniques based on the clinical context is available. The main aim of the study was to identify the best technique(s) based on different clinical conditions, evaluating the efficacy and prognostic value of both methodologies.MethodsA retrospective series of patients with tumors involving the motor pathways who underwent surgical resection with the aid of brain mapping and combined MEP monitoring via TES and DCS was evaluated. Irreversible MEP amplitude reduction (>50% compared to baseline) was used as an intraoperative warning and correlated to the postoperative motor outcome. Selectivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were computed for both techniques.ResultsFour hundred sixty-two patients were retrospectively analyzed, and only 1.9% showed a long-term motor impairment. Both TES and DCS obtained high specificity and NPV for the acute and 1-month motor deficit. Sensitivity was rather low for the acute deficit but excellent considering the 1-month follow-up for both techniques. DCS was extremely reliable in predicting a postoperative motor decline (PPV of 100% and 90% for acute and long-term deficit, respectively). Conversely, TES produced a high number of false-positive results, especially for long-term deficits (65, 87.8% of all warnings) therefore obtaining poor PPV values (18% and 12% for acute and 1-month deficits, respectively). TES false-positive results were significantly associated with parietal tumors and lateral patient positioning.ConclusionsData support the use of mapping and combined monitoring via TES and DCS. The sole TES monitoring is reliable in most procedures but not in parietal tumors or those requiring lateral positioning. Although no indications are available in international guidelines, DCS should be recommended, particularly for cases approached by a lateral position.

Successful recording of direct cortical motor-evoked potential from a pediatric patient under remimazolam anesthesia: a case report

BackgroundIntraoperative motor-evoked potential (MEP) monitoring reduces postoperative motor deficits. Propofol-based total intravenous anesthesia is the gold standard for intraoperative myogenic MEPs. Although there is no contraindication to administering propofol in adults with peanut, soy, or egg allergies, its safety in children with these allergies remains unclear.Case presentationA 12-year-old girl required general anesthesia under intraoperative direct cortical MEP (dc-MEP) monitoring due to supratentorial glioma. Remimazolam-based anesthesia was selected, instead of propofol, due to the patient’s egg hypersensitivity. Stable myogenic MEPs were recorded throughout the surgery with remimazolam at 0.9 mg/kg/h and remifentanil at 0.35 μg/kg/min, following adjustments of stimulation intensity and titration of remimazolam infusion. Neither intraoperative memory nor motor deficits were present after surgery.ConclusionsWe present a pediatric case whose dc-MEP was recorded under remimazolam anesthesia. The cardiovascular stability and avoidance of propofol infusion syndrome with remimazolam were superior to propofol.

Intraoperative motor and somatosensory evoked potential monitoring during surgical clipping of ruptured and unruptured intracranial aneurysms: a comparative study.

The current study investigated the correlation between intraoperative motor evoked potential (MEP) and somatosensory evoked potential (SSEP) monitoring and both short-term and long-term motor outcomes in aneurysm patients treated with surgical clipping. Moreover, the authors provide a relatively optimal neurophysiological predictor of postoperative motor deficits (PMDs) in patients with ruptured and unruptured aneurysms. A total of 1017 patients (216 with ruptured aneurysms and 801 with unruptured aneurysms) were included. Patient demographic characteristics, clinical features, intraoperative monitoring data, and follow-up data were retrospectively reviewed. The efficacy of using changes in MEP/SSEP to predict PMDs was assessed using binary logistic regression analysis. Subsequently, receiver operating characteristic curve analysis was performed to determine the optimal critical value for duration of MEP/SSEP deterioration. Both intraoperative MEP and SSEP monitoring were significantly effective for predicting short-term (p < 0.001 for both) and long-term (p < 0.001 for both) PMDs in aneurysm patients. The critical values for predicting short-term PMDs were amplitude decrease rates of 57.30% for MEP (p < 0.001 and area under the curve [AUC] 0.732) and 64.10% for SSEP (p < 0.001 and AUC 0.653). In patients with an unruptured aneurysm, the optimal critical values for predicting short-term PMDs were durations of deterioration of 17 minutes for MEP (p < 0.001 and AUC 0.768) and 21 minutes for SSEP (p < 0.001 and AUC 0.843). In patients with a ruptured aneurysm, the optimal critical values for predicting short-term PMDs were durations of deterioration of 12.5 minutes for MEP (p = 0.028 and AUC 0.706) and 11 minutes for SSEP (p = 0.043 and AUC 0.813). The authors found that both intraoperative MEP and SSEP monitoring are useful for predicting short-term and long-term PMDs in patients with unruptured and ruptured aneurysms. The optimal intraoperative neuromonitoring method for predicting PMDs varies depending on whether the aneurysm has ruptured or not.

Intraoperative motor-evoked potential monitoring during coil embolization for anterior choroidal artery aneurysms

Intraoperative motor-evoked potential (MEP) monitoring is widely used in the neck clipping of cerebral aneurysms. Little is known regarding the usefulness of intraoperative MEP monitoring in endovascular aneurysm surgery. The purpose of this study was to validate the feasibility of intraoperative MEP monitoring during the coil embolization of anterior choroidal artery (AChA) aneurysms. Clinical and angiographic data of consecutive patients who underwent coil embolization for unruptured AChA aneurysms with or without intraoperative MEP monitoring between January 2014 and December 2018 at our institute were abstracted and analyzed retrospectively. Twenty-three unruptured AChA aneurysms were treated. Eleven patients received MEP monitoring, and three of them experienced intraoperative reduction or disappearance of the MEP wave. Even during MEP changes, AChA filling showed no change in any of the three cases. Although one case with MEP monitoring encountered the disappearance of AChA filling, there was no change in MEP. This might be due to retrograde filling of the AChA from the anastomosis with the lateral posterior choroidal artery. AChA blood flow detected by angiography did not always reflect MEP status. When comparing the presence or absence of MEP monitoring, the volume embolization ratio of coiled aneurysms was significantly better in the MEP group. Intraoperative MEP monitoring during endovascular coiling for AChA aneurysms may be feasible. AChA blood flow detected by angiography does not always reflect MEP status.

Feasibility of intraoperative motor evoked potential monitoring during tethered cord surgery in infants younger than 12 months

PurposeFeasibility, reliability, and safety assessment of transcranial motor evoked potentials (MEPs) in infants less than 12 months of age.MethodsA total of 22 patients with a mean age of 33 (range 13–49) weeks that underwent neurosurgery for tethered cord were investigated. Data from intraoperative MEPs, anesthesia protocols, and clinical records were reviewed. Anesthesia during surgery was maintained by total intravenous anesthesia (TIVA).ResultsMEPs were present in all patients for the upper extremities and in 21 out of 22 infants for the lower extremities. Mean baseline stimulation intensity was 101 ± 20 mA. If MEPs were present at the end of surgery, no new motor deficit occurred. In the only case of MEP loss, preoperative paresis was present, and high baseline intensity thresholds were needed. MEP monitoring did not lead to any complications. TIVA was maintained with an average propofol infusion rate of 123.5 ± 38.2 µg/kg/min and 0.46 ± 0.17 µg/kg/min for remifentanil.ConclusionIn spinal cord release surgery, the use of intraoperative MEP monitoring is indicated regardless of the patient’s age. We could demonstrate the feasibility and safety of MEP monitoring in infants if an adequate anesthetic regimen is applied. More data is needed to verify whether an irreversible loss of robust MEPs leads to motor deficits in this young age group.

Bilateral C5 Palsy Following A Circumferential Surgery for Cervical Spondylotic Myelopathy: A Case Report and Review

Background and Importance: The development of C5 root palsy is a well-known potential complication of cervical spine surgeries for the correction of cervical spondylotic myelopathy. It typically occurs unilaterally, but on extremely rare occasions, bilaterally. The value of intraoperative neurophysiologic monitoring in detecting iatrogenic acute versus delayed onset C5 palsy, the rarity of bilateral C5 palsy, and its optimal management require further discussion. Case Presentation: A 49-year-old woman with quadriparesis due to cervical spondylotic myelopathy is presented. She underwent circumferential 360° cervical spine surgery. This operation was subsequently complicated by a delayed bilateral C5 palsy, despite normal transcranial motor evoked potentials (MEPs). With the utilization of conservative treatment, the complete resolution of this complication took roughly eight months. Conclusion: Bilateral C5 palsy is an infrequent consequence of multilevel cervical spine surgeries. Although intraoperative monitoring of transcranial electrical stimulation-induced MEPs has high sensitivity and specificity in foreseeing the acute-onset C5 palsy, it cannot predict delayed-onset palsy. Including the current case, only seven cases have been reported in the medical literature. Overall, conservative management in adherence to rigorous physical therapy may be an acceptable treatment.

243. Should somatosensory evoked potentials and motor evoked potentials monitoring be routinely used in all posterior cervical operations for degenerative conditions of the cervical spine?

<h3>BACKGROUND CONTEXT</h3> Posterior decompression with or without instrumented fusion (PCF) are some of the most common procedures undertaken by spine surgeon. PCF can be the preferred approach for treating patients with cervical spinal traumatic fractures, degenerative spondylosis, deformity tumors, infection and vascular malformations. Intraoperative monitoring is helpful during cases where direct or indirect manipulation of the cord is expected. However, whether neuromonitoring is necessary in routine PCF surgery for degenerative cervical spine conditions remains unknown. <h3>PURPOSE</h3> Here we evaluate the utility of somatosensory evoked potential (SSEP) and motor evoked potential (MEP) monitoring as a tool for predicting postoperative neurologic deficits during PCF for degenerative cervical spine conditions. <h3>STUDY DESIGN/SETTING</h3> Retrospective review of prospectively collected clinical data. <h3>PATIENT SAMPLE</h3> This study included 498 patients who underwent posterior cervical operations for degenerative conditions of the cervical spine, excluding indications such as tumor, trauma, deformity, vascular lesions, and infection. <h3>OUTCOME MEASURES</h3> Sensory and motor neurologic deficit postoperatively. <h3>METHODS</h3> We retrospectively reviewed cases in which PCF was performed for a variety of cervical spine conditions at our institute over a 5-year period. SSEP monitoring was performed in all patients with MEP monitoring performed in only a subset of patients. Patients who had neurologic deficits postoperatively were then identified and detailed analysis was performed to ascertain whether SSEP or MEP monitoring accurately predicted onset of postoperative deficits. The sensitivity, specificity and predictive value of each monitoring paradigm was then determined. <h3>RESULTS</h3> We retrospectively evaluated clinical outcomes and intraoperative monitoring data in 757 patient and identified 498 patients who underwent posterior cervical operations for degenerative conditions of the cervical spine, excluding indications such as tumor, trauma, deformity, vascular lesions, and infection. Forty percent were female, 60% were male with ages ranging from 22 to 93 years-old (mean 67 years-old). SSEP were monitored for all 498 patients during surgery (121 patients [24.3%] had both MEP and SSEP monitoring). Twenty-one patients (4.2%) had neurological deficits after surgery in this cohort. SSEP monitoring had a higher specificity and sensitivity than MEP monitoring for detecting neurologic compromise intraoperatively in PCF cases (91% vs 79% and 60% vs 20% respectively). The positive (PPV) and negative predictive values (NPV) of SSEP monitoring in picking up intraoperative changes that translated to postoperative neurologic deficit were 30% and 97% respectively whereas PPV and NPV of MEP monitoring were 6% and 96% respectively. <h3>CONCLUSIONS</h3> Taken together, these data suggest that intraoperative SSEP and MEP monitoring during PCF is not reliable at predicting postoperative neurologic deficits. With their relatively high NPV, however, MEP and more so SSEP are useful to provide peace of mind intraoperatively when no abnormalities are detected. Thus, use of SSEP and MEP monitoring in PCF should only be limited to cases where the risk of postoperative neurologic deficit is high. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Effects of polarity of bipolar sensorimotor direct cortical stimulation on intraoperative motor evoked potentials

ObjectiveThe present study investigated the effects of the stimulus polarity and location of motor evoked potential (MEP) to establish a stimulation protocol. MethodsNineteen patients who intraoperatively underwent MEP in bipolar direct cortical stimulation were enrolled in the present study. Somatosensory evoked potentials (SEP) of the contralateral median nerve stimulation were recorded to determine stimulation sites. MEP was performed under two settings in all patients: 1. Anodal bipolar stimulation: an anode on the precentral gyrus and a cathode on the postcentral gyrus, 2. Cathodal bipolar stimulation: a cathode on the precentral gyrus and an anode on the postcentral gyrus. MEP amplitudes and the coefficient of variation (CV) at a stimulation intensity of 25 mA and the thresholds of induced MEP were compared between the two settings. ResultsAn electrical stimulation at 25 mA induced a significantly higher amplitude in cathodal bipolar stimulation than in anodal bipolar stimulation. Cathodal bipolar stimulation also showed significantly lower thresholds than anodal stimulation. CV did not significantly differ between the two groups. ConclusionsThese results indicate that cathodal bipolar stimulation is superior to anodal bipolar stimulation for intraoperative MEP monitoring. SignificanceMEP in cathodal bipolar cortical stimulation may be used in a safe and useful evaluation method of motor fiber damage that combines sensitivity and specificity.

WS5.2. Intraoperative Monitoring of Motor Evoked Potentials: Physiology and Applications

Intraoperative monitoring (IOM) of motor evoked potentials (MEP) represents a significant advance for evaluation of descending motor tract integrity. For spinal decompression, there is increasing evidence of its efficacy, but ongoing research is performed to improve sensitivity and specificity. To that end, there is also ongoing debate for warning criteria of MEP changes from transcranial electrical stimulation (TES). It is presently unclear if a cutoff for ensuing neurological deficit should be MEP disappearance or a value between this and 50% amplitude reduction. Interim adjunctive strategies include use of ipsilateral MEPs, modified scalp stimulating positions and multimodality monitoring. Some investigators have proposed a more directed motor threshold to obtain supramaximal MEP voltage in an individual subject. The indications of MEP monitoring have expanded from spinal surgery to central nervous system procedures involving cortical, subcortical and brainstem regions. Corticobulbar MEPs can provide localization and evaluate functional integrity of cranial nerve nuclei. Awake craniotomy can combine monopolar MEP mapping with other modalities to preserve speech and motor functions. The evidence of MEP monitoring for scoliosis to date has been encouraging for the prevention of neurological compromise, as a result of deformity correction. IOM of MEPs is pertinent here as a non-invasive surgical adjunct for these neurologically intact patients. Recently, a study has suggested that in susceptible individuals, intraoperative suppression of MEPs may rarely occur unpredictably, independent of surgical or anesthetic intervention, but anesthetic factors may be overall more significant. Side effects of TES are rare, but seizures, bite injury, lip laceration, mandibular fracture, scalp burns and cardiac complications should be anticipated. Improved knowledge in the use of intravenous anesthetic agents and pulse train cortical stimuli has allowed for more efficacious MEP monitoring. However, recent studies suggest that often, suboptimal MEPs were elicited, especially during IOM of diseased spinal cord. Various central and peripheral facilitatory techniques will be discussed.

Improved potential quality of intraoperative transcranial motor-evoked potentials by navigated electrode placement compared to the conventional ten-twenty system

Intraoperative neurophysiological monitoring of transcranial motor-evoked potentials (tcMEPs) may fail to produce a serviceable signal due to displacements by mass lesions. We hypothesize that navigated placement of stimulation electrodes yields superior potential quality for tcMEPs compared to the conventional 10–20 placement. We prospectively included patients undergoing elective cranial surgery with intraoperative monitoring of tcMEPs. In addition to electrode placement as per the 10–20 system, an electrode pair was placed at a location corresponding to the hand knob area of the primary motor cortex (M1) for every patient, localized by a navigation system during surgical setup. Twenty-five patients undergoing elective navigated surgery for intracranial tumors (n = 23; 92%) or vascular lesions (n = 2; 8%) under intraoperative monitoring of tcMEPs were included between June and August 2019 at our department. Stimulation and recording of tcMEPs was successful in every case for the navigated electrode pair, while stimulation by 10–20 electrodes did not yield baseline tcMEPs in two cases (8%) with anatomical displacement of the M1. While there was no significant difference between baseline amplitudes, mean potential quality decreased significantly by 88.3 µV (− 13.5%) for the 10–20 electrodes (p = 0.004) after durotomy, unlike for the navigated electrodes (− 28.6 µV [− 3.1%]; p = 0.055). For patients with an anatomically displaced M1, the navigated tcMEPs declined significantly less after durotomy (− 3.6% vs. 10–20: − 23.3%; p = 0.038). Navigated placement of tcMEP electrodes accounts for interindividual anatomical variance and pathological dislocation of the M1, yielding more consistent potentials and reliable potential quality.

Effects of Preoperative Motor Status on Intraoperative Motor-evoked Potential Monitoring for High-risk Spinal Surgery: A Prospective Multicenter Study.

Prospective multicenter observational study. To evaluate transcranial motor-evoked potentials (Tc-MEPs) baseline characteristics of lower limb muscles and to determine the accuracy of Tc-MEPs monitoring based on preoperative motor status in surgery for high-risk spinal disease. Neurological complications are potentially serious side effects in surgery for high-risk spine disease. Intraoperative spinal neuromonitoring (IONM) using Tc-MEPs waveforms can be used to identify neurologic deterioration, but cases with preoperative motor deficit tend to have poor waveform derivation. IONM was performed using Tc-MEPs for 949 patients in high-risk spinal surgery. A total of 4454 muscles in the lower extremities were chosen for monitoring. The baseline Tc-MEPs was recorded immediately after exposure of the spine. The derivation rate was defined as muscles detected/muscles prepared for monitoring. A preoperative neurological grade was assigned using the manual muscle test (MMT) score. The 949 patients (mean age 52.5 ± 23.3 yrs, 409 males [43%]) had cervical, thoracic, thoracolumbar, and lumbar lesions at rates of 32%, 40%, 26%, and 13%, respectively. Preoperative severe motor deficit (MMT ≤3) was present in 105 patients (11%), and thoracic ossification of the posterior longitudinal ligament (OPLL) was the most common disease in these patients. There were 32 patients (3%) with no detectable waveform in any muscles, and these cases had mostly thoracic lesions. Baseline Tc-MEPs responses were obtained from 3653/4454 muscles (82%). Specificity was significantly lower in the severe motor deficit group. Distal muscles had a higher waveform derivation rate, and the abductor hallucis (AH) muscle had the highest derivation rate, including in cases with preoperative severe motor deficit. In high-risk spinal surgery, Tc-MEPs collected with multi-channel monitoring had significantly lower specificity in cases with preoperative severe motor deficit. Distal muscles had a higher waveform derivation rate and the AH muscle had the highest rate, regardless of the severity of motor deficit preoperatively.Level of Evidence: 3.

Motor-evoked potentials in the intraoperative decision-making of circumferential decompression via posterior approach for treating thoracic posterior longitudinal ligament ossification

Surgical treatment is indicated for symptomatic thoracic ossification of posterior longitudinal ligament (OPLL), and circumferential decompression (CD) is a promising option. However, the risk of postoperative paralysis in ventral decompression of CD is as high as 30%. Therefore, it is important to balance surgical outcomes and safety of ventral decompression. To investigate the role of intraoperative motor-evoked potential (MEP) changes in decision-making of one-staged CD via posterior approach for treating thoracic OPLL. A retrospective cohort analysis PATIENT SAMPLE: Twenty-five thoracic OPLL patients in this study underwent posterior decompression (PD) alone, and the other 21 patients accepted CD. Intraoperative MEP monitoring from both abductor hallucis and tibialis anterior, and modified Japanese Orthopaedic Association (mJOA) scores. MEPs were recorded in all patients before and after PD, and patients accepting CD underwent further MEP recordings after ventral decompression. According to MEP changes after PD, patients were divided into MEP improvement, MEP deterioration and no MEP change. Postoperative MEP improvement rates were measured in all tested muscles. Additionally, all patients accepted mJOA scores before and 2 years after operation. Patients in both CD and PD groups exhibited improved mJOA scores after operation (p<.05), and both mJOA and MEP improvement rates were similar between these two groups (p>.05). In no MEP change group, patients accepting CD exhibited increased mJOA improvement rates compared with those accepting PD (p<.05). In MEP deterioration group, higher mJOA improvement rates were observed in PD group than in CD group (p<.05). In MEP improvement group, mJOA improvement rates were similar between CD and PD groups (p>.05). Both CD and PD can effectively treat thoracic OPLL, and which of these two strategies can achieve better functional recovery may be related to different MEP changes after PD. Therefore, monitoring MEP changes may provide additional references in decision-making of one-staged CD for treating thoracic OPLL.

Cervical schwannoma in the early stage of pregnancy: a case report

BackgroundAlthough spinal schwannomas generally grow very slowly, it has been reported that these clinical growths and their associated neurological symptoms accelerate during pregnancy. Because these cases are rare, surgical intervention for this tumor during pregnancy poses a significant challenge. The change of pregnancy-related hormones, such as estrogen and progesterone, is considered to have an effect on the clinical symptoms of spinal tumors. Expressions of the receptors for estrogen and progesterone in orbital and vestibular schwannomas have been reported; however, those expressions in spinal schwannomas have not been examined.Case presentationA 36-year-old woman at 8 weeks' gestation suffered from developing neck pain and neurological symptoms in the right upper extremity. Magnetic resonance imaging (MRI) confirmed the presence of a cervical intradural extramedullary tumor. Under general anesthesia, using intraoperative neurophysiological monitoring of motor-evoked potentials (MEPs), spinal tumor resection following a hemi-laminoplasty was performed in a prone position at 12 weeks gestation. The pathological diagnosis following surgery was spinal schwannoma. Her neurological symptoms were significantly improved after surgery and she delivered a healthy baby in her 40th week of pregnancy. At a 12-month follow-up, no abnormalities were observed during medical examinations of both mother and child. An immunohistochemical study identified the expression of estrogen receptors, but not progesterone receptors, in the spinal schwannoma.ConclusionsA cervical spinal schwannoma was successfully removed under general anesthesia at 12 weeks gestation by coordination between orthopaedic, obstetric and anesthesia teams. For the first time, an immunohistochemical analysis showed that the expression of estrogen receptors was identified in spinal schwannoma cells, suggesting the possibility that these hormone receptors in spinal schwannoma might contribute to the worsening of neurological symptoms during pregnancy.

경두개 전기자극을 이용한 경추 수술 중 횡격막 신경의 감시: 증례 보고

To prevent phrenic nerve injuries during surgery, intraoperative monitoring has been used increasingly. Intraoperative monitoring comprises stimulation of phrenic nerves in the neck and getting compound motor action potential (CMAP) in the diaphragm. However, in high cervical lesions or in surgeries that need particular positions such as a prone position, the usage could be limited due to a difficulty in stimulating the phrenic nerve directly. To solve these problems, we tried motor evoked potential (MEP) via transcranial electrical stimulation to a diaphragm during cervical tumor resection. The monitoring revealed relatively constant MEP graphs of the diaphragm during the monitoring, and we did not notice any decrement of more than 50% in the amplitude. Sequentially, the patient recovered without any weakness or remarkable respiration rate changes which could suggest any phrenic nerve injuries. Our case supports that intraoperative MEP monitoring to diaphragm could be feasible in cases with difficulty in stimulating the phrenic nerve directly.

Motor evoked potential monitoring can evaluate ischemic tolerance to carotid artery occlusion during surgery.

Balloon test occlusion (BTO) is a useful examination for evaluating ischemic tolerance to internal carotid artery (ICA) occlusion. The aim of this study was to investigate the relationships between intraoperative motor evoked potential (MEP) monitoring and the results of preoperative BTO. Between 2013 and 2017, 32 patients undergoing surgery under general anesthesia with intraoperative MEP monitoring, in whom preoperative BTO was performed, were identified. A receiver operator characteristic (ROC) analysis was performed to determine the appropriate cutoff value of MEP amplitude for BTO-positive. Furthermore, the accuracy of MEP monitoring for BTO-positive was compared with electroencephalogram (EEG) and somatosensory evoked potential (SEP) monitoring. Four of 32 (12.5%) patients were BTO-positive. The cutoff value of MEP amplitude for BTO-positive was a > 80% reduction from the baseline level, which showed sensitivity of 100% and specificity of 100%. Thus, the sensitivity and specificity for BTO-positive were significantly higher for MEP than for EEG (100% and 72.0%, p = 0.02) in 28 patients, but they were not significantly different compared with SEP (33.3% and 100%, p = 0.48) in 21 patients. MEP monitoring might be one of the alternatives for evaluating ischemic tolerance to ICA occlusion during surgery. The cutoff value of MEP amplitude was a > 80% reduction.

A novel effective paradigm of intraoperative electrical stimulation mapping in children.

Resective epilepsy surgery is an established treatment method for children with focal intractable epilepsy, but the use of this method introduces the risk of postsurgical motor deficits. Electrical stimulation mapping (ESM), used to define motor areas and pathways, frequently fails in children. The authors developed and tested a novel ESM protocol in children of all age categories. The ESM protocol utilizes high-frequency electric cortical stimulation combined with continuous intraoperative motor-evoked potential (MEP) monitoring. The relationships between stimulation current intensity and selected presurgical and surgery-associated variables were analyzed in 66 children (aged 7 months to 18 years) undergoing 70 resective epilepsy surgeries in proximity to the motor cortex or corticospinal tracts. ESM elicited MEP responses in all children. Stimulation current intensity was associated with patient age at surgery and date of surgery (F value = 6.81, p < 0.001). Increase in stimulation current intensity predicted postsurgical motor deficits (F value = 44.5, p < 0.001) without effects on patient postsurgical seizure freedom (p > 0.05). The proposed ESM paradigm developed in our center represents a reliable method for preventing and predicting postsurgical motor deficits in all age groups of children. This novel ESM protocol may increase the safety and possibly also the completeness of epilepsy surgery. It could be adopted in pediatric epilepsy surgery centers.