MEP Monitoring Research Articles

Characterization of Contusive Spinal Cord Injury by Monitoring Motor-Evoked Potential.

The objective of the study is to characterize the onset and progression of contusive SCI over an eight-week period using a clinically applicable tool in an in vivo model. The background highlights the importance of a reliable and reproducible injury model and assessment tools for SCI. The methods section describes the experimental setup, including randomly assigned rats in three groups: Sham, Control, and Injury (undergoing a moderate contusive SCI using the NYU-Impactor). MEP monitoring and BBB examinations are conducted at baseline and weekly for eight weeks post-injury. The results indicate that the relative MEP power spectral decreased to 11% and 22% in the left and right hindlimbs, respectively, during the first week post-SCI. In the second week, a slight spontaneous recovery was observed, reaching 17% in the left and 31% in the right hindlimbs. Over the following four weeks post-SCI, continuing deterioration of MEP signal power was observed with no detectable recovery. SCI attenuates hindlimb MEP power spectral and reduces locomotion, though the changes in MEP and locomotion exhibit distinct temporal patterns. The MEP monitoring provides valuable insights into the functional integrity of motor pathways following SCI and offer a sensitive and reliable assessment. By implementing MEP monitoring, researchers can track the progression of SCI and evaluate the efficacy of therapeutic interventions quantitatively.

Transcranial MEPs predict clinical outcome during minimally invasive dorsal decompression for cervical spondylotic myelopathy

ObjectivesMotor evoked potential (MEP) monitoring is a reliable method for real-time assessment of corticospinal tract integrity. However, the potential benefits of MEP monitoring during degenerative spine surgery remain controversial. This study aims to determine the role of MEP monitoring during surgery for cervical spondylotic myelopathy (CSM) in prediction of prognosis. MethodsTranscranial electrical stimulation was performed to elicit MEPs during dorsal decompression for the treatment of CSM. MEP-threshold levels were assessed separately at the beginning and end of the surgery in upper extremity muscles corresponding to nerve roots at the level of/distal to the decompression site. Clinical outcome was measured using the modified Japanese Orthopedic Association score (mJOA). ResultsThe study included 47 patients. 31 patients (66 %) showed improvements in neurological function at discharge. A measurable improvement in the majority of tested muscles, or in at least one muscle group, in a given patient highly correlated with mJOA score increase at discharge (p < 0.001) with an odds ratio of 10.3 (CI:2.6–34.4) and 11.4 (CI:2.8–41.3), respectively. Conversely, MEP deterioration was not associated with worse clinical outcome, nor was it predictive of failure to recover. ConclusionMEP improvement during CSM surgery seems to be highly predictive of early postoperative neurological recovery and could indicate subclinically enhanced signal conduction. This highlights the potential of MEP monitoring as an intraoperative, real-time predictive tool for clinical recovery after decompression in patients with CSM.

Which patients do we need to consider augmentation of muscle active potentials regarding transcranial electrical stimulation motor-evoked potentials monitoring before spine surgery?

BACKGROUND CONTEXTTranscranial electrical stimulation motor-evoked potentials (Tc-MEPs) are the current trend and are important in preventing intraoperative neurological deficits. Posttetanic Tc-MEPs (p-MEP) can augment the amplitudes of compound muscle active potentials (CMAPs), especially in the case of insufficient conventional Tc-MEPs (c-MEP). PURPOSETo retrospectively investigate pre- and intraoperative factors necessitating p-MEP monitoring and to examine changes in the success rates of baseline Tc-MEP monitoring before and after tetanic stimulation in patients with such factors. STUDY DESIGNRetrospective observational study. PATIENT SAMPLEPatients (n=184) who underwent spinal surgery with Tc-MEP monitoring in our department between August 2020 and July 2022. OUTCOME MEASURESManual muscle testing (MMT) scores were calculated to identify patients with preoperative motor deficits. c-MEP and p-MEP amplitudes were recorded from the defined muscles. METHODSWe compared preoperative and intraoperative factors between the c-MEP and p-MEP groups (study 1). In cases where the factors were identified, we investigated the success rate of the baseline MEP measurement of each muscle before and after tetanic stimulation (study 2). RESULTSOne hundred fifty-seven patients were included. Of those, 87 showed sufficient CMAPs with c-MEP. Meanwhile, 70 needed p-MEP because of insufficient CMAPs. In univariate analysis, cervical/thoracic surgery (p<.001), preoperative MMT 3 or below (p=.009), shorter duration of illness (p=.037), previous cerebrovascular disease (p=.014), and dialysis (p=.031) were significantly associated with p-MEP group. Preoperative MMT 3 or below was the only factor requiring p-MEP (odds ratio, 3.34; 95% confidence interval, 1.28-8.73, p=.014) in multivariate analysis. In the p-MEP group, 24 patients had preoperative motor deficits; 16 patients with complete data were included in the analysis (study 2). The success rates of MEP monitoring before and after tetanic stimulation of the entire lower-extremity muscles were 42.7 and 57.3%, respectively (p<.001). The success rates for each muscle before and after tetanic stimulation were abductor pollicis brevis: 81.3% and 96.9%, tibialis anterior: 34.4% and 50.0%, gastrocnemius: 25% and 40.6%, and abductor hallucis: 68.8% and 81.3%, respectively. No significant differences were observed in success rates for any of the muscles. CONCLUSIONSPatients with preoperative MMT 3 or below highly needed p-MEP. The success rate of baseline MEP monitoring increased with tetanic stimulation, even in patients with preoperative motor deficits. We believe that p-MEP monitoring can result in reliable CMAP recording, especially in cases of preoperative motor deficits with MMT scores of 3 or below.

Feasibility of multimodal intraoperative neurophysiological monitoring for extramedullary spinal cord tumor surgery in elderly patients

Background/purposeExtramedullary spinal cord tumors (EMSCTs) are mostly benign tumors which are increasingly diagnosed and operatively treated in the elderly. While there are hints that multimodal intraoperative neurophysiological monitoring (IONM) could be influenced by age and age-related comorbidities, no study has ever systematically evaluated its feasibility and value for EMSCT surgery in elderly patients.MethodsWe retrospectively evaluated all patients with microsurgical EMSCT resection under continuous multimodal IONM with SSEPs, MEPs and electromyography between 2016 and 2020. Epidemiological, clinical, imaging and operative/IONM records as well as detailed individual outcomes were analyzed and compared for the cohort < / ≥ 65 years.ResultsMean age was 45 years in cohort < 65 years (n = 109) and 76 years in cohort ≥ 65 years (n = 64), while baseline/operative characteristics did not significantly differ. Mean baseline SSEPs’ latencies (left–right average) were significantly higher in the cohort ≥ 65 years for both median (20.9 ms vs. 22.1 ms; p < 0.01) and tibial nerve (42.9 ms vs. 46.1 ms; p < 0.01) without significant differences for SSEPs’ amplitudes. Stimulation intensity to elicit intraoperative MEPs was significantly higher in the cohort ≥ 65 years (surrogate-marker: left–right-averaged quotient ID1-muscle/abductor-hallucis-muscle; 1.6 vs. 2.1; p < 0.001). Intraoperatively, SSEP and MEP monitoring were feasible in 99%/100% and 99%/98% for the cohort < / ≥ 65 years without significant differences in rates for significant IONM changes during surgery or postoperatively new sensorimotor deficits. Sensitivity of IONM was 29%/43%, specificity 99%/98%, positive and negative predictive values 67%/75% and 95%/93% for the cohort < / ≥ 65 years. Overall, age was no risk factor for IONM feasibility or rate of significant IONM changes.DiscussionMultimodal IONM is feasible/reliable for EMSCT surgery in elderly patients. An age-related prolongation of SSEPs’ latencies and demand for higher stimulation intensities for MEPs’ elicitation has to be considered.

Perspective: Triple intraoperative neurophysiological monitoring (IONM) should be considered the standard of care (SOC) for performing cervical surgery for ossification of the posterior longitudinal ligament (OPLL).

Triple Intraoperative Neurophysiological Monitoring (IONM) should be considered the standard of care (SOC) for performing cervical surgery for Ossification of the Posterior Longitudinal Ligament (OPLL). IONM's three modalities and their alerts include; Somatosensory Evoked Potentials (SEP: =/> 50% amplitude loss; =/>10% latency loss), Motor Evoked Potentials (MEP: =/> 70% amplitude loss; =/>10-15% latency loss), and Electromyography (loss of EMG, including active triggered EMG (t-EMG)). During cervical OPLL operations, the 3 IONM alerts together better detect intraoperative surgical errors, enabling spine surgeons to immediately institute appropriate resuscitative measures and minimize/avoid permanent neurological deficits/injuries. This focused review of the literature regarding cervical OPLL surgery showed that SEP, MEP, and EMG monitoring used together better reduced the incidence of new nerve root (e.g., mostly C5 but including other root palsies), brachial plexus injuries (i.e., usually occurring during operative positioning), and/or spinal cord injuries (i.e., one study of OPLL patients documented a reduced 3.79% incidence of cord deficits utilizing triple IONM vs. a higher 14.06% frequency of neurological injuries occurring without IONM). Triple IONM (i.e., SEP, MEP, and EMG) should be considered the standard of care (SOC) for performing cervical OPLL surgery. However, the positive impact of IONM on OPLL surgical outcomes critically relies on spinal surgeons' immediate response to SEP, MEP, and/or EMG alerts/significant deterioration with appropriate resuscitative measures to limit/avert permanent neurological deficits.

446 Utility of Intraoperative Motor-Evoked Potential in L4-5 Lateral Lumbar Interbody Fusion: 3-Year Prospective Study

INTRODUCTION: Nerve injury has been reported as high as 23% in direct transpsoas lateral interbody fusion (LLIF), particularly at L4-5. METHODS: This is a prospective, observational, cohort study of consecutive patients who underwent L4-5 LLIF in a 3-year interval from 2018 to 2020. Spontaneous and triggered EMG, somatosensory evoked potentials (SSEP) were routinely recorded. In addition MEPs from quadriceps and anterior tibialis muscle groups were also recorded bilaterally. Transcranial MEP were recorded every 5 minutes from the time of incision. A decrease in amplitude of 50% or more from baseline was considered a positive result, and the surgeon was alerted accordingly. Patient’s neurological exam and health related quality of life measures were collected preoperatively, immediately postoperatively, and at the time of follow up at 6 weeks, 3 months, 6 months, 1 and 2 years. RESULTS: 72 patients were included. Transient quadriceps weakness occurred in 13 patients but resolved by 6 weeks. 30 patients had a significant decrease in MEP amplitude without changes in spontaneous or triggered EMG and SSEP. Two patients had persistent dorsiflexion weakness (3/5 and 1/5) at 2 year follow up. One patient had persistent quadriceps (4-/5) and dorsiflexion (4/5) weakness at 1 year follow up. One patient the surgery was aborted at the time of introduction of retractor due to 69% reduction in MEP and inability to mitigate the changes. All instances of MEP changes were noted during retraction phase. No patient with a negative MEP developed weakness postoperatively. At predetermined level of 50% decrease of amplitude, MEP was 100% sensistive and 65% specific in detecting neural injury. CONCLUSION: MEP monitoring provides additional value to sEMG, tEMG, and SSEP during LLIF at L4-5 to avoid injury. The value of MEP is primarily during maintenance of retraction and not during traversing the psoas muscle where EMG is most valuable.

SY5.2. Intraoperative monitoring and mapping during brain tumor surgery

The aggressive removal of a glioma is expected to improve long-term patient survival and quality of life. However, removal of a supratentorial glioma, particularly in proximity to the eloquent cortex, poses a great risk of creating new functional deficits. Thus, it is critical to consider functional and oncological outcomes simultaneously when treating patients with supratentorial glioma. Neurophysiological intraoperative monitoring (NIOM) has long been regarded as the “gold standard” for glioma resection, allowing for maximal resection of lesions while preserving sensorimotor function. NIOM during surgery involves the use of both mapping and monitoring strategies with multiple modalities. Brain mapping is necessary due to individual variability in cortical organization and the unexpected displacement of normal anatomic landmarks by tumor growth. Typically, the median somatosensory evoked potential phase reversal technique is used to localize the central sulcus, followed by direct cortical stimulation with a monopolar electrode and multipulse train stimulation, to confirm the location of the eloquent motor cortex. During resection, motor and somatosensory evoked potentials (MEP and SSEP) from the contralateral hemibody and direct waves (d waves), if indicated, are monitored to safeguard the integrity of functional structures. If resection extends beyond the cortical boundary, subcortical mapping can be used to confirm the approximate distance from the resection cavity to the corticospinal tract. Concomitant use of subcortical mapping and MEP monitoring is believed to be associated with more extensive resection and fewer severe late functional deficits. In addition, a meta-analysis indicated that use of intraoperative brain mapping during glioma surgery resulted in a 2-fold reduction of long term neurological deficits. Further, this was not at the expense of extent of resection. In conclusion, while functional deficits are still possible even with NIOM during the surgical procedure, in most cases, the use of this technique significantly improves patient outcomes.

Feasibility and diagnostic accuracy of intra-operative monitoring of motor evoked potentials in children

This study documents the monitorability using different anesthesia regimes and accuracy of muscle motor evoked potentials (mMEPs) in children ≤2 years of age undergoing tethered cord surgery (TCS). Intraoperative mMEP monitoring was attempted in 100 consecutive children, ≤2 years of age, undergoing TCS. MEP monitoring was done under 4 different anesthetic regimes: (Total intravenous anesthesia (TIVA); balanced anesthesia with sevoflurane and ketamine; balanced anesthesia with isoflurane and ketamine; and balanced anesthesia with sevoflurane). Factors analyzed for their effect on monitorability were: age, neurological deficits, type of anesthesia, and the number of pulses used for stimulation. Baseline mMEPs were obtained in 87% children. Monitorability of mMEPs was similar in children ≤1 year and 1-2 years of age (85.7% and 87.5%). In multivariate analysis, anesthesia regime was the only significant factor predicting presence of baseline mMEPs. Children undergoing TIVA (p=0.02) or balanced anesthesia with a combination of propofol, sevoflurane, and ketamine (p=0.05) were most likely to have baseline mMEPs. mMEPs had a sensitivity of 97.4%, specificity of 96.4%, negative predictive value of 98.2% and accuracy of 96.8%. Baseline mMEPs were obtained in >85% of children ≤2 years of age including those who had motor deficits. TIVA and balanced anesthesia with sevoflurane and ketamine are ideal for mMEP monitoring. mMEPs have a high accuracy although, false positive and false negative results can occasionally be experienced.

Intraoperative responses of motor evoked potentials to the novel intravenous anesthetic remimazolam during spine surgery: a report of two cases

BackgroundRemimazolam is a novel short-acting benzodiazepine characterized by metabolism independent from organ function. We report intraoperative MEP responses of two patients who underwent spine surgery under general anesthesia using remimazolam.Case presentationIn case 1, MEP monitoring was successfully performed with the use of a fixed dose of remimazolam at 0.5 mg/kg/h and remifentanil at 0.2 μg/kg/min. In case 2, an increasing dose of remimazolam from 0.5 to 1.5 mg/kg/h during the operation did not affect MEP signals. In both cases, remimazolam was titrated to maintain the values of entropy electroencephalogram (EEG) monitoring at 40–60.ConclusionsGeneral anesthesia using remimazolam and remifentanil can be a valuable alternative for spine surgery with MEP monitoring by EEG to assess the optimal dose.

Intraoperative Lumbar Muscle Motor Evoked Potential Monitoring With Transcortical Stimulation

Stimulating electrodes for lower extremity motor-evoked potential (LE-MEP) monitoring with transcortical stimulation are usually placed on the medial side of motor cortex convexity, which is not lower extremity but lumbar motor area. Lumbar MEP may be elicited with lower stimulation intensity than LE-MEP through this location, and it is useful to monitor lower extremity motor function intraoperatively. Intraoperative lumbar and LE-MEP monitoring with transcortical stimulation during surgery of 12 patients with lesions involving the motor cortex from January 2012 to February 2019 at Shinshu University Hospital were reviewed retrospectively. Stimulations were delivered by a train of 5 pulses of anodal constant current stimulation. Stimulating electrode position was determined by motor cortex mapping. Recording needle electrodes were placed on bilateral lumbar muscles and contralateral leg muscles. The threshold-level stimulation method was used for MEP monitoring. The thresholds, monitoring result, and postoperative motor function of lumbar and lower extremities were compared. The mean baseline thresholds were 19.9 ± 8.9 mA for lumbar MEP and 26.5 ± 11.5 mA for LE-MEP (P= 0.02). Patterns of intraoperative monitoring changes were the same between lumbar and LE-MEP monitoring. Lumbar MEP was stimulated with lower stimulation intensity than the LE-MEP with the same intraoperative pattern of waveform changes in 12 patients. Lumbar MEP monitoring may be useful for preserving the corticospinal tract of lower extremities intraoperatively.

전정신경초종 수술 중 얼굴 운동유발전위 추적감시의 유용성: 증례

전정신경초종 수술 중 얼굴 운동유발전위 추적감시의 유용성: 증례

Scoliosis in chronic neuronopathic Gaucher disease: Characterization in the treatment era

Intraoperative monitoring (IOM) using somatosensory-evoked potentials (SSEPs) plays an important role in reducing iatrogenic neurologic deficits during corrective pediatric idiopathic procedures for scoliosis. However, for unknown reasons, recent reports have cited that the sensitivity of SSEPs to detect neurologic deficits has decreased, in some to be less than 50%. This current trend, which is coincident with the addition of transcranial motor-evoked potentials, is surprising given that SSEPs are robust, reproducible responses that were previously shown to have sensitivity and specificity of >90%.Our primary aim was to assess whether SSEPs alone can detect impending neurologic deficits with similar sensitivity and specificity as originally reported. Our secondary aim was to estimate the potential predictive value of adding transcranial motor-evoked potentials to SSEP monitoring in idiopathic scoliosis procedures.This was a retrospective review to analyze the efficacy of SSEP monitoring in the group of pediatric instrumented scoliosis fusion cases.We retrospectively reviewed all consecutive cases of patients who underwent idiopathic scoliosis surgery between 1999 and 2009 at Children’s Hospital of Pittsburgh. We identified 477 patients who had the surgery with SSEP monitoring alone. Exclusion criteria included any patients with neuromuscular disorders or unreliable SSEP monitoring. Patients who had incomplete neurophysiology data or incomplete postoperative records were also excluded.Major outcomes measured were clinically significant postoperative sensory or motor deficits, as well as significant intraoperative SSEP changes.Continuous interleaved upper- and lower-extremity SSEPs were obtained throughout the duration of all procedures. We considered a persistent 50% reduction in primary somatosensory cortical amplitude or a prolongation of response latency by >10% from baseline to be significant. Persistent changes represent significant deviation in SSEP amplitude or latency in more than two consecutive averaged trials. Patients were classified into one of four categories with respect to SSEP monitoring: true positive, false positive, true negative, and false negative. The sensitivity, specificity, positive predictive value, and negative predictive value were then calculated accordingly.Our review of 477 idiopathic scoliosis surgeries monitored using SSEPs alone revealed a new deficit rate of 0.63% with no cases of permanent injury. Sensitivity = 95.0%, specificity = 99.8%, positive predictive value = 95%, negative predictive value = 99.8%. Using evidence-based epidemiologic measures, we calculated that the number needed to treat was 1,587 patients for one intervention to be performed that would have been missed by SSEP monitoring alone. In addition, the number needed to harm, which represents the increase in false positives with the addition of transcranial electrical motor-evoked potentials, was 200.SSEP monitoring alone during idiopathic scoliosis continues to be a highly reliable method for the detection and prevention of iatrogenic injury. Our results confirm the high sensitivity and specificity of SSEP monitoring alone published in earlier literature. As such, we suggest the continued use of SSEP alone in idiopathic scoliosis surgeries. At this time we do not believe there are sufficient data to support the addition of MEP monitoring, although more studies and revised criteria for the use of MEP may provide added value for its use in the future.

Prognostic value of a bilateral motor threshold criterion for facial corticobulbar MEP monitoring during cerebellopontine angle tumor resection.

In intraoperative neuromonitoring (IONM), facial nerve motor function (FaNMF) is assessed by facial muscle corticobulbar motor evoked potentials (FMcoMEP). Mostly only amplitude decrease is used as warning criterion. We related a refined criterion for FMcoMEP consisting of a bilateral final-to-baseline motor threshold ratio with standard criteria and postoperative FaNMF. 79 patients (45 females; 48 ± 16years) undergoing IONM-guided cerebellopontine angle tumor surgery were retrospectively analyzed. An intraoperative final-to-baseline motor threshold increase ≥ 20% ipsi- versus contralaterally (bFBMT20) was correlated to postoperative FaNMF at day 1 (D1), 7 (D7) and 3months (3M). An ipsilateral-only final-to-baseline motor threshold increase ≥ 20mA (iAMT20) and amplitude decrement ≥ 50% (iAR50) served as reference. Tumors included vestibular schwannomas (68%), meningiomas (19%) and others (13%). Mean tumor diameter was 2.7 ± 1.1cm. Postoperatively, HB-increase ≥ 2 was seen in 27% (D1), 17% (D7), and 6% (3M) of patients, respectively. FMcoMEP were obtained in 75/79 cases. Pathological bFBMT20, iAMT20 and iAR50 were seen in 17, 17, and 46 cases, respectively. Area under the ROC curve for bFBMT20 (iAMT20) was 0.894 (0.868) at D1; 0.903 (0.822) at D7 and 0.941 (0.959) at 3M. iAR50 performed worse at all time points. Diagnostic odds ratios were highest for bfBMT20 compared to iAMT20 and iAR50 for D1 (172.5 vs. 8.7 vs. 0.45) and D7 (51.4 vs. 6.1 vs. 0.8). The refined parameter bFBMT20 provides a valuable contribution to the prognostic assessment of FaNMF. Due to its bihemispheric character, it might thus circumvent false-positive events which affect FMcoMEP bilaterally.

Compare the Operating Condition of Two Levels of Muscle Relaxation on Facial Nerve MEP Monitoring in CPA Surgery

Compare the Operating Condition of Two Levels of Muscle Relaxation on Facial Nerve MEP Monitoring in CPA Surgery

Warning criteria for MEP monitoring during carotid endarterectomy: a retrospective study of 571 patients.

Monitoring of transcranial electrical motor evoked potentials (tcMEP) during carotid endarterectomy (CEA) has been shown to effectively detect intraoperative cerebral ischemia. The unique purpose of this study was to evaluate changes of MEP amplitude (AMP), area under the curve (AUC) and signal morphology (MOR) as additional MEP warning criteria for clamping-associated ischemia during CEA. Therefore, the primary outcome was the number of MEP alerts (AMP, AUC and MOR) in the patients without postoperative motor deficit (false positives). We retrospectively reviewed data from 571 patients who received CEA under general anesthesia. Monitoring of somatosensory evoked potentials (SSEP) and tcMEP was performed in all cases (all-or-none MEP warning criteria). The percentages of false positives (primary parameter) of AMP, AUC and MOR were evaluated according to the postoperative motor outcome. In the cohort of 562 patients, we found significant SSEP/MEP changes in 56 patients (9.96%). In 44 cases (7.83%) a shunt was inserted. Nine patients (1.57%) were excluded due to MEP recording failure. False positives were registered for AMP, AUC and MOR changes in 121 (24.01%), 148 (29.36%) and 165 (32.74%) patients, respectively. In combination of AMP/AUC and AMP/AUC/MOR false positives were found in 9.52% and 9.33% of the patients. This study is the first to evaluate the correctness of the MEP warning criteria AMP, AUC and MOR with regard to false positive monitoring results in the context of CEA. All additional MEP warning criteria investigated produced an unacceptably high number of false positives and therefore may not be useful in carotid surgery for adequate detection of clamping-associated ischemia.

Postoperative navigated transcranial magnetic stimulation to predict motor recovery after surgery of tumors in motor eloquent areas

ObjectiveTo know whether motor deficits after tumor surgery are transient is reassuring for the patient and crucial for planning rehabilitation and adjuvant treatment. We analyze the value of postoperative MRI navigated transcranial magnetic stimulation (nTMS) compared to intraoperative MEP monitoring in predicting recovery of motor function. MethodsRetrospective series of nTMS mappings within 14 days after surgery for supratentorial tumors (09/2014–05/2018). All patients with motor deficits of Medical-Research-Council-Grade (MRCS) 0–4- were included. ResultsWe performed nTMS mapping on average 3.8 days after surgery and recorded nTMS MEP in 11 of 13 patients. Motor strength recovered to at least MRCS 4 within one month if postoperative nTMS elicited MEPs (positive predictive value 90.9%). If nTMS did not elicit MEPs, the patient did not recover (negative predictive value 100%). Intraoperative MEP and postoperative nTMS were equally predictive for long-term motor recovery. In cases of intraoperative MEP alteration/signal loss, but a positive postoperative nTMS mapping, 2/3 patients demonstrated a good motor recovery. ConclusionnTMS may predict long-term motor recovery of patients suffering from severe motor deficits directly after resection of tumors located in motor eloquent areas. SignificanceIn cases of intraoperative MEP alterations, postoperative nTMS may clarify the potential for motor recovery.

Intraoperative use of transcranial motor/sensory evoked potential monitoring in the clipping of intracranial aneurysms: evaluation of false-positive and false-negative cases.

Somatosensory and motor evoked potentials (SEPs and MEPs) are often used to prevent ischemic complications during aneurysm surgeries. However, surgeons often encounter cases with suspicious false-positive and false-negative results from intraoperative evoked potential (EP) monitoring, but the incidence and possible causes for these results are not well established. The aim of this study was to investigate the efficacy and reliability of EP monitoring in the microsurgical treatment of intracranial aneurysms by evaluating false-positive and false-negative cases. From January 2012 to April 2016, 1514 patients underwent surgery for unruptured intracranial aneurysms (UIAs) with EP monitoring at the authors' institution. An EP amplitude decrease of 50% or greater compared with the baseline amplitude was defined as a significant EP change. Correlations between immediate postoperative motor weakness and EP monitoring results were retrospectively reviewed. The authors calculated the sensitivity, specificity, and positive and negative predictive values of intraoperative MEP monitoring, as well as the incidence of false-positive and false-negative results. Eighteen (1.19%) of the 1514 patients had a symptomatic infarction, and 4 (0.26%) had a symptomatic hemorrhage. A total of 15 patients showed motor weakness, with the weakness detected on the immediate postoperative motor function test in 10 of these cases. Fifteen false-positive cases (0.99%) and 8 false-negative cases (0.53%) were reported. Therefore, MEP during UIA surgery resulted in a sensitivity of 0.10, specificity of 0.94, positive predictive value of 0.01, and negative predictive value of 0.99. Intraoperative EP monitoring has high specificity and negative predictive value. Both false-positive and false-negative findings were present. However, it is likely that a more meticulously designed protocol will make EP monitoring a better surrogate indicator of possible ischemic neurological deficits.

Venous vascular malformations and compressive neuropathy

Abstract Background Venous malformations (VMs) are slow flowing congenital vascular malformations that demonstrate continuous growth. They are prone to bleeding and frequent invasion of adjacent structures. It is therefore important to differentiate them from schwannomas, which can appear similar on imaging. Currently, the literature demonstrates only a few examples of pathology misdiagnosed as a schwannoma, and of VMs associated with neurological deficits. We will illustrate the characteristics and management of VMs causing compressive neuropathy in the cervical and upper extremity regions and contrast them against the features of peripheral nerve sheath tumors. Case description Two case reports are presented, one of a 55-year-old woman with a chronic cervical mass due to a venous malformation (VM) originally misdiagnosed as a schwannoma, and another of a 35-year-old man with a vascular malformation of predominantly venous pathology in the antecubital fossa. Both patients were surgically managed. Conclusions Patients presented with chronic pain, weakness and paresthesia. Venous malformations were seen as thinly encapsulated, multilobular, heterogeneously enhancing lesions with internal fluid levels and venous lakes. Post-contrast septate enhancement, intrinsic foci of T1 hyperintensity, phleboliths, T2 hyperintensity, and nodular enhancement of torturous vessels we also noted. MEP, SSEP, and EMG monitoring was used during surgical resection. Both patients had favorable outcomes.

Friday, September 28, 2018 1:00 PM–2:30 PM abstracts: achieving lumbar interbody fusion: 199. Use of motor evoked potentials during lateral lumbar interbody fusion reduces postoperative deficits

BACKGROUND CONTEXT Intraoperative neurophysiological monitoring (IONM) has gained rather wide-spread acceptance as a method to mitigate risk to the lumbar plexus during Lateral Lumbar Interbody Fusion (LLIF) surgery. The most common approach to IONM involves using only electromyography (EMG) monitoring, and the rate of postoperative deficit remains unacceptably high. Other test modalities, such as transcranial electric motor-evoked potentials (tcMEPs) and somatosensory-evoked potentials (SSEPs), may be more suitable for monitoring neural integrity but they have not been widely adopted during LLIF. Recent studies have begun to examine their utility in monitoring LLIF surgery with favorable results. PURPOSE To evaluate the efficacy of different IONM paradigms in the prevention of iatrogenic neurologic sequelae during LLIFand to specifically evaluate the utility of including tcMEPs in an IONM strategy for LLIF surgery. STUDY DESIGN/SETTING Nonrandomized, retrospective analysis of 479 LLIF procedures at a single institution over a 4-year period. During the study epoch, three different IONM strategies were employed for LLIF procedures: (1) Surgeon-directed T-EMG monitoring (“SD-EMG”), (2) neurophysiologist-controlled T-EMG monitoring (“NC-EMG”), and (3) neurophysiologist-controlled T-EMG monitoring supplemented with MEP monitoring (“NC-MEP”). PATIENT SAMPLE The patient population was comprised of 254 males (53.5%) and 221 females (46.5%). Patient age ranged from a minimum of 21 years to a maximum of 89 years, with a mean of 56.6 years. OUTCOME MEASURES Physician-documented physiologic measures included manual muscle test (MMT) grading of hip-flexion, hip-adduction, or knee-extension, as well as hypo- or hyperesthesia of the groin and/or anterolateral thigh on the surgical side. Self-reported measures included numbness or tingling in the groin and/or anterolateral thigh on the surgical side. METHODS Patient progress notes were reviewed from the postoperative period up to 12 months after surgery. The rates of postoperative sensory and/or motor deficit consistent with lumbar plexopathy or peripheral nerve palsy on the surgical side were compared between the three cohorts. RESULTS Using the dependent measure of neurologic deficit, whether motor and/or sensory, patients with NC-MEP monitoring had the lowest rate of immediate postoperative deficit (22.3%), compared to NC-EMG monitoring (37.1%) and SD-EMG monitoring (40.4%). This result extended to sensory deficits consistent with lumbar plexopathy (pure motor deficits being excluded); patients with NC-MEP monitoring had the lowest rate (20.5%) compared to NC-EMG monitoring (34.3%) and SD-EMG monitoring (36.9%). Additionally, evaluation of postoperative motor deficits consistent with peripheral nerve palsy (pure sensory deficits being excluded), the NC-MEP group had the lowest rate (5.7%) of motor deficit compared to the SD-EMG (17.0%) and NC-EMG (17.1%) cohorts. Finally, when assessing only those patients whose last follow-up was greater than or equal to 12 months (n=251), the rate of unresolved motor deficits was significantly lower in the NC-MEP group (0.9%), as compared to NC-EMG (6.9%) and SD-EMG (11.0%). Comparison of the NC-MEP versus NC-EMG and SD-EMG groups, both independently and combined, was statistically significant (>95% confidence level) for all analyses. CONCLUSIONS The results of the present study indicate that preservation of tcMEPs from the adductor longus, quadriceps, and tibialis anterior muscles are of paramount importance for limiting iatrogenic sensory and motor injuries during LLIF surgery. In this regard, the inclusion of tcMEPs serves to compliment EMG and allows for the periodic, functional assessment of at-risk nerves during these procedures. Thus, tcMEPs appear to be the most effective modality for the prevention of both transient and permanent neurologic injury during LLIF surgery. We propose that the standard paradigm for protecting the nervous system during LLIF be adapted to include tcMEPs.

Platform Session – Evoked potentials & NIOM: Use of motor evoked potentials during lateral lumbar interbody fusion reduces postoperative deficits

Introduction Intraoperative neurophysiological monitoring (IONM) has gained rather wide-spread acceptance as a method to mitigate risk to the lumbar plexus during Lateral Lumbar Interbody Fusion (LLIF) surgery. The most common approach to IONM involves using only electromyography (EMG) monitoring, and the rate of postoperative deficit remains unacceptably high. Other test modalities, such as transcranial electric motor-evoked potentials (tcMEPs) may be more suitable for monitoring neural integrity but have not been widely adopted during LLIF. Recent studies have begun to examine their utility in monitoring LLIF surgery with favorable results. Methods We conducted a non-randomized, retrospective analysis of 479 LLIF procedures at a single institution over a four-year period. During the study epoch, three different IONM strategies were employed for LLIF procedures: (1) Surgeon-directed T-EMG monitoring (“SD-EMG”), (2) neurophysiologist-controlled T-EMG monitoring (“NC-EMG”), and (3) neurophysiologist-controlled T-EMG monitoring supplemented with MEP monitoring (“NC-MEP”). Patient progress notes were reviewed from the postoperative period up to 12 months after surgery. The rates of postoperative sensory or motor deficit consistent with lumbar plexopathy or peripheral nerve palsy on the surgical side were compared between the three cohorts. Results Using the dependent measure of neurologic deficit, whether motor and/or sensory, patients with NC-MEP monitoring had the lowest rate of immediate postoperative deficit (22.3%), compared to NC-EMG monitoring (37.1%) and SD-EMG monitoring (40.4%). This result extended to sensory deficits consistent with lumbar plexopathy (pure motor deficits being excluded); patients with NC-MEP monitoring had the lowest rate (20.5%) compared to NC-EMG monitoring (34.3%) and SD-EMG monitoring (36.9%). Additionally, evaluation of postoperative motor deficits consistent with peripheral nerve palsy (pure sensory deficits being excluded), the NC-MEP group had the lowest rate (5.7%) of motor deficit compared to the SD-EMG (17.0%) and NC-EMG (17.1%) cohorts. Finally, when assessing only those patients whose last follow-up was greater than or equal to 12 months (n = 251), the rate of unresolved motor deficits was significantly lower in the NC-MEP group (0.9%), as compared to NC-EMG (6.9%) and SD-EMG (11.0%). Comparison of the NC-MEP versus NC-EMG and SD-EMG groups, both independently and combined, was statistically significant (>95% confidence level) for all analyses. Conclusion The results of the present study indicate that preservation of tcMEPs from the adductor longus, quadriceps, and tibialis anterior muscles are of paramount importance for limiting iatrogenic sensory and motor injuries during LLIF surgery. In this regard, tcMEPs appear to be the most effective modality for the prevention of both transient and permanent neurologic injury during LLIF surgery. We propose that the standard paradigm for protecting the nervous system during LLIF be adapted to include tcMEPs.