Intra-operative monitoring of lower extremity motor-evoked potentials by direct cortical stimulation

Usefulness of Transcranial Motor Evoked Potential in Clipping Surgery for Cerebral Aneurysms-Introduction of a New Protocol for Stable Monitoring

The usefulness of transcranial motor evoked potentials (Tc-MEPs) in clipping surgery has been reported. However, numerous false positive and false negative cases were reported. We report the usefulness of a new protocol compared with direct cortical MEP (Dc-MEP).Materials were 351 patients who underwent aneurysmal clipping under simultaneous monitoring of Tc- and Dc-MEPs. A total of 337 patients without hemiparesis and 14 with hemiparesis were separately analyzed. Intraoperative changes of Tc-MEP thresholds were examined in the first 50 patients without hemiparesis. The stimulation strength of Tc-MEP was set at +20% of the stimulation threshold. As thresholds changed intraoperatively, thresholds were examined every 10 min and changed stimulation strength.Stimulation thresholds of Tc-MEP were significantly decreased after craniotomy and significantly increased after CSF aspiration. The recording ratios of Tc- and Dc-MEPs were 98.8% and 90.5%, respectively. Out of 304 patients without MEP change, 5 patients developed transient or mild hemiparesis with infarction of the territory of the perforating artery arising from the posterior communicating artery. Out of 31 patients whose MEP transiently disappeared, 3 patients developed transient or mild hemiparesis. The other two patients without MEP recovery manifested persistent hemiparesis. In 14 patients with preoperative hemiparesis, 3 patients whose healthy/affected ratio of Tc-MEP was large developed severe persistent hemiparesis.We clarified the intraoperative changes of Tc-MEP thresholds for the first time. A new protocol of Tc-MEP that followed thresholds and changed stimulation strength to +20% of thresholds is useful for stable monitoring. The usefulness of Tc-MEP is the same as that or better than that of Dc-MEP.

Motor Evoked Potential Warning Criteria in Supratentorial Surgery: A Scoping Review

During intraoperative monitoring of motor evoked potentials (MEP), heterogeneity across studies in terms of study populations, intraoperative settings, applied warning criteria, and outcome reporting exists. A scoping review of MEP warning criteria in supratentorial surgery was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sixty-eight studies fulfilled the eligibility criteria. The most commonly used alarm criteria were MEP signal loss, which was always a major warning sign, followed by amplitude reduction and threshold elevation. Irreversible MEP alterations were associated with a higher number of transient and persisting motor deficits compared with the reversible changes. In almost all studies, specificity and Negative Predictive Value (NPV) were high, while in most of them, sensitivity and Positive Predictive Value (PPV) were rather low or modest. Thus, the absence of an irreversible alteration may reassure the neurosurgeon that the patient will not suffer a motor deficit in the short-term and long-term follow-up. Further, MEPs perform well as surrogate markers, and reversible MEP deteriorations after successful intervention indicate motor function preservation postoperatively. However, in future studies, a consensus regarding the definitions of MEP alteration, critical duration of alterations, and outcome reporting should be determined.

Intraoperative Lumbar Muscle Motor Evoked Potential Monitoring With Transcortical Stimulation

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Loss of Motor Evoked Potentials Due to Carotid Artery Retraction in an Exoscopic Clipping of a Basilar Tip Aneurysm

The internal carotid artery (ICA) may inhibit visualization of a basilar tip aneurysm during an orbitozygomatic craniotomy. Retraction of the ICA may be warranted for better visualization; however, it may lead to impending neurological sequelae. Impending neurological injury due to ICA retraction may be mitigated if multi-modal neuromonitoring techniques are employed. The authors present a case report showing the contemporaneous loss of transcranial motor evoked potentials and direct cortical motor evoked potentials during an exoscopic clipping of a basilar tip aneurysm due to ICA retraction and subsequent loss of perfusion to the vascular territory supplied by ICA. The motor evoked potentials immediately returned after retraction was removed and the patient awoke neurologically intact.

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

OBJECTIVE

To 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.

METHODS

A 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.

RESULTS

Intraoperative 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.

CONCLUSIONS

Lower extremity MEPs were consistently recorded using a multi-contact cylindrical depth electrode in the interhemispheric fissure by DCS.

SIGNIFICANCE

Cylindrical depth electrodes may be a safe and effective alternative for DCS in the interhemispheric fissure, where subdural strips are difficult to place.

Intraoperative evoked potential monitoring for detecting cerebral injury during adult aneurysm clipping surgery: a systematic review and meta-analysis of diagnostic test accuracy

OBJECTIVES

We aim to evaluate the diagnostic test accuracy (DTA) of intraoperative evoked potential (EP) monitoring to detect cerebral injury during clipping of cerebral aneurysms.

DESIGN

Systematic review.

DATA SOURCES

Major electronic databases including MEDLINE, EMBASE, LILACS.

ELIGIBILITY CRITERIA

We included studies that reported the DTA of intraoperative EP monitoring during intracranial aneurysm clipping procedures in adult patients.

DATA EXTRACTION AND SYNTHESIS

After quality assessment, we performed a meta-analysis using the bivariate random effects model, and calculated the possible range of DTA point estimates using a new best-case/worst-case scenario approach to quantify the impact of rescue intervention on DTA.

RESULTS

A total of 35 studies involving 4011 patients were included. The quality of the primary studies was modest and the heterogeneity across studies was high. The pooled sensitivity and specificity for predicting postoperative neurological deficits for the somatosensory evoked potential (SSEP) monitoring was 59% (95% CI: 39% to 76%; I²: 76%) and 86% (95% CI: 77% to 92%; I²: 94%), for motor evoked potential (MEP) monitoring was 81% (95% CI: 58% to 93%; I²: 54%) and 90% (95% CI: 86% to 93%; I²: 81%), and for combined SSEP and MEP monitoring was 92% (95% CI: 62% to 100%) and 88% (95% CI: 83% to 93%). The best-case/worst-case range for the pooled point estimates for sensitivity and specificity for SSEP was 50%-63% and 81%-100%, and for MEP was 59%-74% and 93%-100%, and for combined SSEP and MEP was 89%-94% and 83%-100%.

CONCLUSIONS

Due to the modest quality and high heterogeneity of the existing primary studies, it is not possible to confidently support or refute the diagnostic value of EP monitoring in cerebral aneurysm clipping surgery. However, combined SSEP and MEP appears to provide the best DTA for predicting postoperative stroke. Contrary to popular assertion, the modest sensitivity of SSEP monitoring is not explained by the use of rescue intervention.

PROSPERO REGISTRATION NUMBER

CRD42015016884.

Intraoperative Neurophysiologic Monitoring for Degenerative Cervical Myelopathy

Multimodal intraoperative neurophysiologic monitoring is a reliable tool for detecting intraoperative spine injury and is recommended during surgery for degenerative cervical myopathy (DCM). Somatosensory evoked potential (SEP) can be used to monitor spine and peripheral nerve injury during positioning in surgery for DCM. Compensation technique for transcranial evoked muscle action potentials (tcMEPs) should be adopted in intraoperative monitoring during surgery for DCM. Free-running electromyography is a useful real-time monitoring add-on modality in addition to SEP and tcMEP.

The Diagnostic Accuracy of Evoked Potential Monitoring Techniques During Intracranial Aneurysm Surgery for Predicting Postoperative Ischemic Damage: A Systematic Review and Meta-Analysis

OBJECTIVE

To investigate the diagnostic accuracy of various evoked potential monitoring techniques in predicting postoperative neurologic deficit in intracranial aneurysm surgery.

METHODS

A literature search of the MEDLINE, Embase, and Cochrane databases was conducted for English language articles published between March 31, 1983 and March 31, 2016. Original studies that reported the use of evoked potential monitoring during intracranial aneurysm surgery in predicting postoperative neurologic damage were selected, and their relevant reference lists were hand searched. Test performance characteristics were summarized using hierarchic summary receiver operating characteristic (ROC) curves and bivariable random-effects models.

RESULTS

Thirteen qualifying studies (1597 patients; 1689 aneurysms) from 6 countries were identified. Eight studies investigated the use of the somatosensory evoked potential (SSEP) monitoring technique, 5 investigated transcranial motor evoked potential (TcMEP) and another 5 investigated direct cortical motor evoked potential (DMEP). Bivariable pooled sensitivity and specificity were 48% (95% confidence interval [CI], 30.7-65.0) and 92% (CI, 88%-94.4%), respectively, for SSEP; 73% (CI, 21.0%-96.7%) and 94% (CI, 87.1%-97.5%) for TcMEP; and 97% (CI, 74.43%-99.99%) and 89% (CI, 84.0%-94.5%) for DMEP. ROC curve analysis showed that TcMEP had the highest accuracy (area under ROC curve 0.95; 95% CI, 0.93-0.97), followed by DMEP (0.91, 0.89-0.94) and SSEP (0.88, 0.85-0.91).

CONCLUSIONS

TcMEP and DMEP have higher diagnostic accuracy than SSEP in predicting postoperative neurologic deficit. The type of anesthetic agent, the use of neuromuscular blocking drugs, and the choice of diagnostic criteria for significant change in cerebral blood flow during aneurysm surgery affect the diagnostic accuracy of evoked potential techniques in predicting postoperative neurologic deficit.

Effects of transcranial stimulating electrode montages over the head for lower-extremity transcranial motor evoked potential monitoring

OBJECTIVE The aim of this study was to determine the most effective electrode montage to elicit lower-extremity transcranial motor evoked potentials (LE-tMEPs) using a minimum stimulation current. METHODS A realistic 3D head model was created from T1-weighted images. Finite element methods were used to visualize the electric field in the brain, which was generated by transcranial electrical stimulation via 4 electrode montage models. The stimulation threshold level of LE-tMEPs in 52 patients was also studied in a practical clinical setting to determine the effects of each electrode montage. RESULTS The electric field in the brain radially diffused from the brain surface at a maximum just below the electrodes in the finite element models. The Cz-inion electrode montage generated a centrally distributed high electric field with a current direction longitudinal and parallel to most of the pyramidal tract fibers of the lower extremity. These features seemed to be effective in igniting LE-tMEPs. Threshold level recordings of LE-tMEPs revealed that the Cz-inion electrode montage had a lower threshold on average than the C3-C4 montage, 76.5 ± 20.6 mA and 86.2 ± 20.6 mA, respectively (31 patients, t = 4.045, p < 0.001, paired t-test). In 23 (74.2%) of 31 cases, the Cz-inion montage could elicit LE-tMEPs at a lower threshold than C3-C4. CONCLUSIONS The C3-C4 and C1-C2 electrode montages are the standard for tMEP monitoring in neurosurgery, but the Cz-inion montage showed lower thresholds for the generation of LE-tMEPs. The Cz-inion electrode montage should be a good alternative for LE-tMEP monitoring when the C3-C4 has trouble igniting LE-tMEPs.

Strategies and Pitfalls of Motor-Evoked Potential Monitoring during Supratentorial Aneurysm Surgery

BACKGROUND

The aims of this study were to reveal the strategies and pitfalls of motor-evoked potential (MEP) monitoring methods during supratentorial aneurysm surgery, and to discuss the drawbacks and advantages of each method by reviewing our experiences.

METHODS

Intraoperative MEP monitoring was performed in 250 patients. Results from 4 monitoring techniques using combinations of 2 stimulation sites and 2 recording sites were analyzed retrospectively.

RESULTS

MEP was recorded successfully in 243 patients (97.2%). Direct cortical stimulation (DCS)-spinal recorded MEP (sMEP) was used in 134 patients, DCS-muscle recorded MEP (mMEP) in 97, transcranial electrical stimulation (TES)-mMEP in 11 and TES-sMEP in 1. TES-mMEP during closure of the skull was used in 21 patients. DCS-mMEP was able to detect waveforms from upper and/or lower limb muscles. Alternatively, DCS-sMEP (direct [D]-wave) could accurately estimate amplitude changes. A novel "early warning sign" indicating ischemia was found in 21 patients, which started with a transiently increased amplitude of D-wave and then decreased after proximal interruption of major arteries. False-negative findings in MEP monitoring in 2 patients were caused by a blood insufficiency in the lenticulostriate artery and by a TES-sMEP recording, respectively.

CONCLUSIONS

The results of this study suggest that to perform accurate MEP monitoring, DCS-mMEP or DCS-sMEP recording should be used as the situation demands, with combined use of TES-mMEP recording during closure of the skull. DCS-sMEP is recommended for accurate analysis of waveforms. We also propose a novel "early warning sign" of blood insufficiency in the D-wave.

Motor evoked potential monitoring during surgery of middle cerebral artery aneurysms: a cohort study

BACKGROUND

Motor evoked potential (MEP) monitoring has been widely used in brain or spine surgery to recognize potential damage of the pyramidal motor system. However, its ability to detect ischemic injury during middle cerebral artery (MCA) aneurysm surgery remains unclear. A prospective cohort study was designed to evaluate MEP changes during MCA aneurysm surgery.

METHODS

From January 2009 to August 2011, 89 patients underwent MCA aneurysm surgery and were prospectively divided into 2 groups: MEP monitoring group and control group. Based on an amplitude decrement of >50% or loss, a 2-stage warning criterion of MEP changes was established. Concomitant somatosensory evoked potential changes were also recorded. MEP changes occurred in 15 patients, and various methods were used to avoid continued brain ischemia. Indocyanine green angiography and Doppler ultrasonography were performed if needed. A head computed tomography scan was performed immediately and the day after the operation.

RESULTS

At discharge, neither motor status nor Glasgow Coma Scale score was significantly different between the 2 groups. However, at the latest follow-up (mean, 31.9 months), motor status of the patients in the monitoring group was better (P = 0.037). MEP monitoring was identified as an independent prognostic factor for motor outcome in long-term results by multivariate analysis (P = 0.042). Both wave loss and >50% amplitude decrement of MEP monitoring showed good predictive value when used as part of a 2-stage warning criterion.

CONCLUSIONS

MEP monitoring is reliable for evaluation of the ischemic status of the pyramidal motor system during MCA aneurysm surgery and can improve surgical outcomes when used appropriately.

The significance of intraoperative monitoring of muscle motor evoked potentials during unruptured large and giant cerebral aneurysm surgery

The goal of this study was to characterize the utility of muscle motor evoked potentials (MMEPs) elicited by direct cortical stimulation as a means of monitoring during unruptured large and giant cerebral aneurysm surgery. This analysis focused on intraoperative changes in MMEPs and their relationship to postoperative motor function. The study population consisted of 50 patients who underwent surgery for large (n = 31) or giant (n = 19) cerebral aneurysms. Intraoperative MMEPs were continuously and successfully obtained in muscles belonging to the vascular territory of interest. There was no postoperative motor paresis in 31 (62%) patients in whom intraoperative MMEPs remained unchanged. Transient MMEP change occurred in 15 (30%) of the 50 patients, but 9 of those patients had no postoperative motor deficits, 5 had transient motor deficits, and 1 suffered permanent motor deficits resulting from postoperative delayed blood flow insufficiency due to arteriosclerosis of the parent artery. Permanent MMEP loss occurred in 4 (8%) of 50 patients, all of whom developed severe and permanent postoperative motor deficits. MMEP is a useful monitoring modality in patients undergoing surgery for large or giant cerebral aneurysms. This strategy can help predict functional prognosis or guide the neurosurgeon intraoperatively in an effort to promote better outcomes.

A case of thrombosed giant aneurysm of the azygos anterior cerebral artery: clipping under monitoring of motor evoked potentials of the lower extremities

Giant aneurysms of the distal anterior cerebral artery (ACA), especially the azygos ACA, are rare. We treated a patient with giant aneurysm of the azygos ACA who underwent aspiration of thrombus and clipping under monitoring of motor evoked potentials of the lower extremities (L-MEPs), resulting in remarkable recovery of motor and intellectual function. A 72-year-old male was admitted with left motor weakness persisting for 2 weeks. Neurologically, disorientation and intellectual impairment were also noted. Imaging disclosed a 60-mm diameter aneurysm with heterochronous thrombi arising from the distal bifurcation of the azygos ACA. One month after the onset, radical surgery was scheduled. The azygos ACA was secured and the aneurysm was dissected, and the distal parts of the azygos ACA were confirmed. After removal of the thrombus, the neck was reconstructed with eight clips. L-MEPs disappeared due to occlusion of the azygos ACA for 20 minutes but reappeared after 22 minutes and normalized 78 minutes after reperfusion. Motor weakness improved entirely with mini-mental state examination score of 29 points at 1 month after surgery. One year later, Wechsler Adult Intelligence Scale-Third Edition and Wechsler Memory Scale-Revised scores reached normal levels. Review of reported cases found this aneurysm tends to occur in males in their 50s to 70s presenting with mass sign. Decompression of the aneurysm in the frontal lobe and monitoring of L-MEPs during temporary occlusion of the ACA are important.