Continuous Motor Evoked Potentials Monitoring Research Articles

Importance of Multimodal Spinal Cord Monitoring and Hemodynamic Augmentation during High Thoracic Ventral Dural Tear Repair Using the Posterior Approach

AbstractCerebrospinal fluid (CSF) leakage due to large ventral dural tears (VDT) often requires surgical intervention. Surgical closure of a high thoracic VDT is challenging and associated with high morbidity, especially if it is performed after multiple epidural blood patch (EBP)/fibrin glue injections. A 44-year-old woman was diagnosed with spontaneous intracranial hypotension due to VDT at T1-T2, causing CSF leakage. Multiple EBP and fibrin glue injections failed to treat her symptoms; hence, the patient underwent surgical closure using the posterior approach. The patient was anesthetized using standard anesthetic drugs and was maintained under total intravenous anesthesia to facilitate continuous motor-evoked potential (MEP) monitoring. The surgical course was complicated by bleeding, hypotension, and MEP loss. Continuous MEP monitoring, effective team communication, quick restoration of blood pressure(BP) and BP augmentation with fluid, blood, and vasopressor helped to restore the MEP back to baseline. Hence, the patient recovered without neurological morbidity. This case report highlights the importance of adequate vascular access, multimodal spinal cord monitoring, and BP augmentation during a high thoracic VDT repair.

Gross Total Resection of a Grade IV Astrocytoma Adjacent to the Precentral Gyrus With Nonawake Motor Mapping and Motor-Evoked Potential Monitoring: 3-Dimensional Operative Video.

Surgical treatment of the gliomas located in or adjacent to the eloquent areas poses significant challenge to neurosurgeons. The main goal of the surgery is to achieve maximal safe resection while preserving the neurological function. This might be possible with utilizing pre- and intraoperative adjuncts such as functional magnetic resonance imaging (MRI), image guidance, mapping of the function of interest, intraoperative MRI, and neurophysiological monitoring. In this video, we demonstrate the utilization of nonawake mapping and motor-evoked potential (MEP) monitoring for the resection of a right-sided posterior superior frontal gyrus grade IV astrocytoma adjacent to the primary motor cortex. The patient is a 69-yr-old woman presented with multiple episodes of simple partial seizures involving her left leg and spreading to the left arm. MRI and functional MRI examinations showed a heterogeneously enhancing mass with peritumoral edema adjacent to the primary motor cortex. Because the patient did not want to undergo an awake craniotomy, a decision was made to perform the resection of the tumor with nonawake motor mapping and continuous MEP monitoring. Nonawake motor mapping and MEP monitoring enabled us to perform gross total resection. Because it has been shown that supratotal resection may provide improved survival outcome,1,2 we extended the white matter resection beyond the contrast enhancing area in noneloquent parts of the tumor. Surgical steps in dealing with vascular anatomy as well as utilizing intraoperative adjuncts such as motor mapping and MEP monitoring to enhance the extent of resection while preserving the function are demonstrated in this 3-dimensional surgical video. The patient consented to publication of her operative video.

Intraoperative subcortical motor evoked potential stimulation: how close is the corticospinal tract?

Subcortical stimulation is a method used to evaluate the distance from the stimulation site to the corticospinal tract (CST) and to decide whether the resection of an adjacent lesion should be terminated to prevent damage to the CST. However, the correlation between stimulation intensity and distance to the CST has not yet been clearly assessed. The objective of this study was to investigate the appropriate correlation between the subcortical stimulation pattern and the distance to the CST. Monopolar subcortical motor evoked potential (MEP) mapping was performed in addition to continuous MEP monitoring in 37 consecutive patients with lesions located in motor-eloquent locations. The proximity of the resection cavity to the CST was identified by subcortical MEP mapping. At the end of resection, the point at which an MEP response was still measurable with minimal subcortical MEP intensity was marked with a titanium clip. At this location, different stimulation paradigms were executed with cathodal or anodal stimulation at 0.3-, 0.5-, and 0.7-msec pulse durations. Postoperatively, the distance between the CST as defined by postoperative diffusion tensor imaging fiber tracking and the titanium clip was measured. The correlation between this distance and the subcortical MEP electrical charge was calculated. Subcortical MEP mapping was successful in all patients. There were no new permanent motor deficits. Transient new postoperative motor deficits were observed in 14% (5/36) of cases. Gross-total resection was achieved in 75% (27/36) and subtotal resection (> 80% of tumor mass) in 25% (9/36) of cases. Stimulation intensity with various pulse durations as well as current intensity was plotted against the measured distance between the CST and the titanium clip on postoperative MRI using diffusion-weighted imaging fiberitracking tractography. Correlational and regression analyses showed a nonlinear correlation between stimulation intensity and the distance to the CST. Cathodal stimulation appeared better suited for subcortical stimulation. Subcortical MEP mapping is an excellent intraoperative method to determine the distance to the CST during resection of motor-eloquent lesions and is highly capable of further reducing the risk of a new neurological deficit.

Low-threshold monopolar motor mapping for resection of lesions in motor eloquent areas in children and adolescents

Resection of lesions close to the primary motor cortex (M1) and the corticospinal tract (CST) is generally regarded as high-risk surgery due to reported rates of postoperative severe deficits of up to 50%. The authors' objective was to determine the feasibility and safety of low-threshold motor mapping and its efficacy for increasing the extent of lesion resection in the proximity of M1 and the CST in children and adolescents. The authors analyzed 8 consecutive pediatric patients in whom they performed 9 resections for lesions within or close (≤ 10 mm) to M1 and/or the CST. Monopolar high-frequency motor mapping with train-of-five stimuli (pulse duration 500 μsec, interstimulus interval 4.0 msec, frequency 250 Hz) was used. The motor threshold was defined as the minimal stimulation intensity that elicited motor evoked potentials (MEPs) from target muscles (amplitude > 30 μV). Resection was performed toward M1 and the CST at sites negative to 1- to 3-mA high-frequency train-of-five stimulation. The M1 was identified through high-frequency train-of-five via application of varying low intensities. The lowest motor thresholds after final resection ranged from 1 to 9 mA in 8 cases and up to 18 mA in 1 case, indicating proximity to motor neurons. Intraoperative electroencephalography documented an absence of seizures during all surgeries. Two transient neurological deficits were observed, but there were no permanent deficits. Postoperative imaging revealed complete resection in 8 patients and a very small remnant (< 0.175 cm3) in 1 patient. High-frequency train-of-five with a minimal threshold of 1-3 mA is a feasible and safe procedure for resections in the proximity of the CST. Thus, low-threshold motor mapping might help to expand the area for safe resection in pediatric patients with lesions located within the precentral gyrus and close to the CST, and may be regarded as a functional navigational tool. The additional use of continuous MEP monitoring serves as a safety feedback for the functional integrity of the CST, especially because the true excitability threshold in children is unknown.

82. Motor evoked potentials are very sensitive to blood pressure in insular glioma surgery: A case report

Since many years Motor Evoked potentials (MEPs) have been considered as a valuable tool to assess the integrity of motor pathways (Deletis, 1993). In brain tumor surgery, MEP are of particular value during the removal of insular glioma where the mechanism of injury is mainly vascular (Neuloh et al., 2007). We present and discuss the case of an insular glioma where MEP were lost during continuous monitoring through Direct Cortical Stimulation (DCS). A 47 year old female was operated on a left insular glioma. After the central sulcus was identified through the phase reversal technique, we performed continuous MEP monitoring (train of 4, ISI 2.5 ms, baseline intensity of stimulation 20 mA) from contra lateral upper and lower extremity muscles, through a 8 channels strip electrode placed over the motor cortex. A sudden disappearance of all MEPs occurred during tumor resection. Before MEPs loss, blood pressure dropped from 120 to 88 mm Hg. At this point stimulation intensity was increased up to 30 mA without any recovery of MEPs. To follow, papaverine was locally instilled to counteract vasospastic changes but this also carried no effect on MEPs. Finally, blood pressure progressively recovered to 110 mmHg and only at that time MEPs started to recover at 20 mA of stimulation intensity. At closing, MEPs completely recovered to baseline. Post-operative outcome was negative for motor impairment. Muscle MEPs are very sensitive to subcortical ischemia. Among corrective measures, to increase blood pressure proved to be more effective than papaverine and increased stimulation intensity to facilitate MEP recovery.

Quantitative Subcortical Motor Mapping and Continuous Motor-Evoked Potential Monitoring during Surgery of Supratentorial Brain Tumors

Aim: Mapping and monitoring are increasingly used during the resection of tumors located close to the corticospinal tract (CST). The objective was to compare lowest subcortical stimulation thresholds (MT) and motor-evoked potential (MEP) monitoring signal abnormalities in correlation to motor function outcome.

Predictive Value and Safety of Intraoperative Neurophysiological Monitoring With Motor Evoked Potentials in Glioma Surgery

Resection of gliomas in or adjacent to the motor system is widely performed with intraoperative neuromonitoring (IOM). Despite the fact that data on the safety of IOM are available, the significance and predictive value of the procedure are still under discussion. Moreover, cases of false-negative monitoring affect the surgeon's confidence in IOM. To examine cases of false-negative IOM to reveal structural explanations. Between 2007 and 2010, we resected 115 consecutive supratentorial gliomas in or close to eloquent motor areas using direct cortical stimulation for monitoring of motor evoked potentials (MEPs). The monitoring data were reviewed and related to new postoperative motor deficit and postoperative imaging. Clinical outcomes were assessed during follow-up. Monitoring of MEPs was successful in 112 cases (97.4%). Postoperatively, 30.3% of patients had a new motor deficit, which remained permanent in 12.5%. Progression-free follow-up was 9.7 months (range, 2 weeks-40.6 months). In 65.2% of all cases, MEPs were stable throughout the operation, but 8.9% showed a new temporary motor deficit, whereas 4.5% (5 patients) presented with permanently deteriorated motor function representing false-negative monitoring at first glance. However, these cases were caused by secondary hemorrhage, ischemia, or resection of the supplementary motor area. Continuous MEP monitoring provides reliable monitoring of the motor system, influences the course of operation in some cases, and has to be regarded as the standard for IOM of the motor system. In our series, we found no false-negative MEP results.

Continuous motor monitoring enhances functional preservation and seizure-free outcome in surgery for intractable focal epilepsy

Complete yet safe resection close to motor areas in medically intractable epilepsy requires functional information. New deficit may occur despite preservation of motor cortex, e.g., through vascular compromise. Here, we explore for the first time the feasibility, safety, and the clinical value of continuous motor-evoked potential (MEP) monitoring in focal epilepsy surgery. High-frequency stimulation for MEP monitoring was performed during 100 consecutive lesionectomies critically related to motor areas and pathways. Extraoperative motor cortex mapping was performed in 27 of these cases via chronically implanted subdural grid electrodes. MEP monitoring results, postoperative motor outcome, and seizure control were correlated in a prospective observational design. Reliable MEP monitoring was achieved in 86 cases. Young age was the only discernible cause of unsuccessful recordings. Seizures from cortex stimulation did not occur. MEP changes (36%) predicted new motor deficit (17%) in all cases except purely cortical lesions. MEP changes predicted occurrence and permanence of new pareses. New deficit was significantly more frequent without (as compared with) successful monitoring (43% vs. 17%); permanently severe pareses from ischemia occurred only without MEPs (21% vs. 0%). Complete seizure control was significantly more frequent in successfully monitored cases (60% vs. 31%). Even with extraoperative motor mapping, severe paresis occurred only among cases with unsuccessful MEPs. Continuous MEP monitoring in epilepsy surgery is feasible and safe. It reflects motor function complementarily to the localizing motor mapping results. Successful MEP monitoring correlates with unimpaired motor outcome and full seizure control.