Transcranial Electrical Stimulation Of Motor Cortex Research Articles

The role of facial nerve motor evoked potentials in predicting facial nerve function in vestibular schwannoma surgery

Objective: To analyze the role of facial nerve motor evoked potentials in predicting facial nerve function in vestibular schwannoma surgery. Methods: In a retrospective clinical study of 226 patients with acoustic neuroma, admitted to our hospital from January 2016 to May 2019, were investigated by facial nerve motor evoked potentials (FNMEP) elicited by multi-pulse transcranial electrical motor cortex stimulation from. For recording the same electrode set-up was used as for continuous EMG monitoring of the orbicularis oculi,oris muscles and mentalis. Pre-surgical (opening dural), intraoperative and post-surgical (closing dural) FNMEP amplitudes and latencies were recorded. End (closing dura) to start (opening dura) amplitude ratios were compared to early-term(3 day after surgery) facial nerve function by House-Brackmann(HB) Grading. Results: 201 patients(88.9%) get a total tumor resection, 15 patients (6.6%) were a subtotal resection, 10 patients(4.4%) were a partial resection. 100 percent of patients had a integrated anatomical preservation of facial nerves, there were four (1.8%) death cases in this group. Reliable FNMEPs were obtained in all patients. The ratio of end-operative to start-operative FNMEP-amplitude showed a negative correlation with early facial nerve function. Correlation was especially close with early function: an amplitude preservation rate of 85.3% led to HB Ⅰ or Ⅱ in 190(84.1%) patients, of 45.6% to HB Ⅲ in 17(7.5%) patients, of 23.1% to HB Ⅳ in 13(5.8%) patients and of 6.7% to HB Ⅴor Ⅵ in 6(2.7%) patients. There was a negative correlation between FNMEP amplitude ratio and post-surgical early HB grading(r=-0.895, P=0.000). Conclusion: FNMEP was highly reliable in predicting early postoperative facial function of the resection of vestibular schwannoma, was a valid protection technique of facial nerve.

Application of transcranial electrical stimulation-facial nerve motor evoked potentials in resection of large acoustic neuromas

Objective To discuss the role of transcranial electrical stimulation facial nerve motor evoked potentials (TCE-FNMEP) in resection of large acoustic neuromas. Methods In a retrospective clinical study, 58 patients with large acoustic neuroma were investigated at Department of Neurosurgery, Tianjin HuanHu Hospital form July 2016 to March 2017.All patients were investigated by facial nerve motor evoked potentials elicited by multi-pulse transcranial electrical motor cortex stimulation. For recording, the same electrode set-up was used as for continuous EMG (electromyogram) monitoring of the orbicularis oculi, oris muscles and mentalis. Pre-surgical (dura opening), intraoperative and post-surgical (dura closing) TCE-FNMEP amplitudes and latencies were documented. End (dura closing) to start (dura opening) amplitude ratios were compared to early-term (1 day post surgery) facial nerve function by House-Brackmann (H-B) grading. Results Fifty-one (87.9%, 51/58) patients obtained total tumor resection and 7 (12.1%, 7/58) achieved subtotal resection. All patients had anatomical preservation of facial nerves. There was no death in this series. Reliable TCE-FNMEPs were obtained in all patients. At 1 day post operation, 48 out of 58 case were graded as H-B Ⅰ-Ⅱ, the range of TCE-FNMEP amplitude ratio was 47.6%-100.0%, and the median was 85.4%. Five cases were graded as H-B Ⅲ, the range of TCE-FNMEP amplitude ratio was 43.2%-55.8%, and the median was 45.4%. Three cases were graded as H-B Ⅳ, the range of TCE-FNMEP amplitude ratio was 31.4%-53.2%, and the median was 33.6%. Two cases were graded as H-B Ⅴ-Ⅵ, the range of TCE-FNMEP amplitude ratio was 6.1% and 11.3%, respectively. There was a negative correlation between TCE-FNMEP amplitude ratio and early post-surgical HB grading (r=-0.611, P<0.01). Conclusion TCE-FNMEP seems to be highly reliable in predicting early postoperative facial function in resection of large acoustic neuromas and could be a valid protection technique of facial nerve. Key words: Neuroma, acoustic; Facial nerve; Evoked potentials, motor; Transcranial electrical stimulation

Facial motor evoked potentials in cerebellopontine angle surgery: Technique, pitfalls and predictive value

Objective To obtain information on functional integrity of the facial nerve by transcranial electrical motor evoked potentials independent of nerve visualization and to improve prediction of postoperative function. Patients and methods In a prospective clinical study, 68 patients with cerebello-pontine angle tumors and 5 patients with trigeminal neuralgia were investigated by facial motor evoked potentials (FMEP) elicited by multi-pulse transcranial electrical motor cortex stimulation. For recording the same electrode set-up was used as for continuous EMG monitoring of the orbicularis oculi and oris muscles. Pre-surgical FMEP amplitudes and latencies were correlated with tumor extensions. End to start amplitude ratios were compared to early and long-term facial nerve function by House–Brackmann-Grading (HB) documented by pre- and post-operative photo and video documentation. Results Reliable FMEP were obtained in 57 patients. FMEP responses at the start of surgery correlated with the degree of tumor extension. Largest FMEP amplitudes and shortest latencies were found in patients with trigeminal neuralgia. FMEP quality was reduced with increasing tumor extension ( P < 0.05). The ratio of end-operative to start-operative FMEP-amplitude showed a positive correlation with early and late facial nerve function. Correlation was especially close with early function: an amplitude preservation rate of 86% led to HB°1 or HB°2, of 67% to HB°3, at 33% to HB°4 and at 15% or lower to HB°5 or HB°6. Discussion Initial FMEP amplitudes correlate with the presumed pre-operative nerve affection by space occupying tumors, a phenomenon reported here for the first time. Intact FMEP are highly reliable for preserved nerve continuity and hereby are of special help to the neurosurgeon for those surgical phases where the facial nerve is not visible and still covered by tumor and where conventional EMG monitoring is of very limited use. The end-to-start amplitude ratio of the FMEP is closely related to early and late clinical function. Amplitude reduction by 30% or more should result in a change of microsurgical action to enable fast recovery. Conclusion As an adjunct to intraoperative EMG, FMEP are superior in two respects, first in identifying pre-surgical latent nerve lesions and second in monitoring nerve integrity without direct nerve visualization. FMEP are highly reliable in predicting early and late postoperative function.

Intraoperative neurophysiologic monitoring for intramedullary spinal-cord tumor surgery

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

Intraoperative neurophysiologic monitoring for intramedullary spinal cord tumor surgery

Intraoperative neurophysiological monitoring is an integral part of surgery for intramedullary spinal cord tumors. Motor evoked potentials are the key technology for this purpose. Sensory evoked potentials play a limited role. Motor potentials are evoked by transcranial electrical motor cortex stimulation. The single-stimulus technique elicits D-waves, which are recorded from the spinal cord. The multipulse technique elicits muscle MEPs, which are recorded from limb muscles. The amplitude of the D-waves and the presence or absence of muscle MEPs are the critical parameters for MEP interpretation. The practical procedures for evoked potential recording are well suited to a neurosurgical environment, and the intraoperative interpretation and application of neurophysiological information is fast and straightforward, particularly for MEPs. MEPs can almost always be recorded in a patient who is not already severely disabled before surgery. Pre- and postoperative clinical motor findings correlate with the intraoperative MEP findings. As a result a patient's clinical status can be predicted any time during the operation with considerable certainty (the sensitivity of muscle MEPs for post-operative motor deficits is almost 100%; its specificity is about 90%). Therefore, MEP data reflect the clinical “reality” in an individual patient. Loss of muscle MEPs, interpreted in combination with an incremental decrease in the amplitude of the D-wave, provides a “window of warning.” It reflects a pattern of MEP change consistent with a reversible injury to the essential motor pathways. The surgical strategy can be adapted before irreversible neurological damage occurs. Present and stable recordings allow complete resection of tumors with confidence about the integrity of the motor pathways.

Motor-evoked potential monitoring for intramedullary spinal cord tumor surgery: correlation of clinical and neurophysiological data in a series of 100 consecutive procedures

Resection of intramedullary spinal cord tumors carries a high risk for surgical damage to the motor pathways. This surgery is therefore optimal for testing the performance of intraoperative motor evoked potential (MEP) monitoring. This report attempts to provide evidence for the accurate representation of patients' pre- and postoperative motor status by combined epidural and muscle MEP monitoring during intramedullary surgery. The authors used transcranial electrical motor cortex stimulation to elicit MEPs, which were recorded from the spinal cord (with an epidural electrode) and from limb target muscles (thenar, anterior tibial) with needle electrodes. The amplitude of the epidural MEPs and the presence or absence of muscle MEPs were the parameters for MEP interpretation. A retrospective analysis was performed on data from the resection of 100 consecutive intramedullary tumors and MEP data were compared with the pre- and postoperative motor status. Intraoperative monitoring was feasible in all patients without severe preoperative motor deficits. Preoperatively paraplegic patients had no recordable MEPs. The sensitivity of muscle MEPs to detect postoperative motor deficits was 100% and its specificity was 91%. There was no instance in which a patient with stable MEPs developed a motor deficit postoperatively. Intraoperative MEPs adequately represented the motor status of patients undergoing surgery for intramedullary tumors. Because deterioration of the motor status was transient in all cases, it can be considered that impairment of the functional integrity of the motor pathways was detected before permanent deficits occurred.