Multimodal intraoperative monitoring: an overview and proposal of methodology based on 1,017 cases

A multichannel electromyography dataset for continuous intraoperative neurophysiological monitoring of cranial nerve

Continuous Intraoperative Neurophysiologic Monitoring (cIONM) is a widely used technology to improve surgical outcomes and prevent cranial nerve injury during skull base surgery. Monitoring of free-running electromyogram (EMG) plays an important role in cIONM, which can be used to identify different discharge patterns, alert the surgeon to potential nerve damage promptly, etc. In this dataset, we collected clinical multichannel EMG signals from 11 independent patients' data using a Neuromaster G1 MEE-2000 system (Nihon Kohden, Inc., Tokyo, Japan). Through innovative classification methods, these signals were categorized into seven different categories. Remarkably, channel 1 and channel 2 captured continuous EMG signals from the facial nerve (VII cranial nerve), while channel 3 to channel 6 focused on V, XI, X, and XII cranial nerves. This is the first time that intraoperative EMG signals have been collated and presented as a dataset and labelled by professional neurophysiologists. These data can be utilized to develop the architecture of neural networks in deep learning, machine learning, pattern recognition, and other commonly employed biomedical engineering research methods, thereby providing valuable information to enhance the safety and efficacy of surgical procedures.

Multimodal Intraoperative Neurophysiological Monitoring in Cranial and Spinal Tumour Surgeries: A Descriptive Observational Study

Intraoperative neurophysiological monitoring (IONM) involves monitoring the functional integrity of critical brain regions and pathways as well as identifying and preserving functionally viable neural tissues (mapping) during surgery using electrophysiological techniques. Multimodality combines various neurophysiological techniques to optimise diagnostic effectiveness and to improve the outcomes of the surgeries. The present study is a case series with comprehensive and illustrative descriptions of the neurophysiological changes in five neuromonitored cases of cranial and spinal cord tumour surgeries conducted with a multimodal approach. The cases were monitored with somatosensory evoked potentials (SSEP), transcranial motor evoked potentials (TcMEP), and both free run and triggered electromyography (fEMG and tEMG). No false negative outcomes were identified in the cases studied as there was an association of absence of change in SSEP and TcMEP both, with no neurological deficit postoperatively. Two cases were identified as having true positive neuromonitoring alerts. No false positive alerts were found in any case. Multimodal monitoring using SSEP, TcMEP, and EMG (fEMG and tEMG) in cranial and spinal tumour surgeries can improve performance with fewer false-negative and false-positive results. Neuromonitoring approaches used in combination can provide reliable information regarding postoperative neurological outcomes.

Factors Related to the Deterioration of Postoperative Lower Back Pain in Hemilaminectomy Approach for Lumbar Spinal Schwannoma Resection

Objective

This study aimed to explore the related risk factors in patients who underwent hemilaminectomy for lumbar spinal schwannoma resection and who experienced deterioration of postoperative lower back pain in comparison to preoperative pain levels.

Methods

This retrospective study recruited 61 patients from the First Affiliated Hospital of An Hui Medical University between January 2018 and June 2019. All data were collected from clinical records and analyzed at 1-month and at 1-year follow-up. The visual analog scale (VAS) was used to evaluate pain, and neurologic function was assessed using the Modified McCormick Scale. Intraoperative neurophysiological monitoring was used to assess neuronal integrity and mitigate injury. Statistical analysis of the data was performed using the SPSS version 19 software.

Results

Preoperative pain improved dramatically in the 1-year follow-up (VAS: preoperative, 3.84±2.19; 1-year follow-up, 2.13±2.26; P<0.001). The pain-improved group and worsened group showed a significant difference at 1-month (VAS: 1.76±1.56; 5.54±1.26; P<0.05) and at 1-year (VAS: 0.83±1.09; 4.80±1.58; P<0.05) follow-up. The pain-improved and worsened groups had a significant difference in tumor size and hemilaminectomy removal segments at 1-month and 1-year follow-up, but A-train occurrence on electromyography could only be seen as a statistical difference in the 1-month follow-up. Logistic regression analysis revealed that tumor size was an independent risk factor for postoperative lower back pain deterioration.

Conclusion

The hemilaminectomy approach is a safe and effective method that can dramatically relieve pain in spinal lumbar schwannoma resection. Tumor size is an independent risk factor for postoperative lower back pain. A-train on spontaneous electromyography has been shown to be a reliable predictive factor for the evaluation of postoperative lower back pain. However, further detailed analysis of A-train characteristics can provide a more accurate warning during surgery.

Spinal intradural extramedullary tumors: microscopic keyhole resection with the focus on intraoperative neurophysiological monitoring and long-term outcome

OBJECTIVE

Spinal schwannomas (SS) and spinal meningiomas (SM) account for most intradural extramedullary (IDEM) tumors. These tumors are usually benign lesions, which generally respond favorably to surgical excision. Few studies up to now tried to determine the long-term outcome after minimally invasive surgery (MIS) with multimodal intraoperative neurophysiological monitoring (IONM) for IDEM tumors. The aim of this study was to present one of the largest case series with special regard to IONM findings and long-term outcome after MIS-keyhole surgery with a tubular retractor system.

METHODS

Between January 2013 and August 2018, 87 patients with IDEM tumors who underwent tumor removal surgery via MIS-keyhole approach under multimodal IONM were retrospectively reviewed. The neurological status was assessed using a modified McCormick grading scale pre- and postoperatively. Multimodal IONM consisted of motor evoked potentials (MEP), somatosensory evoked potentials (SEP), and electromyography (EMG). Both short-term and long-term clinical evaluations as well as patients' medical files were retrospectively analyzed.

RESULTS

Surgeries were performed for resection of SS in 49 patients and SM in 38 patients. Tumor locations were cervical in 16.1%, thoracic in 48.3%, thoracolumbar in 4.6%, lumbar 31%. Critical IONM changes were detected in 9 operations (10.3%) in which there were 2 SEPs, 5 MEPs, and 2 EMG events. Three IONM changes (2 MEPs, 1 EMG) were turned out to be transient change in nature since they were resolved in a short time when immediate corrective actions were initiated. Six patients with permanent IONM changes (2SEPs, 3MEPs, 1EMG event), all deficits had resolved during hospitalization or on short -term follow-up evaluation. Sensitivity, specificity, and positive and negative predicted values of IONM were 100, 96, 67, and 100%, respectively. Gross total resection rate was 100%, and a stable or improved McCormick grade exhibited in all patients. No tumor recurrence and no spinal instability were found in the long-term follow-up evaluation (mean 5.2 ± 2.9 years postoperatively). Overall, 94% of patients were either satisfied or very satisfied with their operation, and 93% patients reported excellent or good general clinical outcome according to Odom's criteria.

CONCLUSION

MIS-keyhole surgery with multimodal IONM for IDEM tumors enables a high level of satisfaction and a satisfying long-term clinical and surgical outcome.

Need for head and neck repositioning to restore electrophysiological signal changes at positioning for cervical myelopathy surgery

OBJECTIVE

To evaluate the incidence of significant intraoperative electrophysiological signal changes during surgical positioning, and to assess the effectiveness of head and neck repositioning on the restoration of signals, among patients undergoing surgery for cervical myelopathy.

MATERIAL AND METHODS

We used multimodal intraoperative monitoring (somatosensory [SEP] and motor evoked potentials [MEP] and spontaneous electromyography) before and after patients' positioning in a consecutive cohort of 103 patients operated for symptomatic cervical myelopathy. Significant changes were defined as>50% attenuation in amplitude or>10% increase in latency of SEP, or abolishment or 50-80% attenuation of MEP.

RESULTS

Out of 103 patients (34.9% female, median age 54.5 years) 88 underwent laminectomy (85.4%) and 15 (14.6%) anterior approach. At the time of positioning, signal alterations occurred in 44 patients (42.7%), yet only 11 patients (10.7%) showed alarming changes. Immediate neck repositioning of these resulted in complete (n=6) or partial (n=4) restoration of potentials, yielding no postoperative deficits. The patient in which signals could not be restored after repositioning resulted in added postoperative deficit. The accuracy (true positives plus true negatives) of monitoring to detect new neurological deficits was 99.0% (102/103) for the entire cohort, and 100% (11/11) for those showing significant changes at the moment of positioning. Overall, only 1 patient, with non-significant SEP attenuation, experienced a new postoperative deficit, yielding a 0.97% rate of false negatives.

CONCLUSION

Among patients undergoing surgery for cervical myelopathy, 10.7% showed alarming electrophysiological signal changes at the time of positioning. Immediate repositioning of the neck resulted in near always restoration of potentials and avoidance of added neurological damage. Complete or partial restoration of potentials after repositioning yielded no postoperative deficits.

Multimodal Neuroelectrophysiological Monitoring Combined with Robot-Assisted Placement of a Transiliac–Transsacral Screw for the Treatment of Transforaminal Sacral Fractures

Objective

This study aimed to evaluate the safety and efficacy of the fixation of transforaminal sacral fractures using TiRobot-assisted transiliac-transsacral (TITS) screws under multimodal neuroelectrophysiological monitoring (MNM).

Methods

From January 2019 to May 2021, 22 patients (17 male and 5 female patients) with transforaminal sacral fractures who were treated with closed reduction and placement of TiRobot-assisted TITS screws under MNM were retrospectively evaluated. The average age of the patients was 43.32 ± 11.40 years (range: 19–63). The patients received MNM, including somatosensory-evoked potentials (SEPs), motor-evoked potentials (MEPs), and electromyographic monitoring (EMG), prior to surgery, during closed reduction and the placement of the guidewire and TITS screw, and at the end of surgery. The operation was adjusted according to the MNM results.

Results

Overall, 22 TITS screws were inserted in 22 patients, including 5 TITS screws in the S1 body and 17 TITS screws in the S2 body. The average time needed for screw placement was 27.95 ± 6.84 mins, and the average frequency of X-ray fluoroscopy exposures was 31.00 ± 5.56 for each patient. Anterior ring fixation was performed in 4 patients using an external fixator, in 5 patients using cannulated screws, and in 13 patients using reconstruction plates. The mean follow-up time was 14.46 ± 2.46 months (12–20 months). Tornetta and Matta radiographic outcomes were excellent in 10 patients, good in 9 patients, fair in 2 patients, and poor in 1 patient. The proportion of excellent and good ratings was 86.36%. At the final follow-up, the average Majeed score was 82.18 ± 14.52, with clinical outcomes that were excellent in 9 patients, good in 9 patients, fair in 1 patient, and poor in 3 patients. The proportion of excellent and good ratings was 82.82%. Preoperatively, the amplitude of the SEP on the injured side was lower than that on the contralateral side before reduction in 9 patients (>50%). In this study, no screw was mistakenly inserted into the sacral canal, and no surgical site infection occurred.

Conclusion

MNM combined with TiRobot assistance can safely implant TITS screws and can effectively identify the neurological function of patients under anesthesia and reduce iatrogenic nerve injury.

Intraoperative neuromonitoring during surgery for lumbar stenosis

The indications for neuromonitoring during lumbar stenosis surgery are defined by the risks associated with patient positioning, the approach, decompression of neural elements, deformity correction, and instrument implantation. The routine use of EMG and SEP alone during lumbar stenosis surgery is no longer supported by the literature. Lateral approach neuromonitoring with EMG only is also suspect. Lumbar stenosis patients often present with multiple co-morbidities which put them at risk during routine pre-surgical positioning. Frequently encountered morbid obesity and/or diabetes mellitus may play a role in monitorable and preventable brachial plexopathy after "superman" positioning or femoral neuropathy from groin pressure after prone positioning, for example. Deformity correction in lumbar stenosis surgery often demands advanced implementation of multiple neuromonitoring modalities: EMG, SEP, and MEP. Because the bulbocavernosus reflex detects the function of the conus medullaris and sacral somato afferent/efferent fibers of the cauda equina, it may also be recorded. The recommendation to record pedicle screw thresholds has become more nuanced as surgeon dependence on 3D imaging, navigation, and robotics has increased. Neuromonitoring in lumbar stenosis surgery has been subject mainly to uncontrolled case series; prospective cohort trials are also needed.

Intramedullary spinal cord and filum tumours-long-term outcome: single institution case series

BACKGROUND

Intramedullary spinal cord tumours are rare and account for about 2-4% of primary CNS tumours. Ependymomas and astrocytomas are most frequent. The aim of this study was to evaluate the long-term neurological outcome, quality of life (QoL), survival, need for additional treatment and frequency of neuropathic pain in a patient group treated at a tertiary university hospital.

METHOD

Retrospective descriptive study of 52 long-term survivors with intramedullary or filum tumours consenting to participate in this study. Fifty-six operations were performed in 48 patients. Clinical and radiological follow-up period was 113 and 117 months, respectively.

RESULTS

Good neurological outcome (ASIA score D or E, modified McCormick grade 1 or 2) was achieved in 88%. We found two negative prognostic factors in regards of severe disability which were large craniocaudal tumour size (p = 0.004) and histologic verified astrocytomas (p = 0.002). SF-36 results showed significantly lower results on all five subdomains concerning physical function, whereas scores for mental health and role emotional showed no significant differences compared to Norwegian norms. Ten patients including all astrocytoma patients, one primitive neuroectodermal tumour and three recurrent tumours of filum terminale had adjuvant therapy. None of the patients with intramedullary ependymoma had adjuvant therapy. Neuropathic pain was present in 54% of patients at the last follow-up.

CONCLUSION

This series shows that good results can be obtained with surgery for intramedullary tumours, even without perioperative neurophysiological monitoring. Multicentre studies are needed for further evaluation of negative and positive prognostic factors to further improve outcome.

Intraoperative evoked potential techniques

There are many recent advances in intraoperative evoked potential techniques for mapping and monitoring neural function during surgery. In particular, somatosensory evoked potential optimization speeds surgical feedback, motor evoked potentials provide selective motor system information, and new visual evoked potential methods promise reliable visual system monitoring. This chapter reviews these advances and provides a comprehensive background for understanding their context and importance.

Need for head and neck repositioning to restore electrophysiological signal changes at positioning for cervical myelopathy surgery

OBJECTIVE

To evaluate the incidence of significant intraoperative electrophysiological signal changes during surgical positioning, and to assess the effectiveness of head and neck repositioning on the restoration of signals, among patients undergoing surgery for cervical myelopathy.

MATERIAL AND METHODS

We used multimodal intraoperative monitoring (somatosensory [SEP] and motor evoked potentials [MEP] and spontaneous electromyography) before and after patients' positioning in a consecutive cohort of 103 patients operated for symptomatic cervical myelopathy. Significant changes were defined as>50% attenuation in amplitude or>10% increase in latency of SEP, or abolishment or 50-80% attenuation of MEP.

RESULTS

Out of 103 patients (34.9% female, median age 54.5 years) 88 underwent laminectomy (85.4%) and 15 (14.6%) anterior approach. At the time of positioning, signal alterations occurred in 44 patients (42.7%), yet only 11 patients (10.7%) showed alarming changes. Immediate neck repositioning of these resulted in complete (n=6) or partial (n=4) restoration of potentials, yielding no postoperative deficits. The patient in which signals could not be restored after repositioning resulted in added postoperative deficit. The accuracy (true positives plus true negatives) of monitoring to detect new neurological deficits was 99.0% (102/103) for the entire cohort, and 100% (11/11) for those showing significant changes at the moment of positioning. Overall, only 1 patient, with non-significant SEP attenuation, experienced a new postoperative deficit, yielding a 0.97% rate of false negatives.

CONCLUSION

Among patients undergoing surgery for cervical myelopathy, 10.7% showed alarming electrophysiological signal changes at the time of positioning. Immediate repositioning of the neck resulted in near always restoration of potentials and avoidance of added neurological damage. Complete or partial restoration of potentials after repositioning yielded no postoperative deficits.

Multimodal Intraoperative Spinal Cord Monitoring during Spinal Deformity Surgery: Efficacy, Diagnostic Characteristics, and Algorithm Development

OBJECTIVE

This study aims to present the diagnostic characteristics of multimodal intraoperative monitoring (IOM) in spinal deformity surgery and to define and categorise the neuromonitoring events, as well as propose an algorithm of action.

MATERIALS AND METHODS

We reviewed 1,155 consecutive patients (807 female, 348 male) who underwent deformity correction using standardised perioperative care, cortical/cervical somatosensory evoked potentials (SSEPs), and upper/lower limb transcranial electrical motor evoked potential (MEPs) by a single surgeon. The mean age at surgery was 13.8 years (range 10-23.3). We categorised IOM events as true, transient true, and false positive or negative. Diagnostic performance criteria were calculated.

RESULTS

The most common diagnosis was adolescent idiopathic scoliosis in 717 (62%) patients. We identified 3 true positive monitoring events occurring in 2 patients (0.17%), 8 transient true positive (0.69%), and 8 transient false positive events (0.69%). There were no false negative events and no patient had postoperative neurological complications. The multimodal IOM technique had a sensitivity of 100%, specificity of 99.3%, positive predictive value of 55.6%, and negative predictive value of 100%. Sensitivity was 100% for MEPs and multimodal monitoring compared to 20% for cortical or cervical SSEPs. The frequency of true or transient true positive events was higher (p = 0.07) in Scheuermann's kyphosis (3/91 patients, 3.3%) compared to adolescent idiopathic scoliosis (6/717 patients, 0.84%).

CONCLUSION

Multimodal IOM is highly sensitive and specific for spinal cord injury. This technique is reliable for the assessment of the condition of the spinal cord during major deformity surgery. We propose an algorithm of intraoperative action to allow close cooperation between the surgical, anaesthetic, and neurophysiology teams and to prevent neurological deficits.

Clinical Significance of Improved Intraoperative Neurophysiological Monitoring Signal during Spine Surgery: A Retrospective Study of a Single-Institution Prospective Cohort

Study Design

Retrospective case series.

Purpose

We reviewed the cases that showed significant improvement of intraoperative neurophysiological monitoring (IONM) signals during spine surgery to assess whether there is a correlation with signal improvement and postoperative clinical status and its clinical significance.

Overview of Literature

To reduce the risk of neural injury, many spine surgeons are using multimodality IONM. Although many studies attempted to identify valid alarm criteria for predicting postoperative neurologic deterioration, studies concerning the improvement of IONM signals are rare.

Methods

We reviewed all spine surgery cases with IONM data treated at our department between January 2013 and May 2017. We found cases showing significant IONM signal improvements. We prospectively analyzed the neurological and clinical outcomes of these patients and compared outcomes pre- and postoperatively.

Results

Among 317 cases with the IONM data, we found 29 cases that showed IONM signal improvement compared with baseline. There were 27 cases of compressive myelopathy: 22 had a degenerative cause at the cervical spine, and five, at the thoracic spine. There were two cases of huge neurogenic tumor each at the craniovertebral junction and at the lumbar spine. Both motor-evoked potentials (MEPs) and somatosensory-evoked potentials (SSEPs) signals were improved in six cases, only the MEPs signal improved in 10, and only SSEP signal improved in 13 cases. All cases showed the IONM signal improvement consistently after the decompression procedure during surgery. All patients had a significant improvement in neurological function and subjective symptoms, and none had neurologic deterioration postoperatively.

Conclusions

Improvement of IONM signals during surgery may indicate that no unrecognized neural injury occurred during surgery and a favorable postoperative neurological outcome can be expected.

Practice guidelines for the supervising professional: intraoperative neurophysiological monitoring

The American Society of Neurophysiological Monitoring (ASNM) was founded in 1989 as the American Society of Evoked Potential Monitoring. From the beginning, the Society has been made up of physicians, doctoral degree holders, Technologists, and all those interested in furthering the profession. The Society changed its name to the ASNM and held its first Annual Meeting in 1990. It remains the largest worldwide organization dedicated solely to the scientifically-based advancement of intraoperative neurophysiology. The primary goal of the ASNM is to assure the quality of patient care during procedures monitoring the nervous system. This goal is accomplished primarily through programs in education, advocacy of basic and clinical research, and publication of guidelines, among other endeavors. The ASNM is committed to the development of medically sound and clinically relevant guidelines for the performance of intraoperative neurophysiology. Guidelines are formulated based on exhaustive literature review, recruitment of expert opinion, and broad consensus among ASNM membership. Input is likewise sought from sister societies and related constituencies. Adherence to a literature-based, formalized process characterizes the construction of all ASNM guidelines. The guidelines covering the Professional Practice of intraoperative neurophysiological monitoring were initially published January 24th, 2013, and subsequently that document has undergone review and revision to accommodate broad inter- and intra-societal feedback. This current version of the ASNM Professional Practice Guideline was fully approved for publication according to ASNM bylaws on February 22nd, 2018, and thus overwrites and supersedes the initial guideline.

Intraoperative Neurophysiologic Monitoring for Lumbar Intradural Schwannomas: Does It Affect Clinical Outcome?

OBJECTIVE

Intraoperative multimodal neuromonitoring (IONM) is considered valuable for the early detection and prevention of any neurologic compromise during spine surgery. It has also become the standard of care at many institutions to improve the surgical outcome and be a safety net for both clinical and medicolegal concerns.

METHODS

Our experience and outcomes in 46 consecutive cases of lumbar intradural schwannoma resection were reviewed with respect to clinical outcomes and patient safety, before and after the integration of IONM into our clinical practice.

RESULTS

Total surgical resection of schwannomas in the lumbar spine led to improved health-related quality of life for patients. The standard technique for microsurgical resection of schwannomas requires identifying and resecting the fiber of origin for the schwannoma, guided with triggered electromyographic monitoring. However, whether this changed the surgical strategy, because spinal roots that gave rise to the schwannoma were frequently found to be nonfunctional during surgery, remains unclear. In our series of 46 patients, we did not recognize any additional motor deficit after the surgery, regardless of the use of IONM.

CONCLUSIONS

Despite our analysis proving no difference in clinical outcomes with or without the use of IONM during surgical excision of lumbar schwannomas, we still prefer using IONM as a standard approach. It adds to the confidence and ease of mind of the surgeon during resection and also provides valuable data in cases of medicolegal disputes. However, it comes with an increased cost and lengthened surgical procedure.

The impact and value of uni- and multimodal intraoperative neurophysiological monitoring (IONM) on neurological complications during spine surgery: a prospective study of 2728 patients

PURPOSE

We compared the value of different uni- and multimodal intraoperative neurophysiological monitoring (IONM) methods on the detection of neurological complications during spine surgery.

METHODS

IONM data derived from sensory spinal and cortical evoked potentials combined with continuous electromyography monitoring, motor evoked potentials and spinal recording were evaluated in relation to subsequent post-operative neurological changes. Patients were categorised based on their true-positive or true-negative post-operative neurological status.

RESULTS

In 2728 consecutive patients we had 909 (33.3%) IONM alerts. We had 8 false negatives (0.3%) with post-operative radicular deficit that completely recovered within 3 months, except for one. There was no false negative for spinal cord injury. 107 were true positives, and 23 were false positives. Multimodal IONM sensitivity and specificity were 93.0% and 99.1%, respectively. The frequency of neurological complications including minor deficits was 4.2% (n = 115), of which 0.37% (n = 10) were permanent. Analysis of the single IONM modalities varied between 13 and 81% to detect neurological complications compared with 93% when using all modalities.

CONCLUSION

Multimodal IONM is more effective and accurate in assessing spinal cord and nerve root function during spine surgeries to reduce both neurological complications and false-negative findings compared to unimodal monitoring. We recommend multimodal IONM in all complex spine surgeries. These slides can be retrieved from Electronic Supplementary Material.

Do intra-operative neurophysiological changes predict functional outcome following decompressive surgery for lumbar spinal stenosis? A prospective study

Background

To analyse the relation between immediate intraoperative neurophysiological changes during decompression and clinical outcome in a series of patients with lumbar spinal stenosis (LSS) undergoing surgery.

Methods

Twenty-four patients with neurogenic intermittent claudication (NIC) due to LSS undergoing decompressive surgery were prospectively studied. Intra operative trans-cranial motor evoked potentials (tcMEPs) were recorded before and immediately after surgical decompression. Lower limb normalised tcMEP improvement was used as primary neurophysiological outcome. Clinical outcome was assessed using the Zurich Claudication Questionnaire (ZCQ) self-assessment score, before surgery (baseline) and at an average of 8 and 29 months post-operatively.

Results

We found a moderate positive correlation between tcMEP changes and ZCQ at early follow-up (R=0.36). At late follow-up no correlation was found between intra-operative tcMEP and ZCQ changes. Dichotomizing the data showed a statistically significant relationship between tcMEP improvement and better functional outcome at early follow-up (P=0.013) but not at later follow-up (P=1).

Conclusions

Our findings suggest that intra-operative neurophysiological improvement during decompressive surgery may predict a better clinical outcome at early follow-up although this is not applicable to late follow-up possibly due to the observed erosion of functional improvement with time.

Intraoperative neurophysiological monitoring during the surgery of spinal arteriovenous malformation: sensitivity, specificity, and warning criteria

OBJECTIVE

The incidence of spinal arteriovenous malformation (SAVM) is low, but its treatment is challenging. Intraoperative neurophysiological monitoring (IONM) for intramedullary tumors has been a benchmark in neurosurgery. This study aimed to determine the sensitivity, specificity, and warning criteria of IONM for SAVM surgeries.

MATERIALS AND METHODS

From November 2012 to January 2016, 55 patients underwent SAVM surgery with IONM at the Neurosurgery Department of Xuanwu Hospital of Capital Medical University, China. Modified McCormick grading scale was used to evaluate patients' function 3 days before and immediately, 1 week, 3 months, and 6 months after surgery. IONM was performed including somatosensory evoked potential (SEP), trans-cranial motor-evoked potential (tcMEP), and electromyography (EMG). All patients were followed up every 3 or 6 months.

RESULTS

The SAVM locations were cervical spine in 15 (27.3%) patients, thoracic in 24 (43.6%), thoracolumbar in 12 (21.8%), and lumbar in 4 (7.3%). TcMEP and SEP were could be monitored in 53 (96.4%) and 33 (60.0%) patients, respectively. Using >80% irreversible amplitude reduction of the tcMEP as threshold, the sensitivity, specificity, and positive and negative predictive values were 77.3%, 87.1%, 81.0%, and 84.4%, respectively; using >50% irreversible amplitude reduction of the tcMEP as the warning criterion, these values were 81.8% 74.2%, 69.2%, and 85.2%, respectively.

CONCLUSION

In practical applications of tcMEP for SAVM surgeries, the 50% irreversible amplitude reduction of the tcMEP criterion can be used to warn the surgeon, while the >80% criterion can be used to stop the operation in order to avoid neurological impairments.

A randomized crossover study of the effects of lidocaine on motor- and sensory-evoked potentials during spinal surgery

BACKGROUND CONTEXT

Lidocaine has emerged as a useful adjuvant anesthetic agent for cases requiring intraoperative monitoring of motor-evoked potentials (MEPs) and somatosensory-evoked potentials (SSEPs). A previous retrospective study suggested that lidocaine could be used as a component of propofol-based intravenous anesthesia without adversely affecting MEP or SSEP monitoring, but did not address the effect of the addition of lidocaine on the MEP and SSEP signals of individual patients.

PURPOSE

The purpose of this study was to examine the intrapatient effects of the addition of lidocaine to balanced anesthesia on MEPs and SSEPs during multilevel posterior spinal fusion.

STUDY DESIGN

This is a prospective, two-treatment, two-period crossover randomized controlled trial with a blinded primary outcome assessment.

PATIENT SAMPLE

Forty patients undergoing multilevel posterior spinal fusion were studied.

OUTCOME MEASURES

The primary outcome measures were MEP voltage thresholds and SSEP amplitudes. Secondary outcome measures included isoflurane concentrations and hemodynamic parameters.

METHODS

Each participant received two anesthetic treatments (propofol 50 mcg/kg/h and propofol 25 mcg/kg/h+lidocaine 1 mg/kg/h) along with isoflurane, ketamine, and diazepam. In this manner, each patient served as his or her own control. The order of administration of the two treatments was determined randomly.

RESULTS

There were no significant within-patient differences between MEP threshold voltages or SSEP amplitudes during the two anesthetic treatments.

CONCLUSIONS

Lidocaine may be used as a component of balanced anesthesia during multilevel spinal fusions without adversely affecting the monitoring of SSEPs or MEPs in individual patients.

Magnetospinography visualizes electrophysiological activity in the cervical spinal cord

Diagnosis of nervous system disease is greatly aided by functional assessments and imaging techniques that localize neural activity abnormalities. Electrophysiological methods are helpful but often insufficient to locate neural lesions precisely. One proposed noninvasive alternative is magnetoneurography (MNG); we have developed MNG of the spinal cord (magnetospinography, MSG). Using a 120-channel superconducting quantum interference device biomagnetometer system in a magnetically shielded room, cervical spinal cord evoked magnetic fields (SCEFs) were recorded after stimulation of the lower thoracic cord in healthy subjects and a patient with cervical spondylotic myelopathy and after median nerve stimulation in healthy subjects. Electrophysiological activities in the spinal cord were reconstructed from SCEFs and visualized by a spatial filter, a recursive null-steering beamformer. Here, we show for the first time that MSG with high spatial and temporal resolution can be used to map electrophysiological activities in the cervical spinal cord and spinal nerve.

Intraoperative spinal cord monitoring: Lesional level diagnosis

BACKGROUND

In spinal deformity surgery, iatrogenic spinal cord injury is the most feared complication. Intraoperative monitoring (IOM) of the spinal cord assesses its functional integrity and allows significant reduction of the rate of spinal cord injury.

HYPOTHESIS

In case of severe IOM alert, lesional level diagnosis constitutes supplementary and useful information.

MATERIAL AND METHODS

This study was retrospective and monocentric. In our institution, 1062 pediatric spinal deformity surgeries have been monitored since 2004. We review the records of the six patients who presented a severe and prolonged IOM alert with lesional level determination. Somatosensory evoked potentials (SSEP), neurogenic mixed evoked potentials (NMEP) and D-waves were performed. In cases of IOM alert, sequentially moving an epidural electrode along the spinal cord allows lesional level determination, using this electrode either for stimulation or recording.

RESULTS

Six patients, aged 12 to 17 years, characterized by severe IOM alerts during spinal deformity surgery are reported. Postoperative neurological examination was normal for five out of six cases. For patient 2, lesional level diagnosis allowed to determine a bi-laminar claw between T2 and T3 as the etiology of IOM alert. This IOM alert was delayed in time, being detectable only 30minutes after the placement of this claw. Postoperative neurological examination was normal. For patient 6, a Stagnara wake-up test demonstrated paraplegia. Lesional level was established. Following corrective surgical maneuvers, postoperative neurologic deficit was limited to a pyramidal syndrome in one lower limb. Postoperative MRI demonstrated a spinal cord lesion at the determined lesional level.

CONCLUSION

During an IOM alert, lesional level determination allows localization of spinal cord dysfunction. This data, obtainable whatever the IOM device, constitutes supplementary information in order to rapidly identify the etiology of IOM alert and thus to react in the most appropriate way.

LEVEL OF EVIDENCE

IV, retrospective study.

Outcome of L5 radiculopathy after reduction and instrumented transforaminal lumbar interbody fusion of high-grade L5-S1 isthmic spondylolisthesis and the role of intraoperative neurophysiological monitoring

PURPOSE

To evaluate the incidence and course of iatrogenic L5 radiculopathy after reduction and instrumented fusion of high-grade L5-S1 isthmic spondylolisthesis and the role of intraoperative neurophysiological monitoring (IONM).

METHODS

Consecutive patients treated for high-grade spondylolisthesis with IONM from 2005 to 2013 were screened for eligibility. Prospectively collected clinical and surgical data as well as radiographic outcomes were analyzed retrospectively. Patients completed the multidimensional Core Outcome Measures Index (COMI) before and at 3, 12, and 24 months after surgery.

RESULTS

Seventeen patients were included, with a mean age of 26.3 (±9.5) years. Mean preoperative L5-S1 slip was 72% (±21%) and was reduced to 19% (±13%) postoperatively. Mean loss of reduction at last follow-up [mean 19 months (±14, range 3-48 months)] was 3% (±4.3%). Rate of new L5 radiculopathy with motor deficit (L5MD) after surgery was 29% (five patients). Four patients fully recovered after 3 months, one patient was lost to neurologic follow-up. IONM sensitivity and specificity for postoperative L5MD was 20 and 100%, respectively. COMI, back pain and leg pain scores showed significant (p < 0.001) improvements at 3 months postoperatively, which were retained up to 24 months postoperatively.

CONCLUSIONS

Transient L5 radiculopathy after reduction and instrumented fusion of high-grade spondylolisthesis is frequent. With IONM the risk of irreversible L5 radiculopathy is minimal. If IONM signal changes recover, full clinical recovery is expected within 3 months. Overall, patient-reported outcome of reduction and instrumented fusion of high-grade spondylolisthesis showed clinically important improvement.

Validity and utility of monopolar spinal cord stimulation in pediatric scoliosis surgery

PURPOSE

To assess the validity and utility of monopolar stimulation (between a peridural needle and a large adhesive anode placed in the sternal area) for intraoperative monitoring in scoliosis surgery.

METHODS

This procedure was assessed during 41 operations involving either arthrodesis with posterior instrumentation or a Vertical Expandable Prosthetic Titanium Rib (VEPTR). Responses evoked by monopolar stimulation were compared with those evoked by bipolar stimulation between two epidural needle electrodes. Potentials evoked by monopolar stimulation in the upper limbs were compared with those evoked in the lower limbs during the same stimulation procedure.

RESULTS

Monopolar stimulation yielded equivalent and, if anything, more stable responses in the lower limbs. Recording in the upper limbs was satisfactory and allowed a decrease in responses to be detected in two patients. Acceptable thresholds for changes in amplitude relative to baseline were 40 % for upper limbs and 30 % for lower limbs.

CONCLUSIONS

Monopolar stimulation can be used to monitor the spinal cord during surgery for scoliosis correction. This procedure is more convenient for the surgeon and allows for the combined recording of responses in all four limbs, which can be useful in the case of surgical techniques such as those involving a VEPTR.

Intraoperative neurophysiological monitoring during resection of intradural extramedullary spinal cord tumors: experience with 100 cases

BACKGROUND

Intradural-extramedullary spinal cord tumor surgery is common. Unlike intramedullary spinal cord tumor surgery, where intraoperative neurophysiological monitoring (IONM) has been described extensively, the application of IONM has not been described in this context, and its relevance has not been investigated.

METHODS

From 2001 to 2012, 100 patients underwent intradural-extramedullary spinal cord tumor resection with IONM. Preoperative and postoperative clinical evaluations were completed retrospectively, using a modified McCormick grading scale and correlated with IONM monitorability and dynamics. IONM consisted of transcranial motor evoked potentials (tcMEP), spinal (D wave) and muscle generators, somatosensory evoked potentials (SSEP), and electromyography (EMG). Both short-term and long-term clinical evaluations were performed. Patient demographics, tumor type, span, location, and morphologic complexity were analyzed.

RESULTS

Surgeries were performed for resection of schwannomas (33 %), meningiomas (22 %), ependymomas (12 %), and other pathologies (20 %); pathology was unknown in 13 % of patients. Tumor locations were cervical in 21 %, thoracic in 46 %, thoracolumbar in 7 %, lumbar 20 %, and not specified in 6 %. Tumors spanned an average of 2.2 spinal levels. Monitorability was 97 and 67 % with tcMEP and SSEP modalities respectively. D waves were monitorable in 73 % of attempts. Intraoperative tcMEP changes were reported in 29 cases with 14 resolved intraoperatively, There were one false-negative outcome and five true-positive outcomes. For SSEP, 13 changes were noted and three resolved; there were three false-negative results and one true-positive result. For D wave monitoring there were two intraoperative changes with none resolved leading to one false negative and one true positive result. With a multimodality approach incorporating any change in evoked potential, IONM demonstrated sensitivity of 0.82, specificity of 0.95, positive predictive value of 0.82, and a negative predictive value of 0.95.

CONCLUSIONS

IONM is feasible and useful in the context of intradural-extramedullary spinal cord surgery for identifying iatrogenic injury to the spinal cord.

Best Practices in Intraoperative Neuromonitoring in Spine Deformity Surgery: Development of an Intraoperative Checklist to Optimize Response

STUDY DESIGN

Consensus-based creation of a checklist and guideline.

OBJECTIVE

To develop a consensus-based checklist to guide surgeon responses to intraoperative neuromonitoring (IONM) changes in patients with a stable spine and to develop a consensus-based best practice guideline for IONM practice in the United States.

SUMMARY OF BACKGROUND DATA

Studies show that checklists enhance surgical team responses to crisis situations and improve patient outcomes. Currently, no widely accepted guidelines exist for the response to IONM changes in spine deformity surgery.

METHODS

After a literature review of risk factors and recommendations for responding to IONM changes, 4 surveys were administered to 21 experienced spine surgeons and 1 neurologist experienced in IONM. Areas of equipoise were identified and the nominal group process was used to determine items to be included in the checklist. The authors reevaluated and modified the checklist at 3 face-to-face meetings over 12 months, including a period of clinical validation using a modified Delphi process. The group was also surveyed on current IONM practices at their institutions. This information and existing IONM position statements were used to create the IONM best practice guideline.

RESULTS

Consensus was reached for the creation of 5 checklist headings containing 26 items to consider in the response to IONM changes. Consensus was reached on 5 statements for inclusion in the best practice guideline; the final guideline promotes a team approach and makes recommendations aimed at decreasing variability in neuromonitoring practices.

CONCLUSIONS

The final products represent the consensus of a group of expert spine surgeons. The checklist includes the most important and high-yield items to consider when responding to IONM changes in patients with a stable spine, whereas the IONM guideline represents the group consensus on items that should be considered best practice among IONM teams with the appropriate resources.

Predicting intraoperative feasibility of combined TES-mMEP and cSSEP monitoring during scoliosis surgery based on preoperative neurophysiological assessment

BACKGROUND CONTEXT

Combined monitoring of muscle motor evoked potentials elicited by transcranial electric stimulation (TES-mMEP) and cortical somatosensory evoked potentials (cSSEPs) is safe and effective for spinal cord monitoring during scoliosis surgery. However, TES-mMEP/cSSEP is not always feasible. Predictors of feasibility would help to plan the monitoring strategy.

PURPOSE

To identify predictors of the feasibility of TES-mMEP/cSSEP during scoliosis surgery.

STUDY DESIGN/SETTING

Prospective cohort study in a clinical neurophysiology unit and pediatric orthopedic department of a French university hospital.

PATIENT SAMPLE

A total of 103 children aged 2 to 19 years scheduled for scoliosis surgery.

OUTCOME MEASURES

Feasibility rate of intraoperative TES-mMEP/cSSEP monitoring.

METHODS

All patients underwent a preoperative neurological evaluation and preoperative mMEP and cSSEP recordings at both legs. For each factor associated with feasibility, we computed sensitivity, specificity, positive predictive value (PPV), and negative predictive value. A decision tree was designed.

RESULTS

Presence of any of the following factors was associated with 100% feasibility, 100% specificity, and 100% PPV: idiopathic scoliosis, normal preoperative neurological findings, and normal preoperative mMEP and cSSEP recordings. Feasibility was 0% in the eight patients with no recordable mMEPs or cSSEPs during preoperative testing. A decision tree involving three screening steps can be used to identify patients in whom intraoperative TES-mMEP/cSSEP is feasible.

CONCLUSIONS

Preoperative neurological and neurophysiological assessments are helpful for identifying patients who can be successfully monitored by TES-mMEP/cSSEP during scoliosis surgery.

Individual differences in transcranial electrical stimulation current density

Transcranial electrical stimulation (TCES) is effective in treating many conditions, but it has not been possible to accurately forecast current density within the complex anatomy of a given subject's head. We sought to predict and verify TCES current densities and determine the variability of these current distributions in patient-specific models based on magnetic resonance imaging (MRI) data. Two experiments were performed. The first experiment estimated conductivity from MRIs and compared the current density results against actual measurements from the scalp surface of 3 subjects. In the second experiment, virtual electrodes were placed on the scalps of 18 subjects to model simulated current densities with 2 mA of virtually applied stimulation. This procedure was repeated for 4 electrode locations. Current densities were then calculated for 75 brain regions. Comparison of modeled and measured external current in experiment 1 yielded a correlation of r = .93. In experiment 2, modeled individual differences were greatest near the electrodes (ten-fold differences were common), but simulated current was found in all regions of the brain. Sites that were distant from the electrodes (e.g. hypothalamus) typically showed two-fold individual differences. MRI-based modeling can effectively predict current densities in individual brains. Significant variation occurs between subjects with the same applied electrode configuration. Individualized MRI-based modeling should be considered in place of the 10-20 system when accurate TCES is needed.

Intraoperative neurophysiologic monitoring in spine surgery. Developments and state of the art in France in 2011

Intraoperative spinal cord monitoring consists in a subcontinuous evaluation of spinal cord sensory-motor functions and allows the reduction the incidence of neurological complications resulting from spinal surgery. A combination of techniques is used: somatosensory evoked potentials (SSEP), motor evoked potentials (MEP), neurogenic motor evoked potentials (NMEP), D waves, and pedicular screw testing. In absence of intraoperative neurophysiological testing, the intraoperative wake-up test is a true form of monitoring even if its latency long and its precision variable. A 2011 survey of 117 French spinal surgeons showed that only 36% had neurophysiological monitoring available (public healthcare facilities, 42%; private facilities, 27%). Monitoring can be performed by a neurophysiologist in the operating room, remotely using a network, or directly by the surgeon. Intraoperative alerts allow real-time diagnosis of impending neurological injury. Use of spinal electrodes, moved along the medullary canal, can determine the lesion level (NMEP, D waves). The response to a monitoring alert should take into account the phase of the surgical intervention and does not systematically lead to interruption of the intervention. Multimodal intraoperative monitoring, in presence of a neurophysiologist, in collaboration with the anesthesiologist, is the most reliable technique available. However, no monitoring technique can predict a delayed-onset paraplegia that appears after the end of surgery. In cases of preexisting neurological deficit, monitoring contributes little. Monitoring of the L1-L4 spinal roots also shows low reliability. Therefore, monitoring has no indication in discal and degenerative surgery of the spinal surgery. However, testing pedicular screws can be useful. All in all, thoracic and thoracolumbar vertebral deviations, with normal preoperative neurological examination are currently the essential indication for spinal cord monitoring. Its absence in this indication is a lost opportunity for the patient. If neurophysiological means are not available, intraoperative wake-up test is a minimal obligation.

Intraoperative motor evoked potential monitoring - a position statement by the American Society of Neurophysiological Monitoring

The following intraoperative MEP recommendations can be made on the basis of current evidence and expert opinion: (1) Acquisition and interpretation should be done by qualified personnel. (2) The methods are sufficiently safe using appropriate precautions. (3) MEPs are an established practice option for cortical and subcortical mapping and for monitoring during surgeries risking motor injury in the brain, brainstem, spinal cord or facial nerve. (4) Intravenous anesthesia usually consisting of propofol and opioid is optimal for muscle MEPs. (5) Interpretation should consider limitations and confounding factors. (6) D-wave warning criteria consider amplitude reduction having no confounding factor explanation: >50% for intramedullary spinal cord tumor surgery, and >30-40% for peri-Rolandic surgery. (7) Muscle MEP warning criteria are tailored to the type of surgery and based on deterioration clearly exceeding variability with no confounding factor explanation. Disappearance is always a major criterion. Marked amplitude reduction, acute threshold elevation or morphology simplification could be additional minor or moderate spinal cord monitoring criteria depending on the type of surgery and the program's technique and experience. Major criteria for supratentorial, brainstem or facial nerve monitoring include >50% amplitude reduction when warranted by sufficient preceding response stability. Future advances could modify these recommendations.

Posterior vertebral column resection in early onset spinal deformities

PURPOSE

Early onset spinal deformities (EOSD) can be life-threatening in very young children. In the growing spine, surgical intervention is often unavoidable and should be carried out as soon as possible. A deformed section of the spine not only affects the development of the remaining healthy spine, but also that of the chest wall (which influences pulmonary function), the extremities and body balance. Posterior vertebral column resection (PVCR) represents an effective surgical solution to address such problems. However, reports in the literature concerning PVCR are mostly limited to its use in adolescents or adults. The purpose of this study was to illustrate our experience with PVCR in EOSD and to describe the surgical technique with respect to the unique anatomy of young children.

MATERIALS AND METHODS

Four children [mean age 3.7 (range 2.5-5.2) years] with severe spinal deformity underwent PVCR through a single approach. Multimodal intraoperative monitoring was used in all cases. Surgery included one stage posterior circumferential resection of one vertebral body along with the adjoining intervertebral discs and removal of all posterior elements. A transpedicular screw-rod system was used for correction and stabilisation. Fusion was strictly limited to the resection site, allowing for later conversion into a growing rod construct at the remaining spine, if necessary. Relevant data were extracted retrospectively from patient charts and long spine radiographs.

RESULTS

The mean operation time was 500 (range 463-541) min, with an estimated blood loss of 762 (range 600-1,050) ml. Mean follow-up time was 6.3 (range 3.5-12.4) years. After PVCR, the mean Cobb angle for scoliosis was reduced from 69° (range 50-99°) to 29° (5-44°) and the sagittal curvature (kyphosis) from 126° (87-151°) to 61° (47-75°). The mean correction of scoliosis was 57 % (18-92°) and of kyphosis, 51 % (44-62°). There were no spinal cord-related complications. In three patients, spinal instrumentation for growth guidance (fusion less growing rod technique) was applied. Two patients had complications: one patient had a complication of anesthesia, halo pin failure, and revision surgery with extension of the instrumentation cranially due to loss of correction; the second patient had a postoperative infection, which required plastic reconstructive measures.

CONCLUSION

PVCR appears to be an effective technique to treat severe EOSD. There are important differences in its use in young children when compared with older patients. In patients with EOSD, additional surgical procedures are often necessary during growth, and hence non-fusion instrumentation beyond the vertebral resection site is advantageous, as it permits spinal growth and the later addition of fusion.

Intraoperative neurophysiologic monitoring during syringomyelia surgery: lessons from a series of 13 patients

BACKGROUND

Avoiding iatrogenic neurological injury during spinal cord surgery is crucially important. Intraoperative neurological monitoring (INM) has been widely used in a variety of spinal surgeries as a means of reducing the risk of intraoperative neurological insults. This study evaluates the benefits of INM specifically in spinal procedures for treatment of syringomyelia.

METHODS

Thirteen patients who underwent surgery for syrinx drainage with the assistance of INM were included in this study. In all patients both somatosensory-evoked potentials (SSEP) and motor-evoked potentials (MEP) were monitored. INM data and perioperative neurological evaluations were both recorded and analyzed.

RESULTS

Eleven patients underwent syringo-subarachnoid shunt (SSAS) surgery. One patient underwent syrinx drainage and foramen magnum decompression (FMD). One patient underwent syringo-pleural shunt (SPA) surgery. Baseline MEP and SSEP were recordable at the beginning of surgery in 11 patients (>84 %). In the other two cases, baseline data from specific INM modalities were absent, correlating with the antecedent neurologic symptomotology. Two patients exhibited significant intraoperative changes in MEP data that influenced the course of surgery and prompted removal or re-insertion of the shunt. Mild and transient worsening of preoperative symptoms was reported in these instances. No new postoperative neurological deficits were reported in the other 11 patients in whom INM data were preserved throughout surgery.

CONCLUSION

These data support routine use of INM in syringomyelia surgery. INM can alert the surgeon to potential intraoperative threats to the functional integrity of the spinal cord, providing a useful adjunct to spinal cord surgeries for the treatment of syringomyelia.

Usefulness of multi-channels in intraoperative spinal cord monitoring: multi-center study by the Monitoring Committee of the Japanese Society for Spine Surgery and Related Research

OBJECT

The purpose of this study is to analyze the data in terms of the number of channels employed to examine the usefulness of multi-channels in intraoperative spinal cord monitoring.

METHODS

The prerequisites for inclusion in the baseline data were as follows: (1) cases in which only CMAP monitoring was conducted; (2) cases in which monitoring was conducted under the same stimulation condition and the recording condition. Cases where inhalation anesthesia was used or muscle relaxants were used as maintenance anesthesia was excluded from the baseline data. Of the 6,887 cases, 884 cases met the criteria. The items examined for each of the different numbers of channels were the sensitivity and specificity, the false positive rate, the false negative rate, and the coverage rate of postoperative motor deficit muscles.

RESULT

To examine these two items in terms of the number of channels, the 4-channel group had lower sensitivity and specificity scores compared with the 8- and 16-channel groups (4 channels 73/93 %, 8 channels 100/97 %, 16 channels 100/95 %). Only four channels were derived for these cases and the coverage of postoperative motor deficit muscles was 38 % with only 30 out of the 80 postoperative motor deficit muscles in total being monitored. In the 8-channel group, it was 60 % with 12 of the 20 postoperative motor deficit muscles being monitored. The 16-channel group had 100 % coverage rate of postoperative motor deficit muscles.

CONCLUSION

We suggest that multi-channel monitoring of at least eight channels is desirable for intraoperative spinal cord monitoring.

Validity of somatosensory evoked potentials as early indicators of neural compromise in rat model of spinal cord compression

OBJECTIVE

To determine the percentage change in somatosensory evoked potential amplitude and the duration of spinal cord compression that can be tolerated intraoperatively in a rat model before there are significant post-operative functional deficits.

METHODS

Thirty two adult male Wistar rats were divided into four groups according to the percentage of induced SSEP signal loss; all animals had pre-operative functional testing. Following surgical placement of a balloon catheter in the thoracic sub-laminar space, SSEPs were recorded while the spinal cord was compressed by inflation of the balloon. The recordings were terminated after a different percentage loss of SSEP amplitude in each group. Functional behavioral testing was repeated after 24 h.

RESULTS

Only the group wherein the catheter was left inflated for 15 min after a complete (100%) loss of SSEP amplitude showed a significant deterioration in functional testing as compared to pre-operative baseline values. Functional testing remained normal for the groups in which termination of spinal cord compression occurred immediately after a decrease of SSEP amplitude to 50% or 100%.

CONCLUSIONS

SSEP loss of up to 100% can be tolerated in a rat model of spinal cord compression as long as the compression is terminated immediately after the SSEP decrease is detected. Prolonged spinal cord compression, with concomitant SSEP decrease, can result in post-operative functional deficits despite mitigating procedures to remove the compression.

SIGNIFICANCE

This study is an important first step in providing basic science evidence for the establishment of acceptable "alarm criteria" during spinal surgery.

Intraoperative decrease in amplitude of somatosensory-evoked potentials of the lower extremities with interbody fusion cage placement during lumbar fusion surgery

STUDY DESIGN

A retrospective analysis was performed.

OBJECTIVE

To characterize neurophysiological data of patients who had a decrease in amplitude of somatosensory-evoked potentials (SSEP) of the lower extremities secondary to interbody fusion cage placement during lumbar fusion surgery with no alert of the electromyography (EMG).

SUMMARY OF BACKGROUND DATA

The most consistently used and studied modalities of neurophysiological monitoring during spine surgery are SSEPs, motor-evoked potentials (MEPs), and EMG. In general, it is accepted that MEPs along with SSEPs are used to detect spinal cord injury and EMGs are used to detect nerve root injury.

METHODS

The medical records of a consecutive series of 115 patients who had undergone a transforaminal lumbar interbody fusion (TLIF) procedure in which SSEPs, MEPs, and EMGs were utilized for neurophysiological monitoring were retrospectively reviewed.

RESULTS

One hundred fifteen cases of TLIF procedures were reviewed. The follow-up was 2 years after the last procedure. A total of 5 cases that demonstrated intraoperative SSEP changes were found. The age range for these cases was from 39 to 81 years (mean age, 61 yr). All 5 patients developed SSEP changes that were secondary to interbody fusion cage placement. All 5 cases demonstrated reversal of the SSEP changes to baseline after removal of the interbody cage. Three of these cases had no new postoperative neurological findings. However, given that these 3 cases of SSEP change were associated with a surgical event that improved secondary to an intervention (in this case removal of the interbody cage), those cases were classified as presumed positive. Two of the 5 cases were in fact associated with a new postoperative neurological deficit.

CONCLUSION

To our knowledge this study demonstrates the first reported SSEP alerts that were associated with a posterior lumbar interbody cage placement without a corresponding EMG alert.

Use of multimodal intra-operative monitoring in averting nerve injury during complex hip surgery

Peripheral nerve injury is an uncommon but serious complication of hip surgery that can adversely affect the outcome. Several studies have described the use of electromyography and intra-operative sensory evoked potentials for early warning of nerve injury. We assessed the results of multimodal intra-operative monitoring during complex hip surgery. We retrospectively analysed data collected between 2001 and 2010 from 69 patients who underwent complex hip surgery by a single surgeon using multimodal intra-operative monitoring from a total pool of 7894 patients who underwent hip surgery during this period. In 24 (35%) procedures the surgeon was alerted to a possible lesion to the sciatic and/or femoral nerve. Alerts were observed most frequently during peri-acetabular osteotomy. The surgeon adapted his approach based on interpretation of the neurophysiological changes. From 69 monitored surgical procedures, there was only one true positive case of post-operative nerve injury. There were no false positives or false negatives, and the remaining 68 cases were all true negative. The sensitivity for predicting post-operative nerve injury was 100% and the specificity 100%. We conclude that it is possible and appropriate to use this method during complex hip surgery and it is effective for alerting the surgeon to the possibility of nerve injury.

Intraoperative monitoring in pediatric orthopedic spinal surgery: three hundred consecutive monitoring cases of which 10% of patients were younger than 4 years of age

STUDY DESIGN

Analysis of a prospective series of 300 consecutive cases undergoing intraoperative monitoring in pediatric orthopedic spinal surgery, of which 10% were children younger than 4 years.

OBJECTIVE

Determine feasibility and performance of intraoperative monitoring in children younger than 4 years. Analyze distinct physiopathologic mechanisms of relevant alerts.

SUMMARY OF BACKGROUND DATA

There are few studies in the literature concerning the intraoperative monitoring of children younger than 4 years. During childhood, the development of sensori-motor pathways is dominated by two coexisting phenomena, which have opposite effects: maturation decreasing latencies and height increasing them.

METHODS

We used intraoperative somatosensory-evoked potentials and neurogenic mixed evoked potentials with a flexible bipolar epidural electrode. Uniform total intravenous anesthesia was used.

RESULTS

Values of sensitivity and specificity of the monitoring showed slight differences between patients younger than 4 years versus older patients. There was no false-negative outcome. Various tendencies were highlighted. There were more true positive alerts for secondary etiologies than for idiopathic ones, for revision spinal surgeries than for index ones, and for boys than for girls. There were no more true positive alerts for children younger than 4 years than for older patients whereas the proportion of hemivertebrae was obviously greater for the younger group. Relevant monitoring alerts were more frequent in case of kyphoscoliosis. This is highlighted in case reports.

CONCLUSION

In some cases of kyphoscoliosis, during a posterior-based vertebral column resection, monitoring changes were corrected by positioning a rod that allowed correction of the position of the spine in the sagittal plane. Intraoperative spinal cord monitoring can be performed in children younger than 4 years and allows real-time assessment of spinal functional integrity.

Electromyographic monitoring and its anatomical implications in minimally invasive spine surgery

STUDY DESIGN

Literature review.

OBJECTIVE

The objective of this article is to examine current intraoperative electromyography (EMG) neurophysiologic monitoring methods and their application in minimally invasive techniques. We will also discuss the recent application of EMG and its anatomic implications to the minimally invasive lateral transpsoas approach to the spine.

SUMMARY OF BACKGROUND DATA

Minimally invasive techniques require that the same goals of surgery be achieved, with the hope of decreased morbidity to the patient. Unlike standard open procedures, direct visualization of the anatomy is decreased. To increase the safety of minimally invasive spine surgery, neurophysiological monitoring techniques have been developed.

METHODS

Review of the literature was performed using the National Center for Biotechnology Information databases using PUBMED/MEDLINE. All articles in the English language discussing the use of intraoperative EMG monitoring and minimally invasive spine surgery were reviewed. The role of EMG monitoring in special reference to the minimally invasive lateral transpsoas approach is also described.

RESULTS

In total, 76 articles were identified that discussed the role of neuromonitoring in spine surgery. The majority of articles on EMG and spine surgery discuss the use of intraoperative neurophysiological monitoring (IOM) for safe and accurate pedicle screw placement. In general, there is a paucity of literature that pertains to intraoperative EMG neuromonitoring and minimally invasive spine surgery. Recently, EMG has been used during minimally invasive lateral transpsoas approach to the lumbar spine for interbody fusion. The addition of EMG to the lateral approach has contributed to decrease the complication rate from 30% to less than 1%.

CONCLUSION

In minimally invasive approaches to the spine, the use of EMG IOM might provide additional safety, such as percutaneous pedicle screw placement, where visualization is limited compared with conventional open procedures. In addition to knowledge of the anatomy and image guidance, directional EMG IOM is crucial for safe passage through the psoas muscle during the minimally invasive lateral retroperitoneal approach.

Intraoperative electrophysiological monitoring in spine surgery

STUDY DESIGN

Review of the literature with analysis of pooled data.

OBJECTIVE

To assess common intraoperative neuromonitoring (IOM) changes that occur during the course of spinal surgery, potential causes of change, and determine appropriate responses. Further, there will be discussion of appropriate application of IOM, and medical legal aspects. The structured literature review will answer the following questions: What are the various IOM methods currently available for spinal surgery? What are the sensitivities and specificities of each modality for neural element injury? How are the changes in each modality best interpreted? What is the appropriate response to indicated changes? Recommendations will be made as to the interpretation and appropriate response to IOM changes.

SUMMARY OF BACKGROUND DATA

Total number of abstracts identified and reviewed was 187. Full review was performed on 18 articles.

METHODS

The MEDLINE database was queried using the search terms IOM, spinal surgery, SSEP, wake-up test, MEP, spontaneous and triggered electromyography alone and in various combinations. Abstracts were identified and reviewed. Individual case reports were excluded. Detailed information and data from appropriate articles were assessed and compiled.

RESULTS

Ability to achieve IOM baseline data varied from 70% to 98% for somatosensory-evoked potentials (SSEP) and 66% to 100% for motor-evoked potentials (MEP) in absence of neural axis abnormality. Multimodality intraoperative neuromonitoring (MIOM) provided false negatives in 0% to 0.79% of cases, whereas isolated SSEP monitoring alone provided false negative in 0.063% to 2.7% of cases. MIOM provided false positive warning in 0.6% to 1.38% of cases.

CONCLUSION

As spine surgery, and patient comorbidity, becomes increasingly complex, IOM permits more aggressive deformity correction and tumor resection. Combination of SSEP and MEP monitoring provides assessment of entire spinal cord functionality in real time. Spontaneous and triggered electromyography add assessment of nerve roots. The wake-up test can continue to serve as a supplement when needed. MIOM may prove useful in preservation of neurologic function where an alteration of approach is possible. IOM is a valuable tool for optimization of outcome in complex spinal surgery.

Intraoperative spinal cord and nerve root monitoring: a survey of Canadian spine surgeons

BACKGROUND

Intraoperative spinal cord and nerve root monitoring is used to identify an insult to the neural elements with the goal of preventing injury. There are 2 major categories of monitoring: evoked potentials (somatosensory evoked potentials and motor evoked potentials) and electromyography. The availability of intraoperative neuromonitoring and the indications for use vary widely. In this study, we aimed to document the current practices and opinions of Canadian spine surgeons with regards to intraoperative spinal monitoring.

METHODS

We surveyed members of the Canadian Spine Society about the availability and use of various types of intraoperative neuromonitoring modalities for surgical procedures.

RESULTS

We distributed 105 surveys and received 95 responses (90%). Somatosensory evoked potentials were the most commonly available form of intraoperative neuromonitoring, although it was available to only 65.3% of respondents. Surgeons in either full-time or part-time academic practice used monitoring more frequently than those in private practice (p < 0.001), but this association was not based on surgeon preference after controlling for availability. Years of practice and training background (orthopedic or neurosurgical) did not influence the use of monitoring. Canadian spine surgeons overwhelmingly reported that they use intraoperative neuromonitoring to reduce the risk of adverse operative events, rather than because of liability concerns. Most respondents believed that monitoring should be used in the correction of major deformity and scoliosis.

CONCLUSION

The availability of spinal monitoring in Canada is variable. Most surgeons believe that it is an important adjunct to improve patient safety.

Intraoperative neurophysiological monitoring during spine surgery: a review

Spinal surgery involves a wide spectrum of procedures during which the spinal cord, nerve roots, and key blood vessels are frequently placed at risk for injury. Neuromonitoring provides an opportunity to assess the functional integrity of susceptible neural elements during surgery. The methodology of obtaining and interpreting data from various neuromonitoring modalities-such as somatosensory evoked potentials, motor evoked potentials, spontaneous electromyography, and triggered electromyography-is reviewed in this report. Also discussed are the major benefits and limitations of each modality, as well as the strength of each alone and in combination with other modalities, with regard to its sensitivity, specificity, and overall value as a diagnostic tool. Finally, key clinical recommendations for the interpretation and step-wise decision-making process for intervention are discussed. Multimodality neuromonitoring relies on the strengths of different types of neurophysiological modalities to maximize the diagnostic efficacy in regard to sensitivity and specificity in the detection of impending neural injury. Thorough knowledge of the benefits and limitations of each modality helps in optimizing the diagnostic value of intraoperative monitoring during spinal procedures. As many spinal surgeries continue to evolve along a pathway of minimal invasiveness, it is quite likely that the value of neuromonitoring will only continue to become more prominent.

The use of physiological mapping and monitoring during surgery for ependymomas

INTRODUCTION

The use of intraoperative physiological monitoring has become increasingly common over the last decade and it is a useful tool to be employed for the resection of ependymomas of the central nervous system.

DISCUSSION

This manuscript reviews the history of its development and its methodology with a particular emphasis on those aspects of particular importance during surgery on ependymomas.

A survey of the "surgical and research" articles in the European Spine Journal, 2007

Over the last couple of years the European Spine Journal has become truly international with papers from all over the world, and at the same time it has increased its size. Professor Mulholland has selected and reviewed some 40 papers from over 200 published in 2007 and that he felt were of particular interest to practicing surgeons and would influence their management of patients, or papers that challenged established beliefs. Papers dealing with back pain, spondylolysis, tumors, spinal stenosis, spinal infection, clinical examination, lumbar disc herniation, spinal fractures, etc. are reviewed and their significance assessed. The aim of the review is to encourage readers to read the papers themselves, hopefully stimulated by the trenchant comments of the reviewer, both critical and laudatory.