Multimodality intraoperative monitoring during complex lumbosacral procedures: indications, techniques, and long-term follow-up review of 61 consecutive cases

Intraoperative Monitoring of the External Urethral Sphincter Reflex: A Novel Adjunct to Bulbocavernosus Reflex Neuromonitoring for Protecting the Sacral Neural Pathways Responsible for Urination, Defecation and Sexual Function

PURPOSE

Intraoperative bulbocavernosus reflex neuromonitoring has been utilized to protect bowel, bladder, and sexual function, providing a continuous functional assessment of the somatic sacral nervous system during surgeries where it is at risk. Bulbocavernosus reflex data may also provide additional functional insight, including an evaluation for spinal shock, distinguishing upper versus lower motor neuron injury (conus vs. cauda syndromes) and prognosis for postoperative bowel and bladder function. Continuous intraoperative bulbocavernosus reflex monitoring has been utilized to provide the surgeon with an ongoing functional assessment of the anatomical elements involved in the S2-S4 mediated reflex arc including the conus, cauda equina and pudendal nerves. Intraoperative bulbocavernosus reflex monitoring typically includes the electrical activation of the dorsal nerves of the genitals to initiate the afferent component of the reflex, followed by recording the resulting muscle response using needle electromyography recordings from the external anal sphincter.

METHODS

Herein we describe a complementary and novel technique that includes recording electromyography responses from the external urethral sphincter to monitor the external urethral sphincter reflex. Specialized foley catheters embedded with recording electrodes have recently become commercially available that provide the ability to perform intraoperative external urethral sphincter muscle recordings.

RESULTS

We describe technical details and the potential utility of incorporating external urethral sphincter reflex recordings into existing sacral neuromonitoring paradigms to provide redundant yet complementary data streams.

CONCLUSIONS

We present two illustrative neurosurgical oncology cases to demonstrate the utility of the external urethral sphincter reflex technique in the setting of the necessary surgical sacrifice of sacral nerve roots.

Intraoperative Neurophysiological Monitoring in Tethered Cord Syndrome Surgery: Predictive Values and Clinical Outcome

INTRODUCTION

"Tethered cord syndrome" (TCS) refers to a congenital abnormality associated with neurological signs and symptoms. The aim of surgery is to prevent or arrest their progression. This study reports a retrospective case series of tethered cord syndrome surgeries, supported by intraoperative neurophysiological monitoring.

METHODS

The case series comprises 50 surgeries for tethered cord syndrome in which multimodal intraoperative neurophysiological monitoring was performed using motor evoked potentials (transcranial motor evoked potentials [TcMEPs]), tibial nerve somatosensory evoked potentials (TNSEPs), and pudendal-anal reflex (PAR). The intraoperative neurophysiological monitoring results are reported and correlated with clinical outcomes.

RESULTS

Sensitivity, specificity, and negative predictive value were high for TcMEPs and TNSEPs, while PAR exhibited low sensitivity and positive predictive value but high specificity and negative predictive value. Fisher's exact test revealed a significant correlation between changes in TcMEPs, TNSEPs, and clinical outcome ( P < 0.000 and P = 0.049 respectively), but no correlation was detected between PAR and urinary/anal function ( P = 0.497).

CONCLUSIONS

While TcMEPs and TNSEPs were found to be reliable intraoperative neurophysiological monitoring parameters during tethered cord syndrome surgery, PAR had low sensitivity and positive predictive value probably because the reflex is not directly related to bladder function and because its multisynaptic pathway may be sensitive to anesthetics. New onset muscle weakness and sensory deficits were related to postoperative changes in TcMEPs and TNSEPs, whereas changes in PAR did not predict bladder/urinary impairment. Urinary deficits may be predicted and prevented with other neurophysiological techniques, such as the bladder-anal reflex.

Screw Stimulation Thresholds for Neuromonitoring in Minimally Invasive Oblique Lateral Lumbar Interbody Fusion (OLLIF): A Correlational Study

INTRODUCTION

This study presents findings from an investigation into the correlation of neuromonitoring techniques in minimally invasive lumbar fusions and their open counterparts regarding acceptable thresholds for screw stimulation. The threshold for acceptable stimulation value for open surgery has been established. The study compared acceptable thresholds for open pedicle screws where there is more connection between the screw and the soft tissue.

METHODS

The neuromonitoring data of 17 patients who underwent oblique lateral lumbar interbody fusion (OLLIF) procedures between September 2023 to May 2024 were reviewed. Neuromonitoring was conducted throughout surgeries, recording stimulation thresholds for pedicle screws insulated and uninsulated, to simulate the environment of a screw during open and minimally invasive surgery respectively. Patients' BMI was also collected for potential correlation analysis.

RESULTS

Results indicate a discernible correlation between stimulation thresholds in open and minimally invasive surgeries, but no definitive correlation with BMI due to sample size limitations. Though a significant correlation between the two stimulating styles is apparent, there is a good correlation to suggest what threshold should determine a standard stimulation threshold for minimally invasive surgeries.

CONCLUSION

The study emphasizes the need for refined neuromonitoring strategies in minimally invasive spinal fusion (MISF) surgeries to ensure patient safety and surgical effectiveness. Further research with larger cohorts is recommended to establish optimized protocols that have a clearly defined amplitude for MISF thresholds.

Intraoperative Neuromonitoring for Pediatric Pelvic Tumors

Background

Tumors of the pre-sacral and sacral spaces are a rare occurrence in children. Total tumor excision is required due to the significant risk of relapse in the event of partial surgery, but the surgical procedure may lead to postoperative problems such as urinary, sexual, and anorectal dysfunctions. Intraoperative neuromonitoring (IONM) has gained popularity in recent years as a strategy for preventing the onset of neurologic impairments by combining several neurophysiological techniques. The aim of our study is to describe the experience of Bambino Gesù Children's Hospital in the use of IONM in pediatric pelvic surgery.

Materials and Methods

The data of patients treated for pelvic malignancies at Bambino Gesù Children's Hospital from 2015 to 2019 were retrospectively collected. All patients were assessed from a neurologic and neuro-urologic point of view at different time-points (before and immediately after surgery, after 6 months, and 1-year follow-up). They were all monitored during a surgical procedure using multimodal IONM including transcranial motor evoked potentials (TcMEP), triggered-EMG (t-EMG), pudendal somatosensory evoked potentials (PSSEP), and bulbocavernosus reflex (BCR).

Results

During the study period, ten children underwent pelvic tumor removal at our Institution. In all cases, intraoperative neurophysiological recordings were stable and feasible. The preservation of neurophysiological response at the same intensity during surgical procedures correlated with no new deficits for all neurophysiological techniques.

Discussion

Although the impact of the IONM on surgical strategies and clinical follow-up is unknown, this preliminary experience suggests that the appropriate use of several neurophysiological techniques can influence both the radicality of pelvic tumor removal and the neurological and urological outcome at clinical follow-up. Finally, because of the highly complex anatomy and inter-individual variances, this is especially useful in this type of surgery.

Safety and efficacy of posterior vertebral column resection in complex pediatric deformities

Background

Vertebral column resection (VCR) is a well-known technique used for correction of complex spinal deformities. VCR could be done through a posterior only approach (Pvcr), or a combined anteroposterior approach, with almost comparable results. Early studies of Pvcr have reported high rates of complications, while subsequent studies have reported a reasonable complication rate. In this study, the authors represent and evaluate the initial results of using the Pvcr technique to correct complex pediatric deformities.

Objective

To evaluate the safety and efficacy of performing Pvcr to correct complex pediatric deformities.

Methods

Retrospective cohort study of data was collected from the database of pediatric deformity patients who were operated for correction of their deformities using posterior instrumentation and Pvcr at a single institution from 2015 to 2019.

Results

Twenty-one pediatric patients with a mean age 15.2 ± 3.5 years were enrolled in this study. The mean follow-up period was 26.3 ± 3.1 months. The mean Cobb angle has been decreased significantly from 82.9 ± 23.9 degrees to 28.8 ± 14.2 immediately after correction (correction rate 66.9 ± 10.8%, p < 0.001) with slight increase to 30.2 ± 14.9 after 24 months of follow-up (correction loss 4.3 ± 3.1%). The mean kyphotic angle has decreased significantly from 74.1 ± 15.9 to 25.4 ± 4.5 immediately after correction (correction rate 65.4 ± 2.9%, p < 0.001) with slight increase to 26.7 ± 5.2 after 24 months of follow-up (correction loss 4.8 ± 3.5%). The mean estimated blood loss was 2816.7 ± 1441.5 ml. The mean operative time was 339 ± 84.3 min. Self-image domain (part of SRS-22 questionnaire) has significantly improved from a mean preoperative of 2.3 ± 0.5 to a mean postoperative of 3.9 ± 0.4 after 24 months of correction (p < 0.001). As regards complications, chest tubes were inserted in 17 cases (81%), one case (4.8%) had suffered from deep wound infection and temporary respiratory failure, while 3 cases (14.3%) had neurological deficits.

Conclusion

Posterior vertebral column resection is considered a highly effective release procedure that aids in the correction of almost any type of complex pediatric deformities with a correction rate reaching 66.9 ± 10.8%. However, Pvcr is a challenging procedure with high estimated blood loss and risk of neurological deficits, so it must be done only by experienced spine surgeons in the presence of good anesthesia and neuromonitoring teams.

Mapping and monitoring of tethered cord and cauda equina surgeries

Surgery involving the cauda equina and tethered cord can be associated with significant functional disability including pain, motor and sensory deficits, as well as bladder, bowel, and sexual dysfunction. Neurophysiologic intraoperative monitoring and mapping during these surgeries using a variety of techniques and applications contributes to lessen the risk of permanent injury. This chapter reviews the anatomy of the pelvic floor, describes the techniques involved in monitoring and mapping this area, and describes the limitations of neurophysiology applications. Additionally, this chapter details mapping and monitoring techniques as they apply to tethered cord surgical release in both children and adults with review of outcome studies, and describes complications which can arise from tethered cord repair and injury to the cauda equina despite appropriate neurophysiologic intraoperative involvement.

Diagnostic Accuracy of SSEP Changes During Lumbar Spine Surgery for Predicting Postoperative Neurological Deficit: A Systematic Review and Meta-Analysis

STUDY DESIGN

This study is a meta-analysis of prospective and retrospective studies identified in PubMed, Web of Science, and Embase with outcomes of patients who received intraoperative somatosensory-evoked potential (SSEP) monitoring during lumbar spine surgery.

OBJECTIVE

The objective of this study is to determine the diagnostic accuracy of intraoperative lower extremity SSEP changes for predicting postoperative neurological deficit. As a secondary analysis, we evaluated three subtypes of intraoperative SSEP changes: reversible, irreversible, and total signal loss.

SUMMARY OF BACKGROUND DATA

Lumbar decompression and fusion surgery can treat lumbar spinal stenosis and spondylolisthesis but carry a risk for nerve root injury. Published neurophysiological monitoring guidelines provide no conclusive evidence for the clinical utility of intraoperative SSEP monitoring during lumbar spine surgery.

METHODS

A systematic review was conducted to identify studies with outcomes of patients who underwent lumbar spine surgeries with intraoperative SSEP monitoring. The sensitivity, specificity, and diagnostic odds ratio (DOR) were calculated and presented with forest plots and a summary receiver operating characteristic curve.

RESULTS

The study cohort consisted of 5607 patients. All significant intraoperative SSEP changes had a sensitivity of 44% and specificity of 97% with a DOR of 22.13 (95% CI, 11.30-43.34). Reversible and irreversible SSEP changes had sensitivities of 28% and 33% and specificities of 97% and 97%, respectively. The DORs for reversible and irreversible SSEP changes were 13.93 (95% CI, 4.60-40.44) and 57.84 (95% CI, 15.95-209.84), respectively. Total loss of SSEPs had a sensitivity of 9% and specificity of 99% with a DOR of 23.91 (95% CI, 7.18-79.65).

CONCLUSION

SSEP changes during lumbar spine surgery are highly specific but moderately sensitive for new postoperative neurological deficits. Patients who had postoperative neurological deficit were 22 times more likely to have exhibited intraoperative SSEP changes.Level of Evidence: 2.

Usefulness of external anal sphincter EMG recording for intraoperative neuromonitoring of the sacral roots-a prospective study in dorsal rhizotomy

BACKGROUND

In conus medullaris and cauda equina surgery, identification of the sacral nerve roots may be uncertain in spite of their anatomical/radiological landmarks. Mapping the sacral roots by recording the muscular responses to their stimulation may benefit from EMG recording of the External Anal sphincter (EAS) in addition to the main muscular groups of the lower limbs.

METHOD

In a consecutive series of 27 lumbosacral dorsal rhizotomy (DRh), authors carried out a prospective study on the reliability of the EMG recording of the EAS for identification of the S1 and S2 sacral roots.

RESULTS

An EAS-response was recorded in all the 27 (bilaterally) explored individuals, testifying good sensitivity and selectivity of the method. EAS-responses were obtained in 96.3% of the 54 stimulated sides of the S2 root versus in only 16.66% for the S1 root, so that an absence of response would indicate S1 rather than S2 level. Furthermore, comparison between myotomal distribution of the S1 and S2 roots showed a significant difference (p < 0.00001), so that myotomal profile may help to identify root level.

CONCLUSIONS

EMG recording of the EAS can be recommended for current intraoperative neuromonitoring. This simple method also provides-indirectly by extrapolation-information on the sacral motor pathways of the external urethral sphincter (EUS), as the later has the same somatic innervation via the pudendal nerve and related S2, S3, and S4 roots. Method can be helpful not only for DRh, of all varieties, but also for spine surgery, correction of dysraphisms, lipomas and/or tethered cord, and tumor resection.

Correlation between preoperative somatosensory evoked potentials and intraoperative neurophysiological monitoring in spinal cord tumors

Intraoperative neurophysiological monitoring (IONM) is widely used in spinal cord tumors (SCTs) removal surgery. This study mainly hypothesized that patients with prolonged latency of preoperative somatosensory evoked potentials (preSEP_Lat) would have more deteriorated intraoperative evoked potentials. Among 506 patients who underwent SCTs removal surgery, 74 underwent both preSEPs and IONM. The correlation between preSEP_Lat and intraoperative SEPs (ioSEPs) was mainly analyzed, and subgroup analysis according to anatomical type was also conducted. Secondly, whether preSEP_Lat related to intraoperative motor evoked potentials (ioMEPs) or postoperative motor deterioration (PMD) was analyzed. In addition, risk factors for PMD were examined among anatomical factors, including operation level, tumor-occupying area ratio, and anatomical type, as well as electrophysiological factors, such as preSEP_Lat, ioSEPs, and ioMEPs. Changes in ioSEP and ioMEP were considered significant even if they were recovered before the end of the monitoring. Patients with prolonged preSEP_Lat were more likely to have significant ioSEP changes for intradural-extramedullary (IDEM) but not for intramedullary or extradural tumors. The anatomical type and tumor-occupying area ratio were prognostic factors for transient PMD, while the ioSEPs were the only prognostic factor for persisted PMD over 4 weeks after surgery. PreSEPs are helpful in predicting the significant changes in ioSEPs during IDEM tumor removal surgery. The tumor-occupying area ratio and anatomical type are contributing factors for the transient PMD, whereas ioSEPs are prognostic factors in predicting the PMD that persists over 4 weeks after SCTs removal surgery. To our knowledge, this is the first study that mainly focused on the correlations of preoperative and intraoperative evoked potentials.

Neurophysiologic Intraoperative Monitoring for Spine Surgery: A Practical Guide From Past to Present

Intraoperative neuromonitoring was introduced in the second half of the 20th century with the goal of preventing patient morbidity for patients undergoing complex operations of the central and peripheral nervous system. Since its early use for scoliosis surgery, the growth and utilization of IOM techniques expanded dramatically over the past 50 years to include spinal tumor resection and evaluation of cerebral ischemia. The importance of IOM has been broadly acknowledged, and in 1989, the American Academy of Neurology (AAN) released a statement that the use of SSEPs should be standard-of-care during spine surgery. In 2012, both the AAN and the American Clinical Neurophysiology Society (ACNS) recommended that: "Intraoperative monitoring (IOM) using SSEPs and transcranial MEPs be established as an effective means of predicting an increased risk of adverse outcomes, such as paraparesis, paraplegia, and quadriplegia, in spinal surgery." With a multimodal approach that combines SSEPs, MEPs, and sEMG with tEMG and D waves, as appropriate, sensitivity and specificity can be maximized for the diagnosis of reversible insults to the spinal cord, nerve roots, and peripheral nerves. As with most patient safety efforts in the operating room, IOM requires contributions from and communication between a number of different teams. This comprehensive review of neuromonitoring techniques for surgery on the central and peripheral nervous system will highlight the technical, surgical and anesthesia factors required to optimize outcomes. In addition, this review will discuss important trouble shooting measures to be considered when managing ION changes concerning for potential injury.

Intraoperative Neurophysiology Monitoring for Spinal Dysraphism

Spinal dysraphism often causes neurological impairment from direct involvement of lesions or from cord tethering. The conus medullaris and lumbosacral roots are most vulnerable. Surgical intervention such as untethering surgery is indicated to minimize or prevent further neurological deficits. Because untethering surgery itself imposes risk of neural injury, intraoperative neurophysiological monitoring (IONM) is indicated to help surgeons to be guided during surgery and to improve functional outcome. Monitoring of electromyography (EMG), motor evoked potential, and bulbocavernosus reflex (BCR) is essential modalities in IONM for untethering. Sensory evoked potential can be also employed to further interpretation. In specific, free-running EMG and triggered EMG is of most utility to identify lumbosacral roots within the field of surgery and filum terminale or non-functioning cord can be also confirmed by absence of responses at higher intensity of stimulation. The sacral nervous system should be vigilantly monitored as pathophysiology of tethered cord syndrome affects the sacral function most and earliest. BCR monitoring can be readily applicable for sacral monitoring and has been shown to be useful for prediction of postoperative sacral dysfunction. Further research is guaranteed because current IONM methodology in spinal dysraphism is still deficient of quantitative and objective evaluation and fails to directly measure the sacral autonomic nervous system.

Secondary tethered cord syndrome in adult patients: retethering rates, long-term clinical outcome, and the effect of intraoperative neuromonitoring

BACKGROUND

The strategy for surgical treatment of tethered cord syndrome in pediatric patients is well established but still bares challenges for adult patients. This retrospective study was performed to assess the surgical outcome of adult patients with a secondary tethered cord syndrome and to evaluate the benefit of intraoperative neuromonitoring.

METHODS

Clinical charts of 32 consecutive adult patients who underwent in total 38 surgical untethering procedures at our facility between 2008 and 2018 were retrospectively analyzed. Epidemiological data, MRI scans, and postoperative results were evaluated.

RESULTS

The retethering rate in our patient cohort was 16%. Main complaints were maximal pain (82%), bladder dysfunction (79%), paresthesia (68%), and weakness in the lower extremities (68%). Forty-eight months after surgery, patients' symptoms generally improved, with an average level of pain of 19.1% (95% CI, 5.7-32.5%), paresthesia 28.7% (95% CI, 12.6-44.8%), weakness in the lower extremities 27.7% (95% CI, 11.1-44.4%), and bladder dysfunction 60.2% (95% CI, 41.6-78.7%). The use of neuromonitoring appears to have a positive impact on patient weakness (OR = 0.07; 95% CI, 0.01-0.68) and paresthesia (OR = 0.03; 95% CI, 0.00-2.18). This benefit is less clear for the retethering rate (OR = 0.45; 95% CI, 0.06-3.26) or the overall clinical outcome (OR = 0.70; 95% CI, 0.14-3.45). The presence of a preoperative Chiari syndrome, syringomyelia, or scoliosis had no relevant influence on the retethering rate.

CONCLUSIONS

Our data confirms that untethering surgery in adult patients is relatively safe and has a reasonable chance of clinical improvement of pain, paresthesia, and weakness in the lower extremities. The use of intraoperative monitoring has a positive influence on the improvement of preoperative paralysis.

Intraspinal dermoid and epidermoid cysts: Long-term outcome and risk factors

Objective: The literature on long-term outcome after resection of intraspinal dermoid and epidermoid tumors is limited. The purpose of this study was to review the progression-free survival (PFS), overall survival (OS), and long-term outcome in a consecutive series of 57 patients with intraspinal dermoid and epidermoid tumors. Design: Retrospective study. Methods: A total of 57 patients who underwent surgery at our institution between 2002 and 2010 were reviewed. Patients outcome were determined using the Japanese Orthopaedic Association score (JOA) and the McCormick score. Results: The follow-up data were 100% complete and the median follow-up time was 9.2 years. Gross total resection was performed in 21 patients (36.84%) and subtotal resection in 36 patients (63.16%). The PFS and OS at 8 years were 78.95% and 100% respectively. A good outcome was observed in 56.14% of patients based on the JOA and McCormick score. The univariate analysis showed that a tumor size of more than 4 cm, subtotal resection and sphincter disturbances were the influencing factors of poor outcome. Conclusion: The gold standard treatment for intraspinal tumors is gross total resection, but the operation needs to protect the remaining nerve function as much as possible and follow-up should be focused on patients with a high risk of poor outcome.

Radical excision of lumbosacral lipoma: an early experience of "followers"

BACKGROUND

Indication, timing, and method for surgical treatment of lumbosacral lipoma are controversial. Radical resection of the lumbosacral lipoma and complete reconstruction of the placode are supported in that better long-term outcome can be achieved without increasing complication rate compared with traditional surgical techniques.

OBJECTIVE

We analyzed the early surgical outcomes of lumbosacral lipoma treated with the untethering and radical excision of fat.

METHODS

Retrospective analysis of surgically treated 81 fresh lumbosacral lipoma cases with dorsal, transitional, and chaotic types and true lipomyelomeningocele (LMMC) was performed. Caudal and filar types were excluded.

RESULTS

Complete untethering was accomplished in 98%. Radical excision of the lipoma was attempted in all cases and achieved in 83%. Postoperative neurological complication was observed in 8 cases (10%). Group of lipoma types (dorsal + transitional vs. chaotic + true LMMC) and availability of radical lipoma excision turn out to be factors related to neurological outcomes in univariate analysis (p < 0.001 and p = 0.027, respectively). Group of lipoma types, availability of radical excision, and postoperative cord/dural sac (C/D) ratio are related factors in multivariate analysis (p = 0.025, p = 0.049, and p = 0.031).

CONCLUSIONS

As a follower of untethering and radical excision of fat, careful consideration is required to plan the surgery of lumbosacral lipoma on account of the "underestimated" complication rate. Type of the lipoma is the important factor determining the surgical outcome. Availability of complete radical excision and postoperative C/D ratio are the operative factors related to the neurological outcomes.

A method of untethering by skipping the area of positive responses on electrical stimulation during surgery of lumbosacral lipomatous malformation: 'hopping on a stepping stone'

OBJECTIVES

In complex lumbosacral lipomatous malformation or retethering, 'crotch' dissection, an incision on the dura or lipoma at the site lateral to the lipoma-cord fusion line saving underlying roots, is often not easy. Attempts of this dissection in complex and obscured conditions may cause damage to the spinal cord or nerve roots. A method for caudal extension of untethering while positive areas on electrical stimulation were encountered during crotch dissection of lumbosacral lipomatous malformation is described.

METHODS

After thinning out the negative-response area just caudal to the positive-response area, a small perforation is made at the negative-response area skipping the positive-response area with probing the dissection direction through the subarachnoid space by an inside out fashion. Subsequently, the procedure is continued caudally from the perforation site.

RESULTS

Safe caudal extension of untethering is possible using this method. Illustrative operative photographs are shown.

CONCLUSION

By using this method, safe untethering can be achieved avoiding root injuries in complicated lipomas such as chaotic or re-tethering cases.

Using subdural strip electrodes to define functional sensory nerves and the most inferior functional portion of the conus medullaris during detethering surgeries for tethered cord syndrome: a pilot study

OBJECTIVE

The aim of this study was to investigate the feasibility of using subdural strip electrodes, placed just rostral to the surgical field, to record sensory evoked potentials (SEPs) from the lumbosacral sensory nerves and define the most inferior functional portion of the conus medullaris during detethering surgery for spinal dysraphism and/or tethered cord syndrome (TCS).

METHODS

Six patients, 2 boys and 4 girls, aged 0.5 to 16 years, were enrolled in this study. One patient had lipomyelomeningocele-related, 4 had myelomeningocele-related, and 1 had diastematomyelia and lipomyelomeningocele-related TCS. In addition to the routine preparations that are needed for performing functional mapping and monitoring during surgery for spinal dysraphism and TCS, the patients had a 1 × 4 strip of electrodes placed rostral to the surgical field, where it was secured by a surgeon after opening the dura. With the patient under total intravenous anesthesia, the sensory nerves and conus medullaris were stimulated with a concentric bipolar electrode over the surgical field while SEPs were recorded with the strip electrodes to identify any possible sensory roots with remaining function and the most inferior functional portion of the conus medullaris.

RESULTS

The SEP amplitudes that were recorded with the subdural strip electrodes ranged from 4 to 400 μV, and the responses to sensory nerve stimulation were frequently much larger than were those to conus stimulation. Use of the SEP recordings for sensory mapping along with the routine mapping and monitoring techniques allowed detethering to be completed such that none of the patients sustained any new functional deficit after surgery.

CONCLUSIONS

Recording SEPs from the functional sensory nerves and conus medullaris through subdural strip electrodes proved to be a feasible and valuable tool during detethering surgery in young patients. This approach may help surgeons achieve maximal detethering while preserving important sensory functions, consequently retaining the patient's quality of life.

Aggressive Resection of Congenital Lumbosacral Lipomas in Adults: Indications, Techniques, and Outcomes in 122 Patients

OBJECTIVE

The authors reviewed the treatment of adult patients with congenital intraspinal lipomas with total/near-total resection and discussed their preoperative characteristics, prognostic factors, and surgical outcomes.

METHODS

Medical records of 122 adult patients with congenital lumbosacral lipomas undergoing total/near-total resection were systematically analyzed. The cohort was subdivided into 3 groups depending on symptom onset age: group 1 (≤5 years, n = 40), group 2 (>5 years but <18 years, n = 33), and group 3 (>18 years, n = 49). Preoperative and postoperative neurologic status were compared between groups and analyzed as a whole.

RESULTS

The most common symptom was bladder dysfunction (82.0%), followed by constipation (76.2%). At the 3-month follow-up, improvement was noted in most patients presenting with pain (87.2%) and neuropathic ulcers (70.0%). Overall, neurologic status was improved in 73.0% of patients and stabilized in 19.7% of patients. A binary logistic regression model identified shorter preoperative duration (P = 0.013) and preoperative pain (P = 0.005) as independent predictors of postoperative improvement. Neurosurgical complications developed in 16 patients, and wound complications occurred in 2 patients. Two of 3 patients who had recurred symptoms underwent repeated detethering surgery during long-term follow-up.

CONCLUSIONS

Despite longer preoperative duration than the pediatric population, adult patients with lumbosacral lipomas can still benefit from total/near-total resection especially regarding pain and foot ulcers, with low surgery-related morbidity. The long-term advantage of resecting additional lipoma in adults remains a point of discussion.

Retained medullary cord confirmed by intraoperative neurophysiological mapping

INTRODUCTION

A retained medullary cord (RMC) is a rare dysraphic malformation, recently described as a late arrest of secondary neurulation. RMC is also a severely tethering lesion. The critical role of intraoperative neurophysiology to safely manage a RMC has been only anecdotally reported.

CASE REPORT

We describe the case of a RMC in a 1.5-year-old child with Currarino syndrome. At surgery, an apparently normal-looking spinal cord, stretched and tethered by a lipoma to the level of S2-S3, was observed. The border between the functional conus and the non functional RMC was defined through neurophysiological mapping. The cord was sharply interrupted at this level and untethered. A specimen was sent for pathology, which confirmed the presence of glial and neural elements. The post-operative neurological exam was normal.

CONCLUSION

Neurosurgical procedure for RMC should only be rendered with intraoperative neurophysiological mapping, as the anatomical judgment would not suffice to allow a safe cutting of these "normal-looking" neural structures.

Saphenous nerve somatosensory evoked potentials: a novel technique to monitor the femoral nerve during transpsoas lumbar lateral interbody fusion

STUDY DESIGN

A retrospective analysis of a case series was performed.

OBJECTIVE

To describe a novel technique to monitor femoral nerve function by analyzing the saphenous nerve somatosensory evoked potential (SSEP) during transpsoas surgical exposures of the lumbar spine.

SUMMARY OF BACKGROUND DATA

During transpsoas direct lateral approaches to the lumbar spine, electromyography monitoring is frequently advocated; however, sensory and motor neurological complications are still being reported. Femoral nerve injury remains a feared complication at the L3-L4 and L4-L5 levels. The current neurophysiological monitoring modalities are not specific or sensitive enough to predict these injuries after the retractors are placed. The authors have developed a technique that is hypothesized to reduce femoral nerve injuries caused by retractor compression by adding saphenous nerve SSEPs to their neurophysiological monitoring paradigm.

METHODS

Institutional review board approval was granted for this study and the medical records along with the intraoperative monitoring reports from 41 consecutive transpsoas lateral interbody fusion procedures were analyzed. The presence or absence of intraoperative changes to the saphenous nerve SSEP was noted and the postoperative symptoms and physical examination findings were noted.

RESULTS

SSEP changes were noted in 5 of the 41 surgical procedures, with 3 of the patients waking up with a femoral nerve deficit. None of the patients with stable SSEP's developed sensory or motor deficits postoperatively. No patient in this series demonstrated intraoperative electromyography changes indicative of an intraoperative nerve injury.

CONCLUSION

Saphenous nerve SSEP monitoring may be a beneficial tool to detect femoral nerve injury related to transpsoas direct lateral approaches to the lumbar spine.

LEVEL OF EVIDENCE

4.

Intraoperative neurophysiology in tethered cord surgery: techniques and results

INTRODUCTION

Intraoperative neurophysiologic monitoring (IOM) is nowadays extensively used to minimize neurological morbidity in tethered cord surgery. Our goal is to describe and discuss the standard IOM techniques used during these surgical procedures and to summarize our clinical experience using a multimodal IOM approach.

MATERIAL AND METHODS

Neurophysiological mapping of the conus-cauda is performed through direct stimulation of these structures and bilateral recording from segmental target muscles. While mapping identifies ambiguous neural structures, their functional integrity during surgery can be assessed by monitoring techniques only, such as somatosensory evoked potentials (SEPs), transcranial motor-evoked potentials (MEPs) from the limb muscles and anal sphincters, and the bulbocavernosus reflex (BCR).

RESULTS

Between 2002 and 2012, we performed 48 surgical procedures in 47 patients with a tethered cord secondary to a variety of spinal dysraphisms. The monitorability rate was 84 % for SEPs, 97 % for limb muscle MEPs, 74 % for the anal sphincter MEPs, and 59 % for the BCR. In all patients but one, SEP, MEP, and BCR remained stable during surgery. Postoperatively, two out of 47 patients presented a significant-though transient-neurological worsening. In six patients, an unexpected muscle response was evoked by stimulating tissue macroscopically considered as not functional.

CONCLUSIONS

Mapping techniques allow identifying and sparing functional neural tissue and vice versa to cut nonfunctional structures that may contribute to cord tethering. Monitoring techniques, MEP and BCR in particular, improve the reliability of intraoperative neurophysiology, though these may require a higher degree of neuromonitoring expertise. IOM minimizes neurological morbidity in tethered cord surgery.

Detethering of a congenital tethered cord in adult patients: an outcome analysis

BACKGROUND

Tethered spinal cord syndrome (TCS) is characterized by attachment of the spinal cord down toward the tail end of the spine, comprising the danger of myelopathic symptoms. We retrospectively analyzed postoperative neurological outcome in adult patients with congenital TCS with special regard to the extent of resection of concomitant intraspinal lipomas.

METHODS

Medical records of 27 adult patients with congenital TCS (both with and without associated spinal lipomas) undergoing microsurgical detethering were systematically analyzed. Neurophysiological monitoring was available and feasible for all cases. Outcome parameters were preoperatively and postoperative neurological status; Wilcoxon rank test was used for statistical analysis.

RESULTS

In all patients, complete detethering was achieved. While urinary symptoms remained stable, all patients showed a non-significant tendency towards improvement of sensorimotor deficits. Both, patients with and without spinal lipoma experienced a significant postoperative amelioration of back pain. Patients with lipoma were found to suffer significantly less from radicular pain postoperatively (3/16). Furthermore, patients with a history of pain shorter than 1 year showed a significantly better chance for postoperative relief from back and radicular pain. The extent of lipoma resection had no significant impact on postoperative outcome.

CONCLUSIONS

Adult patients with symptomatic TCS profit from detethering, especially regarding relief of lower back and radicular pain. Complete removal of associated spinal lipomas does not seem to be mandatory for achieving a satisfying result.

Microsurgical treatment of spinal epidermoid and dermoid cysts in the lumbosacral region

The aim of this study was to evaluate the characteristics and surgical outcome of spinal epidermoid and dermoid cysts in the lumbosacral spine. We reviewed 26 patients with spinal epidermoid and dermoid cysts (15 epidermoid and 11 dermoid) treated between October 2000 and December 2010. The latter 15 patients of this series underwent neurophysiological monitoring during surgery. Gross total resection of the tumour was achieved in 46.2% of patients, and 53.8% underwent subtotal resection. In 14 patients, the tumour capsule adhered so tightly to the neural structures that a section of the capsule remained in situ. After surgery, the Japanese Orthopaedic Association score improved in 80.8% of patients, remained stable in 15.4%, and declined in 3.8%. The average follow-up period was 53 months. Three patients developed recurrence of the tumour and 20 patients resumed a normal working life. Microsurgical techniques and intraoperative neurophysiological monitoring are practical and reliable methods for radical removal of spinal epidermoid and dermoid cysts that involve the conus medullaris and cauda equina.

Complications associated with the treatment for spinal ependymomas

Spinal cord ependymomas are rare neoplasms, comprising approximately 5% of all CNS tumors and 15% of all spinal cord tumors. Although surgery was once reserved for diagnosis alone, the evolution of surgical practices has elevated resection to the treatment of choice for these lesions. While technological advances continue to improve the capacity for gross-total resections and thus decrease the risk of recurrence, ependymoma spinal surgery still contains a variety of potential complications. The presence of neurological deficits and deterioration are not uncommonly associated with spinal cord ependymoma surgery, including sensory loss, dorsal column dysfunction, dysesthetic syndrome, and bowel and bladder dysfunction, particularly in the immediate postoperative period. Surgical treatment may also lead to wound complications and CSF leaks, with increased risk when radiotherapy has been involved. Radiation therapy may also predispose patients to radiation myelopathy and ultimately result in neurological damage. Additionally, resections of spinal ependymomas have been associated with postoperative spinal instability and deformities, particularly in the pediatric population. Despite the advances in microsurgical techniques and intraoperative cord monitoring modalities, there remain a number of serious complications related to the treatment of spinal ependymoma tumors. Identification and acknowledgment of these potential problems may assist in their prevention, early detection, and increased quality of life for patients afflicted with this disease.

A role for motor and somatosensory evoked potentials during anterior cervical discectomy and fusion for patients without myelopathy: Analysis of 57 consecutive cases

BACKGROUND

Although the usage of combined motor and sensory intraoperative monitoring has been shown to improve the surgical outcome of patients with cervical myelopathy, the role of transcranial electric motor evoked potentials (tceMEP) used in conjunction with somatosensory evoked potentials (SSEP) in patients presenting with radiculopathy but without myelopathy has been less clear.

METHODS

We retrospectively reviewed all patients (n = 57) with radiculopathy but without myelopathy, undergoing anterior cervical decompression and fusion at a single institution over the past 3 years, who had intraoperative monitoring with both tceMEPs and SSEPs.

RESULTS

Fifty-seven (100%) patients presented with radiculopathy, 53 (93.0%) with mechanical neck pain, 35 (61.4%) with motor dysfunction, and 29 (50.9%) with sensory deficits. Intraoperatively, 3 (5.3%) patients experienced decreases in SSEP signal amplitudes and 4 (6.9%) had tceMEP signal changes. There were three instances where a change in neuromonitoring signal required intraoperative alteration of the surgical procedure: these were deemed clinically significant events/true positives. SSEP monitoring showed two false positives and two false negatives, whereas tceMEP monitoring only had one false positive and no false negatives. Thus, tceMEP monitoring exhibited higher sensitivity (33.3% vs. 100%), specificity (95.6% vs. 98.1%), positive predictive value (33.3% vs. 75.0%), negative predictive value (97.7% vs. 100%), and efficiency (91.7% vs. 98.2%) compared to SSEP monitoring alone.

CONCLUSIONS

Here, we present a retrospective series of 57 patients where tceMEP/SSEP monitoring likely prevented irreversible neurologic damage. Though further prospective studies are needed, there may be a role for combined tceMEP/SSEP monitoring for patients undergoing anterior cervical decompression without myelopathy.

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.

Validity and reliability of intraoperative monitoring in pediatric spinal deformity surgery: a 23-year experience of 3436 surgical cases

STUDY DESIGN

This was a 23-year retrospective study of 3436 consecutive pediatric orthopedic spinal surgery patients between 1995 and 2008.

OBJECTIVE

To demonstrate the effectiveness of multimodality electrophysiologic monitoring in reducing the incidence of iatrogenic neurologic deficit in a pediatric spinal surgery population.

SUMMARY OF BACKGROUND DATA

The elective nature of many pediatric spinal surgery procedures continues to drive the need for minimizing risk to each individual patient. Electrophysiologic monitoring has been proposed as an effective means of decreasing permanent neurologic injury in this population.

METHODS

A total of 3436 consecutive monitored pediatric spinal procedures at a single institution between January 1985 and September 2008 were reviewed. Monitoring included somatosensory-evoked potentials, descending neurogenic-evoked potentials, transcranial electric motor-evoked potentials, and various nerve root monitoring techniques. Patients were divided into 10 diagnostic categories. True-positive and false-negative monitoring outcomes were analyzed for each category. Neurologic deficits were classified as transient or permanent.

RESULTS

Seven of 10 diagnostic groups demonstrated true positive findings resulting in surgical intervention. Seventy-four (2.2%) potential neurologic deficits were identified in 3436 pediatric surgical cases. Seven patients (0.2%) had false-negative monitoring outcomes. These patients awoke with neurologic deficits undetected by neuromonitoring. Intervention reduced permanent neurologic deficits to 6 (0.17%) patients. Monitoring data were able to detect permanent neurologic status in 99.6% of this population. The ratio of intraoperative events to total monitored cases was 1 event every 42 surgical cases and 1 permanent neurologic deficit every 573 cases.

CONCLUSION

The combined use of somatosensory-evoked potentials, transcranial electric motor-evoked potentials, descending neurogenic-evoked potentials, and electromyography monitoring allowed accurate detection of permanent neurologic status in 99.6% of 3436 patients and reduced the total number of permanent neurologic injuries to 6.

Prognostic value of neurophysiologic intraoperative monitoring in tethered cord syndrome surgery

Neurophysiologic intraoperative monitoring is used in surgery for tethered cord syndrome. Our objective was to determine if neurophysiologic intraoperative monitoring is helpful in identifying which patients will have worsening symptoms after surgery. The spinal cord was stimulated before and after untethering until a motor response was obtained. The pre- and postoperative neurologic examination findings were noted. The motor response thresholds before and after untethering were compared using Student t tests. Forty patients were identified; 37 had higher motor response thresholds before untethering, whereas in three thresholds were higher after untethering. Of the 37 patients, two had worsening of motor function. All three patients with higher thresholds after untethering had worsening of motor function (P < 0.0001). An increase in the motor response threshold after surgical release of tethered cord syndrome indicates possible worsening of clinical symptoms. Spinal cord stimulation during tethered cord syndrome surgery may help predict neurologic outcome.

Prevention, identification, and treatment of perioperative spinal cord injury

OBJECT

In this report, the authors suggest evidence-based approaches to minimize the chance of perioperative spinal cord injury (POSCI) and optimize outcome in the event of a POSCI.

METHODS

A systematic review of the basic science and clinical literature is presented.

RESULTS

Authors of clinical studies have assessed intraoperative monitoring to minimize the chance of POSCI. Furthermore, preoperative factors and intraoperative issues that place patients at increased risk of POSCI have been identified, including developmental stenosis, ankylosing spondylitis, preexisting myelopathy, and severe deformity with spinal cord compromise. However, no studies have assessed methods to optimize outcomes specifically after POSCIs. There are a number of studies focussed on the pathophysiology of SCI and the minimization of secondary damage. These basic science and clinical studies are reviewed, and treatment options outlined in this article.

CONCLUSIONS

There are a number of treatment options, including maintenance of mean arterial blood pressure > 80 mm Hg, starting methylprednisolone treatment preoperatively, and multimodality monitoring to help prevent POSCI occurrence, minimize secondary damage, and potentially improve the clinical outcome of after a POSCI. Further prospective cohort studies are needed to delineate incidence rate, current practice patterns for preventing injury and minimizing the clinical consequences of POSCI, factors that may increase the risk of POSCI, and determinants of clinical outcome in the event of a POSCI.

Intradural microanatomy of the nerve roots S1–S5 at their origin from the conus medullaris

Object

The conus medullaris and the nerve roots from S-1 to S-5 regulate bladder function as well as movement and sensation of the lower extremities. This most caudal region of the spinal cord has not been studied in great detail anatomically despite its important regulatory role. The goal of this analysis is to characterize the normal intradural microanatomy of the sacral nerve roots at their origin from the conus medullaris.

Methods

The thecal sacs from 20 cadavers were fixated in formaldehyde and dissected under the operative microscope.

Results

More than 50 rootlets originated from the conus medullaris over a distance of < 3 cm. The rootlets were loosely organized into bundles by the arachnoid membrane with decreasing diameters. These diameters were 1.7 mm (ventral)/2.4 mm (dorsal) at S-1, and 0.17 mm (ventral)/0.4 mm (dorsal) at S-5. The roots were separated by neither the dentate ligament nor interradicular gaps. The number of rootlets decreased in the rostrocaudal direction with 2 ventral and 5 dorsal rootlets at S-1, but only 1 ventral (inconsistently found) and 2 dorsal rootlets at S-5. Typically, 1 nerve anastomosis was present between adjacent dorsal roots from S-1 to S-4. Nerve anastomoses between ventral roots or rootlets of the same root were less frequent. The dorsal segment of origin (linea radicularis) decreased in length from 7.2 mm at S-1 to 4.8 mm at S-5.

Conclusions

The current study provides anatomical details and specific morphometric data of the intradural contents at the level of the conus medullaris. This information is valuable for intraoperative orientation, endoscopic navigation, and possible intradural nerve stimulation.

The efficacy of motor evoked potentials in fixed sagittal imbalance deformity correction surgery

STUDY DESIGN

Retrospective analysis of transcranial motor evoked potential (TcMEP) responses and clinical outcome.

OBJECTIVE

To determine the sensitivity and specificity of TcMEPs to detect and predict isolated nerve root injury in selected patients having complex lumbar spine surgery.

SUMMARY OF BACKGROUND DATA

The surgical correction of fixed sagittal plane deformity involves posterior-based osteotomies and significant changes in the length of and space for the neural elements. The role of transcranial motor-evoked potential (TcMEP) monitoring in osteotomies below the conus has not been established. The purpose of this paper is to describe the relationship between neural complications from surgery and intraoperative TcMEP changes.

METHODS

We retrospectively studied 35 consecutive patients in a single center treated with posterior-based osteotomies for the correction of fixed sagittal plane deformity. Transcranial motor-evoked potentials, free-running and evoked electromyography data were assessed for each case. Analysis includes description of the intraoperative changes observed, and a correlation of changes with postoperative clinical findings.

RESULTS

Thirty-five consecutive patients underwent surgery for fixed sagittal plane deformity with complete neuromonitoring data. Twenty-five patients (71%) had an episode of greater than 80% reduction in MEP amplitude to at least 1 muscle. Fifteen of 25 had improvement of TcMEPs after repositioning of the legs (1), additional surgical decompression (4), or volume and pharmacologic resuscitation (10). All 15 of these awoke with no detectable neurologic injury. Ten patients (29%) had reduced TcMEP signals that did not improve despite further decompression and manipulation of the osteotomy site. All 10 had a greater than 67% drop in TcMEPs for at least 1 muscle persisting at the end of the case, and all had a postoperative neurologic deficit. The TcMEP changes in patients who demonstrated nerve injury postoperatively were observed most often during osteotomy closure or sustained dural retraction. 9 patients had weakness involving the iliopsoas or quadriceps; 1 patient had isolated unilateral dorsiflexion weakness. Monitoring TcMEPs in multiple muscle groups was both highly sensitive and specific for predicting injury. Nine patients had recovered motor function completely by discharge, and all but 1 patient (grade 4/5) had a normal motor examination at 6-week follow-up.

CONCLUSION

The use of TcMEPs is sensitive and specific to change in neural function. No patients had a false negative test. The rate of neural deficits is consistent with previous literature, suggesting that TcMEP monitoring may not prevent neural injury. However, there were several cases in which intraoperative intervention resulted in recovery of TcMEPs, and none of these patients sustained any postoperative neural deficit. The severity of neural deficits in this series was minor and the duration was limited. TcMEPs may contribute to calling attention to the need for intraoperative corrections including widening decompressions, improving perfusion, and limiting deformity correction so that more severe neural compromise may be prevented.

Predictive value of intraoperative neurophysiological monitoring during cervical spine surgery: a prospective analysis of 1055 consecutive patients

Object

Despite the growing use of multimodal intraoperative monitoring (IOM) in cervical spinal surgery, limited data exist regarding the sensitivity, specificity, and predictive values of such a technique in detecting new neurological deficits in this setting. The authors sought to define the incidence of significant intraoperative electrophysiological changes and new postoperative neurological deficits in a cohort of patients undergoing cervical surgery.

Methods

The authors conducted a prospective analysis of a consecutive series of patients who had undergone cervical surgery during a 5-year period at a university-based neurosurgical unit, in which multimodal IOM was recorded. Sensitivity, specificity, positive predictive values (PPVs), and negative predictive values (NPVs) were determined using standard Bayesian techniques. The study population included 1055 patients (614 male and 441 female) with a mean age of 55 years.

Results

The IOM modalities performed included somatosensory evoked potential (SSEP) recording in 1055 patients, motor evoked potential (MEP) recording in 26, and electromyography (EMG) in 427. Twenty-six patients (2.5%) had significant SSEP changes. Electromyographic activity was transient in 212 patients (49.6%), and 115 patients (26.9%) had sustained burst or train activity. New postoperative neurological deficits occurred in 34 patients (3.2%): 6 had combined sensory and motor deficits, 7 had new sensory deficits, 9 had increased motor weakness, and 12 had new root deficits. Of these 34 patients, 12 had spinal tumors, of which 7 were intramedullary. Overall, of the 34 new postoperative deficits, 21 completely resolved, 9 partially resolved, and 4 had no improvement. The deficits that completely resolved did so on average 3.3 months after surgery. Patients with deficits that did not fully resolve (partial or no improvement) were followed up for an average of 1.8 years after surgery.

Somatosensory evoked potentials had a sensitivity of 52%, a specificity of 100%, a PPV of 100%, and an NPV of 97%. Motor evoked potential sensitivity was 100%, specificity 96%, PPV 96%, and NPV 100%. Electromyography had a sensitivity of 46%, specificity of 73%, PPV of 3%, and an NPV of 97%.

Conclusions

Combined neurophysiological IOM with EMG and SSEP recording and the selective use of MEPs is helpful for predicting and possibly preventing neurological injury during cervical spine surgery.

Intraoperative neurophysiologic monitoring during spinal surgery

Intraoperative neurophysiologic monitoring (IONM) is a battery of neurophysiologic tests used to assess the functional integrity of the spinal cord, nerve roots, and other peripheral nervous system structures (eg, brachial plexus) during spinal surgery. The underlying principle of IONM is to identify emerging insult to nervous system structures, pathways, and/or related vascular supply and to provide feedback regarding correlative changes in neural function before development of irreversible neural injury. IONM data provide an opportunity for intervention to prevent or minimize postoperative neurologic deficit. Current multimodality monitoring techniques permit intraoperative assessment of the functional integrity of afferent dorsal sensory spinal cord tracts, efferent ventral spinal cord motor tracts, and nerve roots. Combined use of these techniques is useful during complex spinal surgery because these monitoring modalities provide important complementary information to the surgery team.

Electrophysiologic monitoring in neurosurgery

Electrophysiologic techniques have become common in the neurosurgical operating room. This article reviews the methods used for mapping neural structures or monitoring during surgery. Mapping methods allow identification of target structures for surgery, or for identifying structures to allow avoidance or plot safe pathways to deeper structures. Monitoring methods allow for surgery on nearby structures to warn of encroachment, thereby reducing unwanted injury.

A novel technique for the intraoperative monitoring of detrusor activity in intradural lesions of the cauda equina. Technical note

BACKGROUND

Intradural pathology in the region of the cauda equina is uncommon and generally comes to attention secondary to pain or neurologic deficit. A number of surgeons choose to excise these lesions under EMG monitoring of the nerve roots supplying the lower extremity muscles, anal sphincter, and detrusor muscle. In this article, the authors describe a detrusor muscle monitoring technique that has been found to be simple, reliable, and cost-effective in the management of intradural pathology of the cauda equina.

METHODS

Fourteen consecutive patients with tumors of the cauda equina who underwent surgical management performed using the standard Foley catheter monitoring technique were included in this study and their outcomes analyzed.

RESULTS

In 86% of patients, a gross total resection was achieved. Subtotal resections were performed in 2 patients because of involvement of critical nerve roots. In all cases, the nerve roots supplying the detrusor muscle were successfully identified using this technique. No patient suffered a clinically apparent decline in bladder function during the postoperative period.

CONCLUSION

The standard Foley catheter detrusor monitoring technique is a simple, reliable, and cost-effective method to identify and prevent injury to the sacral nerve roots innervating the urinary bladder during intradural exploration of the cauda equina.

Intraoperative mapping of sacral nervous system (S2-4)

Electrophysiological mapping of the sacral nervous system was used during operations on 80 patients with conus and cauda equina lesions. At surgery, under controlled muscle relaxation, the sacral neural elements (S2-4) were mapped using direct mono-polar stimulation and recording of compound muscle action potentials (CMAPs) from the external anal sphincter (EAS). Responses were obtained in 86.25% (69/80) of the patients. In 33 (82.5%) out of 40 patients with preoperative deficits involving the S2-4 segments, CMAPs could be elicited. Identification of nerve roots was useful in dissection of lipomyelomeningocoeles, tumour excisions and untethering of filum terminale. In three patients, stimulation of the filum terminale elicited motor responses and, hence, it was not sectioned. Intraoperative mapping of the S2-4 nerve roots under controlled muscle relaxation is feasible in a majority of patients, including those with deficits involving S2-4. This method was useful in sparing viable nerve roots during surgery in conus and cauda equina regions, and identification of 'functional' filum terminale.

Multimodality intraoperative neurophysiologic monitoring findings during surgery for adult tethered cord syndrome: analysis of a series of 44 patients with long-term follow-up

STUDY DESIGN

Prospective analysis of a consecutive series in which multimodality intraoperative neurophysiologic monitoring was used as an adjunct to microneurosurgery for adult tethered cord syndrome. The results of multimodality intraoperative neurophysiologic monitoring were compared with the "gold standard" (neurologic outcomes).

OBJECTIVE

To assess the sensitivity, specificity, and positive and negative predictive values of multimodality intraoperative neurophysiologic monitoring in surgery for adult tethered cord syndrome.

SUMMARY OF BACKGROUND DATA

Although intraoperative electrophysiologic techniques may help to minimize neural injury during spinal microneurosurgery, to our knowledge, no study has quantitatively evaluated the value of multimodality intraoperative neurophysiologic monitoring in the management of adult tethered cord syndrome.

METHODS

Multimodality intraoperative neurophysiologic monitoring included posterior tibial nerve somatosensory evoked potentials (SSEPs), continuous electromyographic (EMG) monitoring of the L2 to S4 myotomes, and evoked EMG. Follow-up neurologic evaluations were performed for at least 1 year.

RESULTS

A total of 44 consecutive patients, including 19 males and 25 females (aged 43 +/- 15 years), who underwent microsurgery for adult tethered cord syndrome were evaluated. After surgery, new neurologic deficits, including 1 transient and 1 permanent, developed in 2 patients. There was 1 patient who had persistent posterior tibial nerve SSEP amplitude reduction following microsurgical manipulation. In 1 patient, a transient posterior tibial nerve SSEP amplitude reduction prompted a change in microneurosurgical strategy. This patient awoke with no new postoperative neurologic deficits. For SSEPs, the sensitivity was 50% and specificity 100%. EMG bursts were recorded in 36 patients (82%). The 2 patients with postoperative neurologic worsening had EMG activity in the myotomes, where their new deficits presented. Continuous EMG had a sensitivity of 100% and a specificity of 19%.

CONCLUSIONS

To our knowledge, this is the largest series to date reporting the use of multimodality intraoperative neurophysiologic monitoring in the surgical management of adult tethered cord syndrome. Posterior tibial nerve SSEPs have high specificity, but low sensitivity, for predicting new neurologic deficits. In contrast, continuous EMG showed high sensitivity and low specificity. Evoked EMG accurately identified functional neural tissue. The combined recording of SSEPs in concert with continuous and evoked EMGs may provide a useful adjunct to complex microsurgery for adult tethered cord syndrome.

Surgical management of tethered cord syndrome in adults: indications, techniques, and long-term outcomes in 60 patients

OBJECT

The adult presentation of tethered cord syndrome (TCS) is well recognized but continues to pose significant diagnostic and management challenges. The authors performed a retrospective study of clinical outcomes after neurosurgical intervention in 60 adults with TCS.

METHODS

All patients who underwent detethering surgery for caudal cord tethering at Toronto Western Hospital between August 1993 and 2004 were identified. Their clinical charts, operative records, and follow-up data were reviewed. Detethering procedures were performed in 62 patients (age range 17-72 years) for TCS of various origins. Long-term (mean 41.5 months) follow-up data were obtained in 60 patients. The tethering lesions were tight terminal filum in 29 patients, postrepair myelomeningocele in 15, lipomyelomeningocele/lipoma in nine, split cord malformation in four, and arachnoidal adhesions in three. Fifty-nine patients presented with progressive pain and/or neurological dysfunction. One patient underwent prophylactic sectioning of the terminal filum. Most patients (71%) had bladder dysfunction at presentation. Microsurgical release of the tethered cord was performed in each case while using multimodality intraoperative neurophysiological monitoring. The most common complication was cerebrospinal fluid leakage, which occurred in nine patients and was managed by reinforcement sutures in four patients, temporary external drainage in three, and the placement of a lumboperitoneal shunt in two. Infective complications included superficial wound infection in three patients, meningitis in one, and urinary tract infection in one. One patient who had undergone multiple previous intradural procedures experienced worsened foot weakness postoperatively. Another patient experienced temporary unilateral lower-limb numbness. At follow up, improvement was noted in the majority of patients presenting with back (78%) and leg (83%) pain. Improvement was more likely in patients with preoperative motor weakness than in those with sensory deficits. Overall, neurological status was improved or stabilized in 90% of patients. Subjective improvement in bladder function was noted in 50% of patients with bladder dysfunction at presentation.

CONCLUSIONS

Surgery in adult patients with TCS is safe and effective for improving pain and neurological status in the majority of patients; however, patients who have undergone previous intradural detethering procedures in general fare less well, and considerable judgment is required in their management.

Intraoperative somatosensory evoked potentials to facilitate peripheral nerve release

PURPOSE

The significance of intraoperative somatosensory evoked potentials (SSEP) monitoring is well known during spinal surgery. This technology could be beneficial during peripheral nerve surgery as well. In order to illustrate potential applications, two cases of successful peripheral nerve release demonstrated by on-line, intraoperative, SSEP are reported. Clinical and technical features: The first case presents a complex brachial plexus lesion involving two mixed sensory-motor nerves: median and ulnar. The second case involved an entrapment neuropathy of the lateral femoral cutaneous nerve, a pure sensory nerve (meralgia paresthetica). For each patient we elicited specific peripheral nerve SSEP (recorded using bipolar cephalic montage) by stimulating each nerve independently. In each case, during difficult nerve dissection and after having excluded other possible factors of intraoperative SSEP variations, an increase of the SSEP amplitude was observed, and later correlated with favourable patient clinical outcome.

CONCLUSIONS

Two cases demonstrate that intraoperative SSEP monitoring may provide an effective tool to guide surgical dissection during peripheral nerve release. This technique has potentially beneficial clinical applications and warrants further investigation.

Multi-modality neurophysiological monitoring during surgery for adult tethered cord syndrome

During complex microneurosurgery performed in patients with tethered cord syndrome, the conus medullaris and the roots that innervate the lower limbs, bladder and bowel are potentially exposed to damage. The aim of multimodality intraoperative monitoring (IOM) is to reduce the risk of inadvertent injury of neural tissue. We simultaneously record tibial nerve somatosensory evoked potentials (SSEPs) from the scalp and free run electromyography (EMG) of limb muscles supplied by L2 to S2 roots, anal and urethral sphincters. We also identify critical neural structures in the operative field, including the conus and exiting nerve roots, with a nerve stimulator to evoke EMG. SSEPs assess the sensory pathways mainly mediated by the S1 roots. Continuous EMG provides the surgeon with immediate auditory feedback resulting from irritative discharges triggered by manipulation of nerve fibres. Microstimulation can distinguish the filum terminale, scar tissue and invasive tumors from functional neural tissue, thus minimizing the risk of iatrogenic injury. Overall multimodality IOM proves a valuable adjunct to microneurosurgery of the lumbosacral spine.