Intraoperative neurophysiology of the conus medullaris and cauda equina

The diagnostic accuracy of neuromonitoring for detecting postoperative bowel and bladder dysfunction in spinal oncology surgery: a case series

PURPOSE

Postoperative bowel and bladder dysfunction (BBD) poses a significant risk following surgery of the sacral spinal segments and sacral nerve roots, particularly in neuro-oncology cases. The need for more reliable neuromonitoring techniques to enhance the safety of spine surgery is evident.

METHODS

We conducted a case series comprising 60 procedures involving 56 patients, spanning from September 2022 to January 2024. We assessed the diagnostic accuracy of sacral reflexes (bulbocavernosus and external urethral sphincter reflexes) and compared them with transcranial motor evoked potentials (TCMEP) incorporating anal sphincter (AS) and external urethral sphincter (EUS) recordings, as well as spontaneous electromyography (s-EMG) with AS and EUS recordings.

RESULTS

Sacral reflexes demonstrated a specificity of 100% in predicting postoperative BBD, with a sensitivity of 73.33%. While sensitivity slightly decreased to 64.71% at the 1-month follow-up, it remained consistently high overall. TCMEP with AS/EUS recordings did not identify any instances of postoperative BBD, whereas s-EMG with AS/EUS recordings showed a sensitivity of 14.29% and a specificity of 97.14%.

CONCLUSION

Sacral reflex monitoring emerges as a robust adjunct to routine neuromonitoring, offering surgeons valuable predictive insights to potentially mitigate the occurrence of postoperative BBD.

The role of intraoperative neurophysiological monitoring in intramedullary spinal cord tumor surgery

Intramedullary tumors are a class of central nervous system tumors with an incidence of 2 to 4%. As they are located very deep and frequently cause postoperative neurological complications, surgical resection is difficult. In recent years, many surgeons have performed electrophysiological monitoring to effectively reduce the occurrence of postoperative neurological complications. Modern electrophysiological monitoring technology has advanced considerably, leading to the development of many monitoring methods, such as SSEPs, MEPs, DCM, and EMG, to monitor intramedullary tumors. However, electrophysiological monitoring in tumor resection is still being studied. In this article, we discussed the different monitoring methods and their role in monitoring intramedullary tumors by reviewing previous studies. Intratumorally tumors need to be monitored for a summary of the condition of the patient. Only by using various monitoring methods flexibly and through clear communication between surgeons and neurophysiological experts can good decisions be made during surgery and positive surgical results be achieved.

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.

Technical aspects of a new approach to intraoperative pelvic neuromonitoring during robotic rectal surgery

It has been found that rectal surgery still leads to high rates of postoperative urinary, fecal, or sexual dysfunction, which is why nerve-sparing surgery has gained increasing importance. To improve functional outcomes, techniques to preserve pelvic autonomic nerves by identifying anatomic landmarks and implementing intraoperative neuromonitoring methods have been investigated. The objective of this study was to transfer a new approach to intraoperative pelvic neuromonitoring based on bioimpedance measurement to a clinical setting. Thirty patients (16 male, 14 female) involved in a prospective clinical investigation (German Clinical Trials Register DRKS00017437, date of first registration 31/03/2020) underwent nerve-sparing rectal surgery using a new approach to intraoperative pelvic neuromonitoring based on direct nerve stimulation and impedance measurement on target organs. Clinical feasibility of the method was outlined in 93.3% of the cases. Smooth muscle contraction of the urinary bladder and/ or the rectum in response to direct stimulation of innervating functional nerves correlated with a change in tissue impedance compared with the pre-contraction state. The mean amplitude (Amax) of positive signal responses was Amax = 3.8%, negative signal responses from a control tissue portion with no stimulation-induced impedance change had an amplitude variation of 0.4% on average. The amplitudes of positive and negative signal responses differed significantly (statistical analysis using two-sided t-test), allowing the nerves to be identified and preserved. The results indicate a reliable identification of pelvic autonomic nerves during rectal surgery.

Surgery for spina bifida occulta: spinal lipoma and tethered spinal cord

The technical evolution of the surgery for spina bifida occulta (SBO) over the course of a half-century was reviewed with special foci placed on the spinal lipoma and tethered spinal cord. Looking back through history, SBO had been included in spina bifida (SB). Since the first surgery for spinal lipoma in the mid-nineteenth century, SBO has come to be recognized as an independent pathology in the early twentieth century. A half-century ago, the only option available for SB diagnosis was the plain X-ray, and pioneers of the time persevered in the field of surgery. The classification of spinal lipoma was first described in the early 1970s, and the concept of tethered spinal cord (TSC) was proposed in 1976. Surgical management of spinal lipoma with partial resection was the most widely practiced approach and was indicated only for symptomatic patients. After understanding TSC and tethered cord syndrome (TCS), more aggressive approaches became preferred. A PubMed search suggested that there was a dramatic increase of publications on the topic beginning around 1980. There have been immense academic achievements and technical evolutions since then. From the authors' viewpoint, landmark achievements in this field are listed as follows: (1) establishment of the concept of TSC and the understanding of TCS; (2) unraveling the process of secondary and junctional neurulation; (3) introduction of modern intraoperative neurophysiological mapping and monitoring (IONM) for surgery of spinal lipomas, especially the introduction of bulbocavernosus reflex (BCR) monitoring; (4) introduction of radical resection as a surgical technique; and (5) proposal of a new classification system of spinal lipomas based on embryonic stage. Understanding the embryonic background seems critical because different embryonic stages bring different clinical features and of course different spinal lipomas. Surgical indications and selection of surgical technique should be judged based on the background embryonic stage of the spinal lipoma. As time flows forward, technology continues to advance. Further accumulation of clinical experience and research will open the new horizon in the management of spinal lipomas and other SBO in the next half-century.

Intraoperative neurophysiology in pediatric neurosurgery: a historical perspective

INTRODUCTION

Intraoperative neurophysiology (ION) has been established over the past three decades as a valuable discipline to improve the safety of neurosurgical procedures with the main goal of reducing neurological morbidity. Neurosurgeons have substantially contributed to the development of this field not only by implementing the use and refinement of ION in the operating room but also by introducing novel techniques for both mapping and monitoring of neural pathways.

METHODS

This review provides a personal perspective on the evolution of ION in a variety of pediatric neurosurgical procedures: from brain tumor to brainstem surgery, from spinal cord tumor to tethered cord surgery.

RESULTS AND DISCUSSION

The contribution of pediatric neurosurgeons is highlighted showing how our discipline has played a crucial role in promoting ION at the turn of the century. Finally, a view on novel ION techniques and their potential implications for pediatric neurosurgery will provide insights into the future of ION, further supporting the view of a functional, rather than merely anatomical, approach to pediatric neurosurgery.

Is There a Role for Intraoperative Neuromonitoring in Intradural Extramedullary Spine Tumors? Results and Indications from an Institutional Series

While intraoperative neurophysiological monitoring (IONM) is considered a standard for intramedullary spinal cord tumor surgery, the effective role of IONM in intradural extramedullary (IDEM) tumors is still debated. We present the results of 60 patients affected by IDEM tumors undergoing surgery with the aid of IONM. Each patient was evaluated according to the modified McCormick scale (MMS) at admission, discharge and at follow-up. During surgery, motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) were studied using the Medtronic NIM-eclipse^® 32-channel system (Medtronic Xomed, Inc. 6743 Southpoint Drive North Jacksonville FL USA). Patients' age, gender and tumor location did not affect MMS modifications. Tumors involving more than three levels had an increased likelihood of MMS worsening, while meningioma pathology was associated with worse preoperative and 1-year follow-up MMS. No MEP amplitude ratio was able to predict clinical variations, while intraoperative SEP worsening was associated with 100% risk of poor MMS at discharge and with 50% risk of poor MMS at long-term follow-up. In our opinion, SEP monitoring is a valid tool that may contribute to the preservation of the patient's neurological status. MEP monitoring is not mandatory in IDEM surgery while more studies are required to explore the feasibility and the role of D-wave in this kind of surgery.

Updates on Intraoperative Neurophysiology During Surgery for Spinal Dysraphism

Spinal dysraphism is a group of disorders resulting from an embryologic failure of spinal cord development which can lead to a radicular-medullary mechanical stretch that generates vascular compromise and hypoxic-ischemic damage to the nervous structures of the conus-cauda region.Thus, the clinical relevance of the different types of spinal dysraphism is related to the possible neurologic deficits resulting from spinal cord tethering. The clinical presentation is heterogenous: from asymptomatic to very compromised patients. The indications and the time of a detethering surgery are still subject of debate, although there is an agreement on the high standards of treatment that have to be offered by the surgery. Intraoperative neurophysiology (ION) contributes to the safety of tethered cord surgery in reducing the risks of iatrogenic neurological damages.

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.

Safe Electromyography Stimulation Thresholds Within Kambin's Triangle During Endoscopic Transforaminal Lumbar Interbody Fusion

BACKGROUND

Transforaminal endoscopic approaches through Kambin's triangle traditionally require surgery to be performed without general anesthesia to allow live patient feedback. No reliable intraoperative neuromonitoring method specific to the dorsal root ganglion (DRG), the structure most at risk during this approach, currently exists.

OBJECTIVE

To correlate evoked electromyography (EMG) thresholds within Kambin's triangle with new postoperative pain or sensorimotor symptoms potentially resulting from DRG irritation.

METHODS

Data were prospectively collected for all patients undergoing endoscopic transforaminal lumbar interbody fusion (TLIF) under general anesthesia at a single institution. A stimulation probe was inserted into Kambin's triangle under fluoroscopic and robotic guidance, before passage of endoscopic instruments. EMG thresholds required to elicit corresponding myotomal responses were measured. Postoperatively, any potential manifestations of DRG irritation were recorded.

RESULTS

Twenty-four patients underwent a total of 34 transforaminal lumbar interbody fusion levels during the study period, with symptoms of potential DRG irritation occurring in 5. The incidence of new onset symptoms increased with lower stimulation thresholds. Sensitivities for EMG thresholds of ≤4, ≤8, and ≤11 mA were 0.6, 0.8, and 1, respectively. Corresponding specificities were 0.90, 0.69, and 0.55, respectively.

CONCLUSION

We demonstrated for the first time the feasibility of direct intraoperative neuromonitoring within Kambin's triangle in transforaminal endoscopic surgery. Eight milliampere seems to be a reasonable compromise between sensitivity and specificity for this monitoring technique. In the future, larger-scale studies are required to refine safe stimulation thresholds.

Monitoring spinal surgery for extramedullary tumors and fractures

Meningiomas are the most common intradural extramedullary tumors, followed by nerve sheath tumors that can also grow extradurally. Metastases are the most frequent extradural tumors and most commonly affect the thoracic vertebrae. Spinal fractures with column dislocation and/or instability require surgical fixation. Spine surgery for an extramedullary tumor or fracture usually involves decompression of neural elements and instrumentation for stabilization. These procedures risk spinal cord and nerve root injury. The incidence of nerve root deficits after resection of nerve sheath tumors is particularly high since the tumor grows from the rootlets. Intraoperative neurophysiologic monitoring and mapping techniques have been introduced to prevent iatrogenic neurologic deficits. These include motor and sensory evoked potentials, electromyography, compound muscle action potentials, and the bulbocavernosus reflex. The combination of techniques chosen for a particular procedure depends on the surgical level and the character of the lesion.

Bilobed intramedullary and extramedullary bronchogenic cyst of the conus medullaris: illustrative case

BACKGROUND

Spinal bronchogenic cysts are rare nonneoplastic congenital variants of neurenteric cysts. The natural history and surgical management of these lesions are poorly understood.

OBSERVATIONS

A 25-year-old male presented with progressive back pain and bilateral lower limb sciatica of 6 months’ duration. He had undergone subtotal resection of an intramedullary bronchogenic conus medullaris cyst 5 years prior. Magnetic resonance imaging revealed a recurrent bilobed intramedullary and extramedullary conus medullaris cystic lesion. The authors resected the lesion via a posterior approach with the aid of intraoperative neuromonitoring. Gross total resection was precluded by the tightly adherent nature of the cyst and the fact that stimulation of a residual intramedullary portion of the lesion evoked external anal sphincter responses.

LESSONS

This is the first reported case of a bilobed intramedullary and extramedullary bronchogenic cyst of the conus medullaris. This unique case lends insight into the poorly defined embryogenesis of bronchogenic cysts by favoring the split notochord syndrome theory rather than the ectopic ectoderm proposal. The importance of neuromonitoring when resecting these tightly adherent lesions is demonstrated. Finally, although the secretory nature of these lesions portends a tendency for cyst reaccumulation, it is imperative to recognize that this is usually a slow process.

Intraoperative Monitoring for Cauda Equina Tumors: Surgical Outcomes and Neurophysiological Data Accrued Over 10 Years

Objective

Cauda equina tumors affect the peripheral nervous system, and the validities of triggered electromyogram (tEMG) and intraoperative neurophysiologic monitoring (IOM) are unclear. We sought to evaluate the accuracy and relevance of tEMG combined with IOM during cauda equina tumor resection.

Methods

Between 2008 and 2018, an experienced surgeon performed cauda equina tumor resections using tEMG at a single institution. A cauda equina tumor was defined as an intradural-extramedullary or intradural-extradural tumor at the level of L2 or lower. The clinical presentation, extent of resection, pathology, recurrence, postoperative neurological outcomes, and intraoperative tEMG mapping and IOM data were retrospectively analyzed.

Results

One hundred three patients who underwent intraoperative tEMG were included; 38 underwent only tEMG (tEMG-only group), and 65 underwent a combination of tEMG and multimodal IOM (MIOM group). There were no significant differences between the neurologic outcomes, extents of resection, or recurrence rates of the 2 groups. No significant therapeutic benefit was observed; however, the accuracy of intraoperative predetection improved with the combination of IOM and tEMG (accuracy: tEMG-only group, 86.8%; MIOM group, 92.3%). When the involved rootlet was resected despite the positive tEMG result, motor function worsened in 3 of 8 cases. The sensitivity and specificity of tEMG were 37.5% and 94.7%, respectively.

Conclusion

tEMG is an essential adjunctive surgical tool for deciding on and planning for rootlet resection. If the tEMG finding is negative, complete resection, involving the rootlet, may be safe. The accuracy may be further improved by using a combination of tEMG and IOM.

Relationship between Preoperative Neuroradiological Findings and Intraoperative Bulbocavernosus Reflex Amplitude in Patients with Intradural Extramedullary Tumors

The current study aimed to evaluate the relationship between preoperative neuroradiological findings and intraoperative bulbocavernosus reflex (BCR) amplitude in patients with intradural extramedullary tumors. A total of 24 patients with lesions below the 12th thoracic vertebra were included in the analysis. Objective and subjective urinary symptoms were investigated using data obtained from medical records and the core lower urethral symptom score (CLSS) questionnaire. The lesion compression rate was evaluated with MRI. In the epiconus-to-conus medullaris (Epi-CM) group, BCR amplitude changes were found to be correlated with the compression rate (p <0.05). The preoperative CLSS of the group with a BCR amplitude of <50% was worse than that of the group with ≥50% (p <0.01). The group did not experience symptom improvement 6 months postoperatively based on the CLSS. The preoperative CLSS of the group with compression rate of ≥80% on imaging was worse than that of the group with <80% (p <0.05). In the group with preoperative compression rate of ≥80%, CLSS at 1 month and 6 months postoperatively was improved as compared to preoperative CLSS (p <0.01, p <0.05). Hence, BCR amplitude changes are associated with the degree of lesion compression on preoperative images and pre- and postoperative urinary symptoms. Patients with intradural extramedullary Epi-CM lesions with strong compression are likely to present with low BCR amplitude and worsened postoperative symptoms. It is considered that the risk of postoperative urinary symptoms increases even with careful surgical manipulation under these conditions.

Dynamic mapping using an electrified ultrasonic aspirator in lipomyelomeningocele and spinal cord detethering surgery-a feasibility study

BACKGROUND

Intraoperative neurophysiologic monitoring (IONM) is an established technique and adjunct of brain and spinal lesion resection surgery. In spina bifida syndrome surgery, mapping of the surgical wound is a common and accepted method in determining the position and functionality of nerve roots of the cauda equina (CE), especially when the anatomy is not straightforward and roots are splayed across or entangled within the lesion. Here, we describe a novel technique of continuous CE mapping using an electrified cavitron ultrasonic aspirator (eCUSA) in children with lipomyelomeningocele (LMMC) lesions.

METHODS

We assessed a method of dynamic CE mapping using an eCUSA as a stimulation probe. Twenty children (0.5-18 years) were included in this study, diagnosed with occult spina bifida LMMC in which the eCUSA stimulator was applied. IONM data and 2-weeks post-operative data were collected.

RESULTS

LMMC lesions were located in the lumbar, sacral, and lumbosacral spine. eCUSA stimulation at 0.3-3.0 mA intensities elicited positive lower extremity muscle responses in 12 of the 20 patients included in the study. These responses allowed the surgeon real-time identification of the nerve roots tangent at the LMMC-cauda equina structure and intensive removal of the fat tissue in the area non-responding to the eCUSA stimulation.

CONCLUSION

Continuous eCUSA-based stimulation of the cauda equina during LMMC resection is a feasible mapping technique with potential added value improving safety of untethering. Future studies evaluating extension of untethering, as well as the rates of retethering and long-term neurological and urological outcomes, are warranted.

Neurological deterioration as a result of improper neck position detected by intraoperative neurophysiological monitoring in a cervical stenosis patient: A case report

RATIONALE

Intraoperative neurophysiological monitoring (IONM) is widely used in spinal surgeries to prevent iatrogenic spinal cord injury (SCI). Most surgeons focus on avoiding neurological compromise intraoperatively, while ignoring the possibility of nerve damage preoperatively, such as neck positioning. Thus, this study aims to report a case with transient neurological deterioration due to improper neck position detected by IONM during cervical surgery.

PATIENT CONCERNS

A 63-year-old male patient had been suffering from hypoesthesia of the upper and lower extremities for three years.

DIAGNOSES

Severe cervical stenosis (C5-C7) and cervical ossification of a posterior longitudinal ligament.

INTERVENTIONS

The cervical stenosis patient underwent an anterior cervical corpectomy decompression and fusion (ACDF) surgery with the assistance of IONM. When the lesion segment was exposed, the SSEP and MEP suddenly elicited difficulty indicating that the patient may have developed SCI. All the technical causes of IONM events were eliminated, and the surgeon suspended operation immediately and suspected that the IONM alerts were caused by cervical SCI due to the improper position of the neck. Subsequently, the surgeon repositioned the neck of the patient by using a thinner shoulders pad.

OUTCOMES

At the end of the operation, the MEP and SSEP signals gradually returned to 75% and 80% of the baseline, respectively. Postoperatively, the muscle strength of bilateral biceps decreased from grade IV to grade III. Besides, the sensory disturbance of both upper extremities aggravated. However, the muscle power and hypoesthesia were significantly improved after three months of neurotrophic therapy and rehabilitation training, and no complications of nerve injury were found at the last follow-up visit.

LESSONS

IONM, consisting of SSEP and MEP, should be applied throughout ACDF surgery from the neck positioning to suture incisions. Besides, in the ward 1to 2 days before operation, it is necessary for conscious patients with severe cervical stenosis to simulate the intraoperative neck position. If the conscious patients present signs of nerve damage, they can adjust the neck position immediately until the neurological symptoms relieve. Therefore, intraoperatively, the unconscious patient can be placed in a neck position that was confirmed preoperatively to prevent SCI.

Efficacy of intraoperative bulbocavernosus reflex monitoring for the prediction of postoperative voiding function in adult patients with lumbosacral spinal tumor

Lumbosacral spinal tumor surgery is associated with a relatively high risk of postoperative voiding dysfunction. This study aimed to investigate the correlation between intraoperative bulbocavernosus reflex (BCR) changes and postoperative voiding function in adult patients with lumbosacral spinal tumors. We retrospectively reviewed 63 patients who underwent intradural conus and cauda equina tumor surgeries with intraoperative BCR monitoring. We evaluated patients' voiding functions for 6 months postoperatively. BCR was maintained in 60 patients and disappeared in 3 patients at the end of the surgery. Among the patients in whom BCR was maintained, examinations conducted at discharge and at 1- and 6-month follow-ups revealed that 7 (11.7%), 4 (6.7%), and zero (0.0%) patients experienced voiding difficulty, respectively. However, all 3 (100%) patients without BCR experienced voiding difficulty at the three corresponding follow-ups. Data analysis indicated no significant difference in voiding between the maintained and disappeared BCR groups 6-months postoperatively. The sensitivity, specificity, positive predictive, and negative predictive values of intraoperative BCR monitoring for detecting new and worsening difficulty in voiding were all 100% 6 months postoperatively. Our results shows that intraoperative BCR monitoring is a reliable predictor of voiding function following surgery in adult patients undergoing lumbosacral spinal tumor surgery. Intraoperative BCR monitoring can be useful for assessing and monitoring the integrity of the voiding function during lumbosacral spinal tumor surgery.

Early de-tethering: analysis of urological and clinical consequences in a series of 40 children

PURPOSE

Early de-tethering procedures are performed on spinal dysraphisms to prevent neuro-urological deterioration caused by growth. Partial lipoma removal may cause delayed deterioration by re-tethering, while complete removal may increase the risk of postoperative worsening. The present study evaluates the risk of postoperative deterioration and the protective potential of intraoperative neurophysiological monitoring (IOM), with a special reference to the conus lipomas treated with the radical approach.

METHODS

Forty toddlers (< 24 months) underwent complete perioperative neurological and urological assessment, including urodynamic study (UDS). The dysraphisms were subgrouped according to Pang's classification. IOM was applied in all patients: transcranial motor evoked potentials (tMep) combined with mapping were recorded in all cases while bulbocavernosus reflex (BCR) was evaluable just in 7 cases.

RESULTS

At preoperative evaluation, 11 children already had UDS impairment and 2 had motor disturbances before neurosurgery. At 1-month follow-up, preoperative motor disturbances were stable, 7/11 UDS alterations normalized, and the remaining 4 were stable. At 6-month follow-up, all motor deficits and 8/11 preoperative UDS alterations had improved. Unfortunately, 7 children with previously normal UDS experienced a new impairment after surgery: 2/7 normalized while 5/7 did not recover. This postoperative permanent urodynamic impairment occurred in 4 chaotic lipoma (CLchaos) and in one terminal myelocystocele (TMC) that means a surgical deterioration rate of 22% for the high risk cases.

CONCLUSIONS

This small highly selected series confirms that early de-tethering may stop or revert the spontaneous neuro-urological deterioration: in fact, preoperative UDS impairment was frequent (27.5%) and improved in all the low surgical risk cases (limited dorsal myeloschisis, filar, transitional and dorsal lipomas). On the contrary, in CLchaos and TMC, early de-tethering was unable to revert preoperative UDS impairment, and radical surgery carried a high risk of new neuro-urological deterioration directly caused by the operation. In our experience, IOM had a protective role for motor functions, while it was less effective for the neuro-urological ones, probably due to the anesthesiology regimens applied. In conclusion, among the dysraphisms, CLchoas proved to be the worst enemy that often camouflages at MRI. Affording it without all possible IOM weapons carries a high risk to harm the patient.

Filum terminale lipomas-the role of intraoperative neuromonitoring

BACKGROUND

Filum terminale lipomas (FTL) represent a sub-type of spinal lipomas, where there is fatty infiltration of the filum. It becomes a surgical entity when it manifests as clinical or radiological tethered cord syndrome. Intraoperative neuromonitoring (IONM) has been suggested as a valuable tool in children for tethered cord surgeries. FTL is distinct and cannot be compared with complex tethered cord syndrome (TCS). Untethering an FTL is a relatively straightforward microsurgical exercise, usually based on anatomical findings. Neurological morbidity in FTL untethering is extremely low. The necessity of IONM in FTL has not been evaluated. The objective of this study was to identify the role of IONM in untethering an FTL METHODS: Available electronic data and case files were interrogated to identify children (0-18 years) who underwent an untethering of FTL between 2008 and 2019. We had a shift in our policy and tried to use IONM as often as possible in all tethered cord surgery from 2014. All children were categorised under 'IONM implemented' or 'no IONM' group. Outcomes analysed were as follows: (1) Clinical status on short-term and long-term follow-up, (2) alteration of surgical course by IONM and (3) complications specifically associated with IONM RESULTS: Among 80 children included in this study, IONM was implemented in 37 children and 43 children underwent untethering without IONM. 32.5% of children were 'syndromic'. Seventy-five percent of children were under age 3 years during surgery. Both groups (No IONM vs. IONM implemented) were well matched in most variables. Majority of 'no IONM' surgeries were performed prior to 2014. There was no neurological morbidity in the entire cohort. Mean duration of follow-up was 49.10 (± 33.67) months. Short-term and long-term clinical status remained stable in both cohorts. In 16 children, the filum was stimulated. Based on our protocol, majority had a negative response. One child showed a positive response, contradicted by thorough microscopic inspection. Despite a positive response, the filum was untethered. IONM was not associated with any complication in this study.

CONCLUSION

FTL untethering is an inherently low-risk microsurgery in experienced hands with rarely reported neurological morbidity. IONM may not be required for all FTL and may be used more judiciously.

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.

Double neurophysiological certification of the filum terminale during sectioning surgery in pediatric population

Background:

Surgery of thickened-fibrolipoma filum terminale (FT) is performed routinely and without conflict but is not a risk-free surgical procedure. Intraoperative neurophysiological monitoring with mapping techniques can help to certify the FT before sectioning. However, a tailored surgical approach to cauda equina and a low threshold of surrounding nerve roots can confuse the final surgical decision. The aim is to demonstrate the usefulness of this double methodology for FT certification.

Methods:

A prospective study collected and reviewed retrospectively, from 2015 to 2018, 40 patients undergoing an FT surgery section were included in the study. After opening the dura mater and under the microscope, the cauda equina mapping is performed and the recording of muscles of the lower limbs and the external anal sphincter. In addition, a high-intensity stimulation of constant current of an isolated FT for a short period of time and in a dry surgical field, obtaining a bilateral-polyradicular-symmetrical response of cauda equina nerve roots.

Results:

Traditional motor mapping identified FT in 65% (26/40) of patients. Although, 35% (14/40) of the patients still have low-intensity stimuli response (<1 mA) of a muscle, especially anal sphincter. When this happens, the optimization of the dissection around FT is performed. After that, 25% (10/40) of the patients still having a muscle response in spite of seem isolated FT. Increasing the stimulation intensity up to 20 mA evoked a cauda equina response in all cases. No postoperative neurological impairment was observed in this series.

Conclusion:

This proposed methodology accurately confirms the FT so that it can be safely found and cut. The Double Neurophysiological Certification improves the gap of the traditional mapping techniques of cauda equina and can be used in a variety of more complex surgeries in this area.

Selective dorsal rhizotomy: functional anatomy of the conus-cauda and essentials of intraoperative neurophysiology

INTRODUCTION

Spasticity is the result of an exaggeration of the monosynaptic muscle stretch reflex due to lesions affecting the central nervous system, in particular an upper motor neuron lesion. Selective dorsal rhizotomy (SDR) is a surgical technique developed to treat spastic diplegia, one of the common forms of cerebral palsy, resulting from the lack of supraspinal inhibitory controls. The aim of SDR is to identify and cut a critical amount of the sensory rootlets, in particular those contributing the most to spasticity, in order to relieve the patient from lower limb spasticity while preserving motor strength and sphincter control. Various surgical techniques to perform SDR have been proposed over time. Similarly, intraoperative neurophysiology (ION)-first introduced by Fasano and colleagues in 1976-is a safe and effective tool to guide the surgeon in the procedure of SDR, but different ION strategies are used by different authors, and the value of ION itself has been questioned.

METHODS

The purpose of this paper is to review the anatomo-physiological background of SDR, the historical development of the surgical technique, and the essential principles of ION.

RESULTS

While some surgeons privilege a single-level approach and others a multi-level approach, nowadays, there are still neither agreement nor guidelines on the percentage of roots to be cut. Rather, a tailored approach based on both the preoperative functional status as well as intraoperative ION findings seems reasonable. ION is considered not essential to decide the percentage of roots to cut, but it assists to distinguish between ventral and dorsal roots, and to preserve sphincterial function, whenever S2 rootlets are included in SDR.

CONCLUSIONS

To optimize the balance between reduction of spasticity and preservation of motor strength while minimizing the neurological damage remains the main goal of SDR.

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.

Bulbocavernosus Reflex Monitoring During Intramedullary Conus Tumor Surgery

A T10 to L2 spinal cord tumor exploration and biopsy was performed with intraoperative neurophysiological monitoring (IONM) on a 75-year-old male diagnosed with an intradural intramedullary appearing spinal cord lesion with no other lesions in the central nervous system, chest, abdomen or pelvis.

Intraoperative neurophysiology consisted of transcranial electrical motor evoked potentials (TCeMEPs), somatosensory evoked potentials (SSEPs), triggered and spontaneous electromyography (S-EMG, T-EMG), bulbocavernosus reflex (BCR) and train of four (TOF) monitoring. Loss of BCR responses during conus exposure and identification were resolved with multiple small pauses in manipulation throughout the procedure. T-EMG mapping aided in identification and avoiding the removal of nervous tissue.

Postoperatively the patient experienced some mild weakness in his left foot and leg that correlated with a significant amplitude drop in the left abductor hallucis TCeMEP. By the following day, the patient was almost back to preoperative baseline. The patient’s bowel and bladder function were preserved, consistent with final BCR recordings. The patient was discharged to rehabilitation postoperatively. Pathology results indicated glioblastoma.

This case study demonstrates the utility of a multimodality approach with bulbocavernosus reflex and urethral sphincter monitoring to optimize intraoperative data to the surgeon during conus tumor surgeries.

Muscle responses to radicular stimulation during lumbo-sacral dorsal rhizotomy for spastic diplegia: Insights to myotome innervation

OBJECTIVE

Most of knowledge on muscle radicular innervation was from explorations in root/spinal cord pathologies. Direct and individual access to each of the lumbar-sacral -ventral and dorsal- nerve roots during dorsal rhizotomy for spastic diplegia allows precise study of the corresponding muscle innervation. Authors report the lumbo-sacral segmental myotomal organization obtained from recordings of muscle responses to root stimulation in a 20-children prospective series.

METHODS

Seven key-muscles in each lower limb and anal sphincter were Electromyography (EMG)-recorded and clinically observed by physiotherapist during L2-to-S2 dorsal rhizotomy. Ventral roots (VR), for topographical mapping, and dorsal roots (DR), for segmental excitability testing, were stimulated, just above threshold for eliciting muscular response.

RESULTS

In 70% of the muscles studied, VR innervation was pluri-radicular, from 2-to-4 roots, with 1 or 2 roots being dominant at each level. Overlapping was important. Muscle responses to DR stimulation were 1.75 times more extended compared to VR stimulation. Inter-individual variability was important.

CONCLUSIONS

Accuracy of root identification and stimulation with the used method brings some more precise information to radicular functional anatomy.

SIGNIFICANCE

Those neurophysiological findings plead for performing Intra-Operative Neuromonitoring when dealing with surgery in the lumbar-sacral roots.

Feasibility and effectiveness of a newly modified protocol-guided selective dorsal rhizotomy via single-level approach to treat spastic hemiplegia in pediatric cases with cerebral palsy

PURPOSE

It still remains challenging to treat CP cases with spastic hemiplegia using SDR via a single-level approach when guided by the traditional EMG response grading system. Our aim was to assess the feasibility and effectiveness of a newly modified protocol-guided single-level laminectomy SDR to treat such pediatric patients.

METHODS

A retrospective cohort review was conducted in the CP cases with spastic hemiplegia undergone our newly modified protocol-guided single-level approach SDR since May 2016 to October 2017, and followed by intensive rehabilitation program for at least 12 months in both Shanghai Children's Hospital and Shanghai Rehabilitation and Vocational Training Center for the Disabled. Inclusion and exclusion criteria were set for the selection of patients in the current study. Our study focused on the setup, EMG recording interpretation, and outcome measures for this newly modified rhizotomy scheme.

RESULTS

Eleven cases were included in the current study. Based on our new rhizotomy protocol, a total of 34 rootlets over our 11 cases were cut (2 in 4, 3 in 4, 4 in 1, and 5 rootlets in 2 cases, respectively). After SDR and the following rehabilitation program at a mean duration of 19 months, muscle tone of those "target muscles" in affected lower extremities which identified during pre-op assessment decreased by a mean of 1.4 degrees (Modified Ashworth Scale) in our cases. Strength of those target muscles and ROM of joints involved in their lower limbs were reported to have improved significantly as well. All cases showed major progress with regard to their motor function. A mean of about 10-point increase of GMFM-66 score was reported, and five of six cases who were with GMFCS level II preoperatively improved their GMFCS level at the last assessment. Kinematics of joints of hip, knee, and ankle on the affected side in our cases demonstrated a major correction, along with improvement of their foot pressure patterns to the ground during their gait cycles. Surgery-related complications, such as cerebral-spinal fluid leak/infection, long-term hypoesthesia, or urinary/bowel incontinence were not recorded in the current study.

CONCLUSION

Single-level SDR when guided by our simplified rhizotomy protocol is feasible and effective to treat pediatric CP cases with spastic hemiplegia.

Selective dorsal rhizotomy in cerebral palsy spasticity - a newly established operative technique in Slovenia: A case report and review of literature

BACKGROUND

Spasticity affects a large number of children, mainly in the setting of cerebral palsy, however, only a few paediatric neurosurgeons deal with this problem. This is mainly due to the fact that until 1979, when Fasano has published the first series of selective dorsal rhizotomy (SDR), neurosurgeons were able to provide such children only a modest help. The therapy of spasticity has made a great progress since then. Today, peroral drugs, intramuscular and intrathecal medicines are available, that may limit the effects of the disease. In addition, surgical treatment is gaining importance, appearing in the form of deep brain stimulation, peripheral nerve procedures and SDR. All these options offer the affected children good opportunities of improving the quality of life.

CASE SUMMARY

A 15-year old boy is presented that was surgically treated for spasticity as a result of cerebral palsy. Laminotomy at L1 level was performed and L1 to S1 nerve roots were isolated and divided in smaller fascicles. Then, the SDR was made.

CONCLUSION

We describe a patient report and surgical technique of SDR that was performed in Slovenia for the first time.

Multimodal intraoperative monitoring during surgical correction of scoliosis to avoid neurologic damage

The purpose of this study was to evaluate the application of multimodal intraoperative monitoring (MIOM) system in patients with congenital scoliosis (CS) and adolescent idiopathic scoliosis (AIS).Twelve patients who underwent posterior surgical correction of scoliosis for CS and AIS from June 2014 to July 2018 were enrolled in this study. During the operation, we monitored the functional status of the spinal cord by MIOM. An abnormal somatosensory evoked potential was defined as a prolonged latency of more than 10% or a peak-to-peak amplitude decline of more than 50% when compared to baseline. An abnormal transcranial motor evoked potential (TcMEP) was defined as a TcMEP amplitude decrease of more than 50%. A normal triggered electromyography response, which presented with the absence of an electrical response on stimulation at 8.2 mA, indicated that the pedicle screw was not in contact with the spinal cord or nerve root.A total of 12 patients underwent MIOM surgery, of which 9 patients with negative MIOM had no significant deterioration of neurological function postoperatively, and exhibited satisfactory surgical correction of scoliosis during follow-ups. However, the remaining 3 patients suffered from MIOM events, 2 patients had normal neurological function, and 1 patient had deteriorated neurological function postoperatively.Using MIOM in CS and AIS surgery could promptly detect iatrogenic neurological injury at the early stage. Therefore, rapid response by appropriate intraoperative interventions can be taken to minimize the injury. Besides, stable MIOM recordings encourage surgeons to correct scoliosis even when the Cobb angle of scoliosis was extremely large.

Decreased MEPs during subcutaneous dissection for untethering surgery of a "true" lipomyelomeningocele: aggravated traction of the spinal cord by release of the sac from the original nest

PURPOSE

It is well known that the preoperative enlarged sac in occult spinal dysraphism, in which the spinal cord is attached to its dome, can be associated with neurological deficits by aggravation of spinal cord traction. We experienced a similar phenomenon during the early stage of untethering surgery for "lipomyelomeningocele in a strict sense (LMMC)."

CLINICAL PRESENTATION

We report a case of a 3-month-old girl with LMMC, which showed decreased motor evoked potentials (MEPs) in the lower extremities during the early stage of untethering surgery. The sac was released from the original nest by incision with separation of the overlying skin and dissection from the muscle fascia. The sac became rounder, and the spinal cord attached to the dome of the sac was further stretched. After aspiration of cerebrospinal fluid from the sac, the MEPs recovered. Postoperatively, the patient had no neurological deficits.

CONCLUSIONS

Although this phenomenon rarely occurs, release of the herniated sac of LMMC from the original nest during the early stage of untethering surgery may result in neurological changes. Application of intraoperative neurophysiological monitoring helps to detect electrophysiological deterioration and can prevent neurological deficits.

Diagnostic and therapeutic values of intraoperative electrophysiological neuromonitoring during resection of intradural extramedullary spinal tumors: a single-center retrospective cohort and meta-analysis

OBJECTIVE

With the advent of intraoperative electrophysiological neuromonitoring (IONM), surgical outcomes of various neurosurgical pathologies, such as brain tumors and spinal deformities, have improved. However, its diagnostic and therapeutic value in resecting intradural extramedullary (ID-EM) spinal tumors has not been well documented in the literature. The objective of this study was to summarize the clinical results of IONM in patients with ID-EM spinal tumors.

METHODS

A retrospective patient database review identified 103 patients with ID-EM spinal tumors who underwent tumor resection with IONM (motor evoked potentials, somatosensory evoked potentials, and free-running electromyography) from January 2010 to December 2015. Patients were classified as those without any new neurological deficits at the 6-month follow-up (group A; n = 86) and those with new deficits (group B; n = 17). Baseline characteristics, clinical outcomes, and IONM findings were collected and statistically analyzed. In addition, a meta-analysis in compliance with the PRISMA guidelines was performed to estimate the overall pooled diagnostic accuracy of IONM in ID-EM spinal tumor resection.

RESULTS

No intergroup differences were discovered between the groups regarding baseline characteristics and operative data. In multivariate analysis, significant IONM changes (p < 0.001) and tumor location (thoracic vs others, p = 0.018) were associated with new neurological deficits at the 6-month follow-up. In predicting these changes, IONM yielded a sensitivity of 82.4% (14/17), specificity of 90.7% (78/86), positive predictive value (PPV) of 63.6% (14/22), negative predictive value (NPV) of 96.3% (78/81), and area under the curve (AUC) of 0.893. The diagnostic value slightly decreased in patients with schwannomas (AUC = 0.875) and thoracic tumors (AUC = 0.842). Among 81 patients who did not demonstrate significant IONM changes at the end of surgery, 19 patients (23.5%) exhibited temporary intraoperative exacerbation of IONM signals, which were recovered by interruption of surgical maneuvers; none of these patients developed new neurological deficits postoperatively. Including the present study, 5 articles encompassing 323 patients were eligible for this meta-analysis, and the overall pooled diagnostic value of IONM was a sensitivity of 77.9%, a specificity of 91.1%, PPV of 56.7%, and NPV of 95.7%.

CONCLUSIONS

IONM for the resection of ID-EM spinal tumors is a reasonable modality to predict new postoperative neurological deficits at the 6-month follow-up. Future prospective studies are warranted to further elucidate its diagnostic and therapeutic utility.

Intraoperative neurophysiological monitoring of the bulbocavernosus reflex during surgery for conus spinal lipoma: what are the warning criteria?

OBJECTIVE

Despite the surge in the intraoperative use of the bulbocavernosus reflex (BCR) during lumbosacral surgeries, there are as yet no widely accepted BCR warning criteria for use with intraoperative neurophysiological monitoring (IONM). The author's aim was to find clinically acceptable warning criteria for use in IONM of the BCR.

METHODS

Records of IONM of the BCR in 164 operations in 163 patients (median age 5 months) with a conus spinal lipoma who underwent surgery between August 2002 and May 2016 were retrospectively analyzed. The outcomes of IONM of the BCR were grouped by the residual amplitude at the end of surgery: group 1, ≥ 50%; group 2, 25%-50% (including the lower bound, but not the upper); and group 3, < 25%. Cases in which the BCR was lost were separately assessed as a subgroup of group 3. The postoperative urinary complication rate was used to verify the warning criteria zones.

RESULTS

The BCR could be monitored in 149 surgeries (90.9%). There were 118 surgeries (79.2%) in group 1, 18 (12.1%) in group 2, and 13 (8.7%) in group 3. Two surgeries (11.1%) in group 2 and 6 (46.2%) in group 3 resulted in urinary complications. In the group 3 subgroup (lost BCR), all 5 surgeries resulted in urinary complications. The cutoff value of the BCR amplitude reduction was placed between groups 1 and 2 (zone 1: cutoff 50%), groups 2 and 3 (zone 2: cutoff 25%), and group 3 and its subgroup (zone 3: cutoff zero, present or lost). In zone 1, the positive predictive value (PPV) was 25.8% and the negative predictive value (NPV) was 100%. In zone 2, the PPV was 53.8% and the NPV 98.5%. In zone 3, the PPV was 100% and the NPV 97.9%. The PPV was highest in zone 3. The NPV was highest in zone 1, but its PPV was low (25.8%).

CONCLUSIONS

The "lost or remained" criterion of BCR amplitude (zone 3: cutoff zero) can be used as a predictor of postoperative urinary function. As a warning criterion, the cutoff value of the BCR amplitude reduction at 75% (zone 2) may be used. This preliminary clinical report on the warning criteria for the BCR may contribute to improving the safety of surgery for conus spinal lipoma.

Efficacy of Anal Needle Electrodes for Intraoperative Spinal Cord Monitoring with Transcranial Muscle Action Potentials

Study Design

Retrospective study.

Purpose

To examine the relationship between postoperative bowel bladder disorder (BBD) and the efficacy of needle electrodes for the external anal sphincter (EAS) in intraoperative spinal cord monitoring with transcranial muscle action potentials (Tc-MsEP).

Overview of Literature

Spinal surgery for spina bifida, spinal cord tumor, and spinal tethered cord syndrome has a high rate of postoperative BBD. Monitoring of the EAS with Tc-MsEP is frequently performed during spinal surgery. We initially used plug-surface electrodes for this purpose, but have more recently switched to needle electrodes for the monitoring of the EAS. To date, there has been no comparison between the utility of these electrodes.

Methods

Waveform derivation, exacerbation of postoperative BBD, and sensitivity and specificity for prediction of BBD by 70% amplitude reduction of EAS activity using needle and plug-surface electrodes were investigated in 239 spine surgeries. The cut-off for the % drop in amplitude for BBD prediction was determined for EAS monitoring using a needle electrode.

Results

The overall rate of postoperative BBD aggravation was 7.1% (17/239 cases), with the individual rates using needle and plug-surface electrodes being 6.9% (8/116) and 7.3% (9/123), respectively. The waveform derivation rate was significantly higher using needle electrodes (91.3% [106/116] vs. 76.4% [94/123], p <0.01). In patients with baseline waveform detection, the sensitivity and specificity for postoperative BBD were similar in the two groups. With needle electrodes, a cutoff amplitude of Tc-MsEP for the EAS at the end of surgery of 25% of the baseline amplitude had a sensitivity of 89% and specificity of 82% for the prediction of postoperative BBD aggravation.

Conclusions

The significantly higher waveform derivation rate using needle electrodes suggests that these electrodes are effective for monitoring the EAS in spinal surgery in cases with preoperative BBD.

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.

Multimodal intraoperative monitoring during reduction of spine burst fracture and dislocation prevents neurologic injury

This study aims to evaluate the application of multimodal intraoperative monitoring (MIOM) in surgical treatment for spine burst fracture and dislocation (SBFD) patients.Eleven patients who underwent posterior reduction and instrumentation (PRI) for SBFD from June 2014 to July 2016 were included into the study. The function of the spinal cord was monitored by MIOM. The muscle strength of the lower extremities and American Spinal Injury Association (ASIA) scores were, respectively, evaluated (before surgery, and at 1, 3, 6, and 12 months after surgery). Furthermore, the extent of reduction was also assessed.Muscle strength recovery, ASIA score changes, and the extent of reduction were correlated with MIOM results. Among the 11 patients who received surgery under MIOM, 8 patients with negative MIOM results during the operation did not demonstrate neurological deterioration postoperatively and exhibited improvements in ASIA scores during follow-ups. However, among the 3 patients who encountered MIOM events (case 4, 7, and 8), 2 patients avoided nerve lesion and 1 patient suffered from neurologic deterioration postoperatively.The application of MIOM technology during PRI surgery may detect spinal cord impairment at the early stage, and operative schemes can be modified before permanent nerve compromise is triggered by surgical manipulation.

Prevention and prediction of postoperative bowel bladder disorder using an anal plug electrode with Tc-MsEP monitoring during spine surgery

A retrospective study was performed to examine the efficacy of intraoperative monitoring of the external anal sphincter (EAS) muscle-evoked potential after a transcranial muscle-action potential (Tc-MsEP) in spinal cord surgery, and to evaluate alarm points for EAS waveform deterioration related to postoperative bowel bladder disorder (BBD). BBD is caused by damage to the hypogastric, pelvic, and pudendal nerves and leads to a significant reduction in quality of life. Intraoperative Tc-MsEP monitoring using the EAS is common to prevent neurological deficit, but the relationship of BBD with intraoperative monitoring of the EAS has not been examined. Waveform derivation from the EAS using a plug-type surface electrode was investigated in 123 spine surgeries in which Tc-MsEP was recorded intraoperatively outside the anal sphincter. An acceptable baseline waveform from the EAS was detected in 105 of the 123 cases (85.3%). Preoperative BBD was present in 16 cases, postoperative BBD occurred in 8 cases, and intraoperative waveform deterioration from the EAS was detected in 25 cases. The derivation rate was significantly lower in cases with preoperative BBD compared to those without BBD (62.5% vs. 88.9%, p<0.01). Waveform deterioration from the EAS had a sensitivity of 100%, specificity of 93.0%, positive predictive value of 50%, and negative predictive value of 100% for detection of postoperative BBD. All postoperative BBD was detected with an EAS amplitude decrease to <30% of baseline. Therefore, in spine surgery, a Tc-MsEP intraoperative EAS amplitude decrease to <30% of the control waveform may be useful for prediction of postoperative BBD.

Intraoperative neurophysiological mapping and monitoring in spinal tumor surgery: sirens or indispensable tools?

Spinal tumor (ST) surgery carries the risk of new neurological deficits in the postoperative period. Intraoperative neurophysiological monitoring and mapping (IONM) represents an effective method of identifying and monitoring in real time the functional integrity of both the spinal cord (SC) and the nerve roots (NRs). Despite consensus favoring the use of IONM in ST surgery, in this era of evidence-based medicine, there is still a need to demonstrate the effective role of IONM in ST surgery in achieving an oncological cure, optimizing patient safety, and considering medicolegal aspects. Thus, neurosurgeons are asked to establish which techniques are considered indispensable. In the present study, the authors focused on the rationale for and the accuracy (sensitivity, specificity, and positive and negative predictive values) of IONM in ST surgery in light of more recent evidence in the literature, with specific emphasis on the role of IONM in reducing the incidence of postoperative neurological deficits. This review confirms the role of IONM as a useful tool in the workup for ST surgery. Individual monitoring and mapping techniques are clearly not sufficient to account for the complex function of the SC and NRs. Conversely, multimodal IONM is highly sensitive and specific for anticipating neurological injury during ST surgery and represents an important tool for preserving neuronal structures and achieving an optimal postoperative functional outcome.

Long-term evaluation of intraoperative neurophysiological monitoring-assisted tethered cord surgery

PURPOSE

Patients with tethered spinal cord have been investigated for short-term effects after tethered spinal cord surgery in the past. However, little is known about the long-term effects in this patient group. In this retrospective, longitudinal, observational study, a patient sample of a previous report of 65 patients was reassessed to observe the long-term effects of intraoperative neurophysiological monitoring-assisted tethered cord surgery.

METHODS

With the use of patient charts and a survey, patients were scored on four domains: (1) neurological deficits, (2) urological deficits, (3) pain symptoms, and (4) orthopedic deficits. Measurements were performed at four moments in time: (1) preoperatively, (2) postoperatively, (3) follow-up 1 (4.6 years), and (4) follow-up 2 (11.2 years). Besides this, a subgroup analysis and a quality of life questionnaire were performed.

RESULTS

When observing the symptom domains in the long-term, the pain domain appeared to improve most postoperatively after which it remained stable over time. The neurological and urological domains showed a stable, slightly decreasing trend in the long-term follow-up. The orthopedic domain showed a significant increase of the number of patients with scoliosis during the long-term follow-up.

CONCLUSIONS

Lasting effects of stability in the neurological, urological, and pain domains were observed. Close monitoring during follow-up might contribute to early recognition of progressive scoliosis, in spite of detethering, in a risk group defined by females who underwent tethered cord surgery at or under the age of 12 years old with either lipomyelomeningocele, split cord malformation, or myelomeningocele. Detethering does not appear to protect these patients against progressive scoliosis.

Below the belt: sensory mapping and monitoring in the sacral-pudendal region

Originally described in 1982, scalp somatosensory evoked potential responses can be recorded after stimulation of multiple different pudendal nerve- and sacral root-supplied structures. The resulting P40 response is usually the highest amplitude at Cz. Responses are generally easy to resolve and therefore should be of equivalent ease to follow for neurophysiologic intraoperative monitoring versus lower limb peripheral nerve somatosensory evoked potentials (e.g., tibial or fibular [peroneal] nerves), but sizeable reports of pudendal somatosensory evoked potential monitoring are few. Direct orthodromic sensory nerve action potential recording from the cauda equina in response to single such sacral stimuli has been reported of utility for preserving roots that participate in urinary control during dorsal rhizotomy procedures for spasticity. Technical application of both techniques is quite straightforward. As in most areas of neurophysiologic intraoperative monitoring, there are no well-constructed historical control series informing use of these techniques and, certainly, no clinical trials. Given the socially devastating consequences of urinary and anal continence disturbances and a fairly high rate of functional postoperative disturbances when sacral roots are manipulated, this field begs more active clinical investigation.

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.

Improvement in intraoperative transcranial electrical motor-evoked potentials in tethered cord surgery: an analysis of 45 cases

BACKGROUND

Improvement of transcranial electrical motor-evoked potentials (TeMEPs) following untethering during tethered cord surgery (TCS) and its clinical significance have not been analyzed in the literature.

METHODS

Forty-five consecutive cases of tethered cord were operated on with multimodality intraoperative neurophysiological monitoring (IONM) between February 2005 and January 2012. Intraoperative TeMEP change was classified as improvement, worsening or no change. Motor, sensory, bladder and bowel symptoms and signs were evaluated preoperatively, in the first week post-surgery and at the last follow-up (maximum of 2 years).

RESULTS

Patient age ranged from 5 to 44 years (mean, 16 ± 10 years), with 30 children. Intraoperative MEPs improved in 23 (51 %), remained the same in 21 (46.7 %) and worsened in 1 (2 %) patient. Motor improvement occurred in 7 patients and clinical improvement in 17 patients in the immediate postoperative period. Postoperative neurological worsening occurred in one patient (2.2 %). Improved and stable MEPs correlated with the motor (p = 0.002) and clinical improvement (p = 0.02) in the immediate postoperative period. Follow-up was available in 35 patients (77.7 %), ranging from 5 to 24 months (median, 21 months; mean, 17.7 ± 6.8 months). There was late clinical improvement in 73.5 % of the patients in whom the intraoperative MEP had remained the same or improved. However, there was no statistically significant correlation between MEP change and long-term outcome.

CONCLUSIONS

Intraoperative MEP improvement occurs in about 50 % of the patients following successful untethering. This finding probably provides support to the ischemic theory of tethered cord syndrome.

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.

Posterior transthecal approach for repair of cauda equina fibers and ventral dural laceration in lumbar burst fracture: a novel surgical technique

STUDY DESIGN

Retrospective descriptive study of an innovative surgical technique for patients with thoracolumbar fracture.

OBJECTIVE

To describe the transthecal approach for patients with thoracolumbar fracture and demonstrate its safety and effectiveness.

SUMMARY OF BACKGROUND DATA

The goals of surgery in patients with thoracolumbar fracture include neural decompression, re-establishing stability, reduction of deformity, and repair of dural laceration and the damaged neural elements. The traditional posterior approach may only accomplish the former 3 goals.

METHODS

Simply opening the dura during the traditional posterior approach enables accomplishment of all the aforementioned goals, which would not be possible through an anterior or posterior approach alone.

RESULTS

We have successfully performed the transthecal approach in 5 patients with thoracolumbar burst fracture with cauda equina fiber injury. Neural decompression, re-establishing stability, reduction of deformity, and repair of dural laceration and the damaged cauda equina fiber were all achieved in these patients. No complications were noted.

CONCLUSION

The transthecal approach can be applied to patients with thoracolumbar burst fracture to achieve neural decompression, re-establishing stability, reduction of deformity, and repair of dural laceration and the damaged cauda equina fiber. This approach may be an alternative to combined (circumferential) surgery.

LEVEL OF EVIDENCE

4.

[Neurophysiological monitoring during surgery]

BACKGROUND

Intraoperative neurophysiological monitoring has become increasingly important in interventions involving risk of damage to the nervous system. We aim to provide an overview of possibilities and limitations on the use of intraoperative neurophysiological methods.

METHOD

The article is based on a review of relevant textbooks and articles from own literature archives and selective searches in PubMed, combined with the authors' own clinical experience.

RESULTS

Intraoperative neurophysiological monitoring includes both continuous monitoring of neural tissue and localisation of vital neurological structures. This monitoring can reduce the risk of damage to nerves and neural pathways and is used most frequently in scoliosis and neurosurgical operations. The need for neurophysiological monitoring influences the choice of anaesthesia, as some anaesthetics affect the monitoring.

INTERPRETATION

Intraoperative neurophysiological monitoring is dependent on good cooperation between neurophysiologists, surgeons, anaesthetists and the other specialities involved.

Terminal myelocystocele: surgical observations and theory of embryogenesis

BACKGROUND

The structural complexity of terminal myelocystocele (TMC) precludes a recognizable link to spinal cord development and therefore a plausible embryogenetic theory.

OBJECTIVE

To demystify TMC using clinical, imaging, surgical, electrophysiological, and histopathological data and to propose a theory of embryogenesis.

METHODS

Our series consisted of 4 newborns and 6 older children. All had preoperative magnetic resonance imagings and surgical repair of the myelocystocele with electrophysiological monitoring.

RESULTS

TMC can be deconstructed into essential and nonessential features. Essential features are present in all TMCs and constitute the core malformation, comprising an elongated spinal cord extending extraspinally into a cerebrospinal fluid--filled cyst that is broadly adherent to the subcutaneous fat. The functional conus resides in the proximal cyst or within the intraspinal cord, and the caudal myelocystocele wall is nonfunctional fibroneural tissue. Nonessential features include variable measures of hydromyelia, caudal meningocele, and fat, present in only some patients. The core structure of TMC strikingly resembles a transitory stage of late secondary neurulation in chicks in which the cerebrospinal fluid-filled bleblike distal neural tube bulges dorsally to fuse with the surface ectoderm, before focal apoptosis detaches it from the surface and undertakes its final dissolution. We theorize that TMC results from a time-specific paralysis of apoptosis just before the dehiscence of the cystic distal cord from the future skin, thereby preserving the embryonic state.

CONCLUSION

Besides tethering, the myelocystocele may show early rapid expansion causing precipitous deterioration. We recommend early repair with resection of the nonfunctional caudal cyst wall, reconstruction of the proximal neural placode, and duraplasty.

Cauda equina repair in the rat: part 2. Time course of ventral root conduction failure

Treatment for cauda equina (CE) ventral root injury is currently limited. Furthermore, relatively little is known about the time course of nerve root functional degeneration after such injury has occurred. Using a previously developed method for identifying spinal nerve roots that innervate the rat tail, we transected S2, S3, and S4 ventral roots and measured their ability to activate tail muscles out to 72 h post-injury by way of stimulus-evoked electromyography (EMG) recording. Immediately following transection, all distal ventral root stumps successfully activated muscles in the tail upon stimulation with no change in stimulus threshold (0.07±0.04 to 0.07±0.06 V using 0.1-msec pulse duration; 0.04±0.02 to 0.04±0.02 V using 1.0-msec pulse duration). Thresholds increased incrementally at each later time point (24 h: 0.27±0.33 V using 0.1-msec pulse duration; 0.09±0.07 V using 1-msec pulse duration; 48 h: 0.57±1.00 V using 0.1-msec pulse duration; 0.56±1.09 V using 1-msec pulse duration), with the first complete absence of EMG noted at 48 h post-transection in a subset of nerve roots (4/12). We were not able to elicit EMG at 72 h post-transection without moving distally along the nerve root stump. Based on neurofilament staining, only 51% of axons were identifiably intact nearest the site of injury at 24 h post-injury. This percentage dropped to 39% at 48 h, and just 18% at 72 h. Moving 5 mm from the site of injury, we identified 83% intact axons at 24 h post-transection, 77% at 48 h, and 68% at 72 h. Regenerative implications aside, if electrophysiological mapping of injured nerve roots is to be carried out for repair purposes, the rapid nature of conduction failure needs to be considered.