Intraoperative Neurophysiology Research Articles

Practice guidelines for the supervising professional: intraoperative neurophysiological monitoring

The American Society of Neurophysiological Monitoring (ASNM) was founded in 1988 as the American Society of Evoked Potential Monitoring. From the beginning, the Society has been made up of physicians, doctoral degree holders, technologists, and all those interested in furthering the profession. The Society changed its name to the ASNM and held its first Annual Meeting in 1990. It remains the largest worldwide organization dedicated solely to the scientifically based advancement of intraoperative neurophysiology. The primary goal of the ASNM is to assure the quality of patient care during monitored procedures along the neuraxis. This goal is accomplished through programs in education, advocacy of basic and clinical research, and publication of guidelines. The ASNM is committed to the development of medically sound and clinically relevant guidelines for intraoperative neurophysiology. Guidelines are formulated based on exhaustive literature review, recruitment of expert opinion, and broad consensus among ASNM membership. Input is likewise sought from sister societies and related constituencies. Adherence to a literature-based, formalized process characterizes the construction of all ASNM guidelines. The guidelines covering the Professional Practice of intraoperative monitoring were established by a committee of nearly 30 total participants and ultimately endorsed by the Board of Directors of ASNM on January 24th 2013. That document follows.

Intraoperative neurophysiology in tethered cord surgery: techniques and results

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. 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). 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. 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.

Effectiveness of C5 or C6-Cz assembly in predicting immediate post operative facial nerve deficit

Intraoperative neurophysiology monitoring (IOM) is a valuable tool in cerebellopontine angle (CPA) surgeries posing risk to the cranial nerves. Transcranial electrical stimulation (TES) for cranial nerves has been performed in the last 7 years, for obtaining the facial nerve motor evoked potential (MEP), using either C3/C4-Cz or C3-C4 (or inverse) stimulating points, which have been correlated with facial nerve functional outcome. Intraoperative surgical and electrophysiological findings were documented prospectively. Patient files were reviewed for clinical data. We studied 23 patients undergoing CPA tumor resection using C5 or C6-Cz montage for TES, and were able to determine the correlation between facial nerve functional outcome and the amplitude drop of facial MEP above 50 %. Patients were evaluated for immediate facial nerve outcome and 6 months after the surgery. Follow-up was performed by structured telephone interviews with local physicians. The sensibility of the studied parameters was 92.8 % for amplitude drop of facial nerve MEP, with positive predictive value of 81.2 %. The absence of changes during IOM has shown a negative predictive value of 100 %. In this series, the used montage was effective in predicting new facial deficit.

Medicare Changes Some Audiology Codes for 2013

Medicare Changes Some Audiology Codes for 2013

An intraoperative multimodal neurophysiologic approach to successful resection of precentral gyrus epileptogenic lesions

Cortical dysplasias (CDs) are highly epileptogenic lesions with a good prognosis of seizure freedom, if totally resected. However, their accurate delineation and resection can be difficult, and depend on the extent of pathology and lesion location. Intraoperative neurophysiologic assessments are valuable in these situations. We present an illustrative case of intractable epilepsy where judicious use of intraoperative neurophysiologic-techniques guided resection of precentral CD, under general anesthesia and in the absence of preoperative electrophysiologic mapping data. Ictal onset was accurately delineated using electrocorticography (ECoG). Phase reversal of the median somatosensory-evoked potentials (MSSEPs) localized the central sulcus (CS). Motor evoked potentials (MEPs) triggered by high-frequency monopolar anodal electrical cortical stimulation at the primary motor cortex (PMC) threshold delineated the PMC. Using this technique, PMC and the corticospinal tract (CST) were continuously monitored during resection. No changes in MEPs from the preresection baseline were seen; no residual abnormal activity was present in the postresection ECoG. The patient emerged from surgery without deficits and has been seizure free during a 10-month follow-up. Staged multimodal intraoperative neurophysiology can be used successfully under general anesthesia to guide resection of epileptogenic lesions within the precentral gyrus, as an add-on or, in certain situations, as a viable alternative to preoperative electrophysiologic mapping.

Neurophysiologic Intraoperative Monitoring of the Vestibulocochlear Nerve

Neurosurgical procedures involving the skull base and structures within can pose a significant risk of damage to the brain stem and cranial nerves. This can have life-threatening consequences and/or result in devastating neurologic deficits. Over the past decade, intraoperative neurophysiology has significantly evolved and currently offers a great tool for live monitoring of the integrity of nervous structures. Thus, dysfunction can be identified early and prompt modification of the surgical management or operating conditions, leads to avoidance of permanent structural damage.Along these lines, the vestibulocochlear nerve (CN VIII) and, to a greater extent, the auditory pathways as they pass through the brain stem are especially at risk during cerebelopontine angle (CPA), posterior/middle fossa, or brain stem surgery. CN VIII can be damaged by several mechanisms, from vascular compromise to mechanical injury by stretch, compression, dissection, and heat injury. Additionally, cochlea itself can be significantly damaged during temporal bone drilling, by noise, mechanical destruction, or infarction, and because of rupture, occlusion, or vasospasm of the internal auditory artery.CN VIII monitoring can be successfully achieved by live recording of the function of one of its parts, the cochlear or auditory nerve (AN), using the brain stem auditory evoked potentials (BAEPs), electrocochleography (ECochG), and compound nerve action potentials (CNAPs) of the cochlear nerve.This is a review of these techniques, their principle, applications, methodology, interpretation of the evoked responses, and their change from baseline, within the context of surgical and anesthesia environments, and finally the appropriate management of these changes.

P12.6 Intraoperative neurophysiology during surgery for thoraco-abdominal aortic aneurysms type II

P12.6 Intraoperative neurophysiology during surgery for thoraco-abdominal aortic aneurysms type II

Intraoperative neurophysiology in DBS for dystonia

Deep brain stimulation (DBS) of the internal segment of the globus pallidus (GPi) has been demonstrated to be an effective therapy for the treatment of primary dystonia as well as tardive dystonia. Results for other forms of secondary dystonia have been less consistent. Although a number of target sites have been explored for the treatment of dystonia, most notably the motor thalamus, the target of choice remains the sensorimotor portion of the GPi. Although the optimal site within the GPi has not been determined, most centers agree that the optimal site involves the posteroventral lateral "sensorimotor" portion of the GPi. Microelectrode recording (MER) can be used to identify boundaries of the GPi and nearby white matter tracts, including the corticospinal tract and optic tract, and the sensorimotor GPi. However, whether or not the use of MER leads to improved outcomes compared with procedures performed without MER has not been determined. Currently, there is no evidence to support or refute the hypothesis that mapping structures with MER provides better short- or long-term outcomes. Centers using MER do not report a preference of one system over another, but there have not been any studies to compare the relative benefits or risks of using more than 1 electrode simultaneously. Comparison studies of different target structures and targeting techniques in dystonia have not been performed. Additional research, which includes comparative studies, is needed to advance our understanding and optimization of DBS targets, techniques, and approaches along with their relative benefits and risks in dystonia.

Intraoperative Neurophysiology: A Comprehensive Guide to Monitoring and Mapping

Intraoperative Neurophysiology: A Comprehensive Guide to Monitoring and Mapping

Applications of blood oxygenation level dependent-functional magnetic resonance imaging, diffusion tensor imaging and intraoperative neurophysiology monitoring in secondary epileptic surgery in M1 area

To explore the applications of blood oxygenation level dependent-functional magnetic resonance imaging (BOLD-fMRI), diffusion tensor imaging (DTI) and cortical somatosensory evoked potentials (Co-SEP), motor evoked potentials (MEP) and electrocorticogram (ECoG) in secondary epileptic surgery of primary motor area (M1). In 19 patients, preoperative BOLD-fMRI were performed to display the relationship between active zone, fiber bundle and epileptogenic lesions. Besides, Co-SEP, MEP and ECoG were also carried out intra-operatively to direct the resection of epileptogenic lesion and epileptogenic focus. At the same time, the nervous functions were protected as much as possible. Then fMRI was performed again to ensure that the post-operative nervous function was excellent. In preoperative BOLD-fMRI and DTI examinations, active zone and fiber bundle could be seen at the edge of lesions (n = 12); range reduced, become deformed or removed (n = 6); glioma epileptogenic lesion was close-up with M1 (n = 1). The central sulcus was confirmed by Co-SEP in all cases. And two cases were inconsistent with anatomical location; Stimulating precentral gyrus, MEP were elicited post-operatively from orbicularis oris, muscle of thenar, hypothenar muscle or flexor digitorum brevis. Under the monitoring of ECoG, spike-wave was monitored in all cases. Of these, epileptogenic focus was in M1 (n = 15). After treatment, spike-wave were reduced significantly or disappeared. At a post-operative follow-up of 6 - 12 months, seizure improvement has achieved Engel III level or above (n = 18). On re-examinations of BOLD-fMRI and DTI, active zone became bigger than before and fiber bundle was symmetric with opposite side. Two of 19 cases had transient motor aphasia incompletely or hemiparesis. No permanent neurological dysfunction occurred. There was no relapse in cases of glioma. BOLD-fMRI and Co-SEP, MEP and ECoG are complementary in M1 of secondary epilepsy surgery. It is effective to preserve nervous functions and enhance the quality of life for patients with epilepsy.

Surgical treatment of high-grade gliomas in motor areas. The impact of different supportive technologies: a 171-patient series

In the last few years much has been published to validate new technology in brain mapping for clinical purposes, but there have been few clinical results. In this report we describe our five-year experience in the surgical management of malignant gliomas around motor areas with an evaluation of the impact of functional magnetic resonance imaging (fMRI) plus navigator and intraoperative neurophysiology (IN). End-points were extent of removal, morbidity, and survival. Variables describing patient and tumor characteristics and treatment modalities were statistically weighted in relation to treatment outcome. Tumor depth (P = 0.01), midline shift ≥1 cm. (P = 0.05), and insular location (P = 0.001) negatively affected extent of removal, whereas IN (P < 0.001) and fMRI plus navigator (P = 0.02) contributed to increasing the rate of total removal (73%, 71% vs. 40%). Postoperative motor impairment was mild and transient in a minority of cases (20%). General complications, as defined by the Glioma Outcome Project, occurred in 23% of cases. IN was the only factor associated with acute postoperative motor deterioration (P < 0.001). IN and age >65 years (P = 0.01) were associated with the occurrence of complications. Overall survival was significantly higher in patients operated with IN or fMRI plus navigator (P < 0.01). Comparing different surgical strategies used in the same period, we observed that supportive technologies in glioma surgery have their primary impact on the quality of resection and survival. IN led to transient motor impairment and some additional complications which did not affect functional outcome.

Do we still need invasive recordings? If so for how much longer?

This paper was presented at the International Society for Pediatric Neurosurgery Meeting in Cape Town in October 2008 during the post-meeting Focus Session on Intraoperative Neurophysiology. It reflects the personal views of the author and is intended as a pragmatic approach to cases where a non-invasive pre-surgical evaluation has not been successful in localising the epileptogenic zone. It is based on the experience of the multi-disciplinary team at Great Ormond Street Hospital without whose support none of the surgical work would be possible.

Intraoperative neurophysiology of the motor system in children

Intraoperative neurophysiology of the motor system in children

Intraoperative neurophysiology is here to stay

The 2010 February and April issues of Child’s Nervous System offer to the readers two very timely focus sessions in the field of “neuromonitoring”. This was the topic of a symposium held in Cape Town in October 2008—as a satellite event of the 36th Meeting of the International Society for Pediatric Neurosurgery—aimed to cover the various techniques available to neurosurgeons for keeping under control the brain and the spinal cord, both in the operating room and the intensive care unit. What emerged from that symposium is presented in these focus sessions, where international experts in traumatic brain injury (see the Editorial of Dr. Figaji in the February issue of Child’s Nervous System) and intraoperative neurophysiology address the aspects of these disciplines relevant to pediatric neurosurgery.

Intraoperative neurophysiology of the motor system in children: a tailored approach

Intraoperative neurophysiology has moved giant steps forward over the past 15 years thanks to the advent of techniques aimed to reliably assess the functional integrity of motor areas and pathways. Motor evoked potentials recorded from the muscles and/or the spinal cord (D-wave) after transcranial electrical stimulation allow to preserve the integrity of descending pathways, especially the corticospinal tract (CT), during brain and spinal cord surgery. Mapping techniques allow to identify the motor cortex through direct cortical stimulation and to localize the CT at subcortical levels during brain and brainstem surgery. These techniques are extensively used in adult neurosurgery and, in their principles, can be applied to children. However, especially in younger children, the motor system is still under development, making both mapping and monitoring techniques more challenging. In this paper, we review intraoperative neurophysiological techniques commonly used in adult neurosurgery and discuss their application to pediatric neurosurgery, in the light of preliminary experience from our and other centers. The principles of development and maturation of the motor system, and especially of the CT, are reviewed focusing on clinical studies with transcranial magnetical stimulation.

Intraoperative neurophysiology for surgery in and around the brainstem: role of brainstem mapping and corticobulbar tract motor-evoked potential monitoring

New advancements of intraoperative neurophysiology for surgery in and around the brainstem have been described. NEUROPHYSIOLOGICAL TECHNIQUES: Brainstem mapping (BSM) is applied to locate cranial nerves and their motor nuclei (CMN) on the floor of the fourth ventricle. Corticobulbar tract (CBT) motor-evoked potential (MEP) monitoring is used to achieve on-line monitoring of the cranial motor nerves' functional integrity. Each of these procedures bears a specific role: BSM can help avoid direct damage to CMNs on the fourth ventricular floor; CBT-MEP can provide simultaneous feedback on the functional integrity of the CBT and CMN during surgery, eventually leading to "tailored" modifications of the surgical procedure, based upon neurophysiological responses. CBT-MEP monitoring has less restriction in terms of clinical indications, but a combination of both procedures is essential for functional preservation of CMNs during surgery in and around the brainstem.

Combined radiofrequency and kyphoplasty in painful osteolytic metastases to vertebral bodies

The aim of this study was to assess retrospectively the safety and efficacy of combined radiofrequency (RF) and kyphoplasty (KP) in managing painful osteolytic metastases to vertebral bodies resistant to conservative treatments. Eleven patients (9 women and 2 men; mean age 68 years; age range 58-82) with painful osteolytic vertebral body metastases unresponsive to conservative treatments underwent RF combined with KP under general anaesthesia. Primary neoplasms were kidney carcinoma (n=1), breast carcinoma (n=1), thyroid carcinoma (n=2) and multiple myeloma (n=7). Lesion levels were cervical (n=1), thoracic (n=9) and lumbar (n=1). Combined RF and KP was well-tolerated by all patients. The procedures were performed using fluoroscopic guidance and intraoperative neurophysiology monitoring. Pain relief with the visual analogue scale (VAS) pain score and analgesic consumption were evaluated before and after treatment. No complication occurred. In one case, we observed an asymptomatic cement leakage. Pain significantly decreased after treatment: the mean VAS pain score before treatment was 8 (range 7-10) vs. 1.8 (range 0-3) and 1.9 (range 1-3), respectively, 72 h and 6 weeks after the treatment. Analgesic reduction was achieved in all patients. RF combined with KP represents a potential alternative method for palliation of painful spinal osteolytic metastases in selected patients. The procedures are safe and provide pain relief with bone augmentation and improvement in quality of life.

Comment on “Typical variations of subthalamic electrode location do not predict limb motor function improvement in Parkinson’s disease”

McClelland et al. have produced a methodical, albeit small and retrospective, study that suggests a degree of clinical tolerance compensating for variations in lead location within the subthalamic nucleus (STN). They did not analyse electrode position in relation to the STN itself, but rather in relation to its intended position. Their series of operations was performed at least 8 years to 9 years ago, and significant improvements in the quality of imaging of the STN have occurred since. The technique of indirect targeting, as was used in the study by McClelland et al., is now less commonly used. A recognition of individual variation in anatomy, together with vastly improved anatomical delineation of the STN with modern MRI, have resulted in most centres adopting direct targeting (with or without intraoperative neurophysiology). 1 Rather than the position of the STN being inferred, it is seen relatively clearly on preoperative MRI scanning. A further limitation of this study is the lack of discussion of whether intraoperative macrostimulation was used to determine clinical efficacy and to guide final electrode placement. It appears to have been used only to determine side effects. In addition, two different electrode types were used in this study, introducing a potential confounder. If the goal of surgery is to ameliorate Parkinsonian symptoms, it would make sense that intraoperative stimulation should be used to determine not only the likely side effects, but also the potential benefits. In other words, intraoperative stimulation may provide valuable information with respect to a ‘‘therapeutic window”. This study does support the notion that indirect targeting, combined with microelectrode recording and limited macrostimulation, can produce consistent results in terms of motor benefits. Importantly, it did not examine whether variations in electrode placement had a significant impact on neuropsychological outcomes, an area of increasing concern in this burgeoning field.

Diagnosis and treatment of pudendal nerve entrapment syndrome subtypes: imaging, injections, and minimal access surgery

To improve diagnostic accuracy and achieve high levels of treatment success in patients with pudendal nerve entrapment (PNE) syndromes, the author of this study applied advanced technology diagnostics in distinguishing the various syndrome types according to the different entrapment locations and evaluated new minimal access surgical techniques to treat each subtype. Two hundred cases were prospectively evaluated using a standardized set of patient-completed functional and symptom assessments, a collection of new physical examination maneuvers, MR neurography, open MR image-guided injections, intraoperative neurophysiology, minimal access surgery, and formal outcome assessment with the Oswestry Disability Index, pain diagrams, and analog pain scales. Four primary types of PNE syndromes were identified based on the different locations of entrapment: Type I, entrapment at the exit of the greater sciatic notch in concert with piriformis muscle spasm; Type II, entrapment at the level of the ischial spine, sacrotuberous ligament, and lesser sciatic notch entrance; Type III, entrapment in association with obturator internus muscle spasm at the entrance of the Alcock canal; and Type IV, distal entrapment of terminal branches. The application of new, targeted minimal access surgical techniques led to sustained good to excellent outcomes (50-100% improvement in the pain score or functional score) in 87% of patients. Most of these patients obtained most of their improvement within 4 weeks of surgery, although some continued to experience progressive improvements up to 12 months after surgery. The application of advanced diagnostics to categorize PNE syndrome origins into 4 major subtypes and the subsequent treatment of each subtype with a tailored strategy greatly improved therapeutic outcomes as compared with those reported when only a single treatment paradigm was applied to all patients.

Current opinions and recommendations on multimodal intraoperative monitoring during spine surgeries

With the rapid development of imaging techniques and better understanding of structural and functional pathology of the spine and spinal cord there has been a worldwide increase in the number of spine surgeries performed, particularly in specialized interdisciplinary spine centers. In addition to the congenital and acquired deformities of the spine and relatively rare spinal cord tumors, common degenerative spine disease within the aging general population contributes to a growing number of pathologies with myelopathies. This is important because antecedent myelopathy increases spinal cord risk during surgical treatment. The possibility of having functional neurophysiological assessment during spine and spinal cord surgery was introduced in 1970s by applying somatosensory evoked potentials (SEPs) as well as spinal evoked potentials [15, 21, 32, 33]. Meanwhile these modalities and continuous EMG recording have been enhanced by the addition of corticospinal motor pathway monitoring through the use of motor evoked potentials (MEPs) elicited by transcranial electrical stimulation [3]. The application of multimodal intraoperative monitoring (MIOM) became routine in several spine centers, being documented by publications about the specificity and sensitivity as well as clinical experience and outcome measurements during different spinal surgical procedures [6, 9, 13, 14, 17, 22, 24, 26, 27]. In this supplement on intraoperative monitoring the Spine Center of the Schulthess Clinic presents their experience with the application of MIOM during spine surgery analyzing 1,017 operations in the years 2000–2005. The patients for monitoring were selected out of 11,356 who received spine surgery at the institution during the study period. The indication for each monitoring procedure was discussed and established within the monitoring and surgical team. The detailed analysis of this large patient population resulted in a sensitivity of 89% and specificity of 99%. Sutter et al. [31] conclude that MIOM is an effective method of monitoring the spinal cord functional integrity during spine surgery and therefore can lead to reduction of neurological deficits and consequently improve postoperative results. An independent series of 206 thoracolumbar surgeries also presented in this supplement supports this conclusion [19]. Sala et al. [27] discussed in their recent publication of a historical control study the ethical limitation for performing prospective randomized studies to assess the efficacy of MIOM while clearly documenting that monitoring improves outcome after surgery for intramedullary spinal tumors. The Spine Society of Europe (SSE) supported the development of MIOM by presentations of the results at its annual meetings and organized workshops to stimulate discussion and communication between the spine surgeons and clinical neuroscientists. The SSE has also introduced quality control management in spine surgeries by establishing Spine Tango, a web-based international registry that includes MIOM documentation (http://www.eurospine.org). Other international spine societies such as Scoliosis Research Society presented several original papers on MIOM at the 41st annual meeting in 2006 [2, 5, 23] illustrating its advantages for surgery of adolescent idiopathic and infantile scoliosis. Recently, the International Society of Intraoperative Neurophysiology (ISIN) was founded to stimulate interdisciplinary communication and collaboration between surgeons, neurologists, neurophysiologists and anesthetists (http://www.ptsroma.it/isin). The aim of a first consensus meeting on intraoperative monitoring during spine surgeries in Verona (28 September 2006) was to provide recommendations for the improvement and appropriate application of monitoring techniques during spine surgeries. Experts in the field were invited for a meeting with the support of the European Spine Journal (Max Aebi, MD, Editor-in-chief, Marek Szpalski, MD, Supplement Editor) to summarize the current state-of-the-art and prepare current opinions and recommendations. This consensus statement represents a work in progress and as with all other recommendations or proposals, it must be updated as new information is gained.