Intraoperative neuromonitoring as real-time diagnostic for cerebral ischemia in endovascular treatment of ruptured brain aneurysms.

OBJECTIVE: To evaluate the diagnostic accuracy of intraoperative neurophysiological monitoring (IONM) during endovascular treatment (EVT) of ruptured intracranial aneurysms (rIA). METHODS: IONM and clinical data from 323 patients who underwent EVT for rIA from 2014-2019 were retrospectively reviewed. Significant IONM changes and outcomes were evaluated based on visual review of data and clinical documentation. RESULTS: Of the 323 patients undergoing EVT, significant IONM changes were noted in 30 patients (9.29%) and 46 (14.24%) experienced postprocedural neurological deficits (PPND). 22 out of 30 (73.33%) patients who had significant IONM changes experienced PPND. Univariable analysis showed changes in somatosensory evoked potential (SSEP) and electroencephalogram (EEG) were associated with PPND (p-values: <0.001 and <0.001, retrospectively). Multivariable analysis showed that IONM changes were significantly associated with PPND (Odd ratio (OR) 20.18 (95%CI:7.40-55.03, p-value: <0.001)). Simultaneous changes in both IONM modalities had specificity of 98.9% (95% CI: 97.1%-99.7%). While sensitivity when either modality had a change was 47.8% (95% CI: 33.9%-62.0%) to predict PPND. CONCLUSIONS: Significant IONM changes during EVT for rIA are associated with an increased risk of PPND. SIGNIFICANCE: IONM can be used confidently as a real time neurophysiological diagnostic guide for impending neurological deficits during EVT treatment of rIA.

Different cutoff value of motor evoked potentials for the postoperative outcome in the ossification of the posterior longitudinal ligament surgery in the cervical and thoracic spine.

BACKGROUND CONTEXT: Transcranial muscle motor evoked potentials (Tc-mMEPs), a key component of intraoperative neurophysiologic monitoring (IONM), effectively reflect the changes in corticospinal tract integrity and are closely related to the occurrence of the postoperative motor deficit (PMD). Most institutions have applied a specified (fixed) alarm criterion for the heterogeneous groups in terms of etiologies or lesion location. However, given the high risk of PMD in ossification of the posterior longitudinal ligament (OPLL) surgery, it is essential to determine a tailored cutoff value for IONM. PURPOSE: We aimed to establish the intraoperative cutoff value of Tc-mMEPs reduction for predicting PMD in OPLL according to lesion levels. DESIGN: Retrospective analysis using a review of electrical medical records. PATIENT SAMPLE: In this study, we included 126 patients diagnosed with OPLL, who underwent surgery and IONM. OUTCOME MEASURES: The occurrence of PMD immediately and 1 year after operation, as well as the decrement of intraoperative Tc-mMEPs amplitude. METHODS: We analyzed OPLL surgery outcomes using Tc-mMEPs monitoring. Limbs with acceptable baseline Tc-mMEPs in the tibialis anterior or abductor hallucis were included in the final set. PMD was defined as a ≥1 decrease in Medical Research Council score in the legs, and it was evaluated immediately and 1year after operation. The reduction ratios of Tc-mMEPs amplitude compared with baseline value were calculated at the two time points: the maximal decrement during surgery and at the end of surgery. Receiver operating characteristic curve analysis was used to determine the cutoff value of Tc-mMEPs amplitude decrement for predicting PMDs. RESULTS: In total, 203 limbs from 102 patients with cervical OPLL and 42 limbs from 24 patients with thoracic OPLL were included. PMD developed more frequently in thoracic lesions than in cervical lesions (immediate, 9.52% vs 2.46%; 1 year, 4.76% vs 0.99%). The Tc-mMEPs amplitude cutoff point at the end of surgery for PMD (both immediate and 1-year) was a decrease of 93% in cervical and 50% in thoracic OPLL surgeries. Similarly, the Tc-mMEPs amplitude cutoff point at the maximal decrement during surgery for PMD (both immediate and 1 year) was a reduction of 97% in cervical and 85% in thoracic OPLL surgeries. CONCLUSIONS: The thoracic lesion exhibited a lower cutoff value than the cervical lesion for both immediate and long-term persistent PMD in OPLL surgery (Tc-mMEPs at the end of surgery measuring 93% vs 50%; and Tc-mMEPs at the maximal decrement measuring 97% vs 85% for cervical and thoracic lesions, respectively). To enhance the reliability of monitoring, considering the application of tailored alarm criteria for Tc-mMEPs changes based on lesion location in OPLL could be beneficial.

New frontiers in intraoperative neurophysiologic monitoring: a narrative review.

Background and Objective: Neurological insults during surgery arise from anatomic and/or physiologic perturbations. Intraoperative neurophysiologic monitoring (IONM) fills a critical role of ensuring that any neurological insults during certain surgical procedures are caught in real-time to prevent patient harm. IONM provides immediate feedback to the surgeon and anesthesiologist about the need for an intervention to prevent a neurologic deficit postoperatively. As important as it seems to have IONM available to any patient having surgery where a neurological injury is possible, the truth is that IONM is unavailable to large swaths of people around the world. This review is intended to bring attention to all of the ways IONM is critically important for a variety of surgeries and highlight the barriers preventing most patients around the world from benefiting from the technology. Expansion of IONM to benefit patients from all over the world is the new frontier. Methods: We searched all English language original papers and reviews using Embase and MEDLINE/PubMed databases published from 1995 to 2022. Different combinations of the following search terms were used: intraoperative neuromonitoring, neurosurgery, low-income countries, cost, safety, and efficacy. Key Content and Findings: We describe common IONM modalities used during surgery as well as explore barriers to implementation of IONM in resource-limited regions. Additionally, we describe ongoing efforts to establish IONM capabilities in new locations around the world. Conclusions: In this paper, we performed a review of the literature on IONM with an emphasis on the basic understanding of clinical applications and the barriers for expansion into resource-limited settings. Finally, we provide our interpretation of "new frontiers" in IONM quite literally facilitating access to the tools and education so a hospital in Sub-Saharan Africa can incorporate IONM for their high-risk surgeries.

Intraoperative Neurophysiologic Monitoring in Predicting Dysphagia After Brainstem and Fourth Ventricle Surgery.

OBJECTIVE: Dysphagia represents the main complication of posterior fossa neurosurgery. Adequate diagnosis of this complication is warranted to prevent untimely extubation with subsequent aspiration. Intraoperative neurophysiologic monitoring (IONM) modalities may be used for this purpose. However, it is not known which IONM modality may be significant for diagnosis. This study aimed to define the most significant IONM modality for dysphagia prognostication after posterior fossa neurosurgery. METHODS: The analysis included 46 patients (34 with tumors of the fourth ventricle and 12 with brainstem localization) who underwent surgical excision of the tumor. Neurologic symptoms before and after neurosurgery were noted and magnetic resonance imaging with the subsequent volume estimation of the removed mass was performed, followed by an IONM findings analysis (mapping of the nucleus of the caudal cranial nerves [CN] and corticobulbar motor-evoked potentials [CoMEP]). RESULTS: Aggravation of dysphagia was noted in 24% of the patients, more often in patients with tumor localization in the fourth ventricle (26%) than in those with brainstem mass lesions (16%). Mapping of the caudal cranial nerve nuclei did not correlate with the dysfunction of these structures. CoMEP was significantly associated with the neurologic state of the CN. The decrease in CoMEP is a significant prognostic factor for postoperative bulbar symptoms appearance or aggravation. CONCLUSIONS: Mapping the CN is an important identification tool. The CoMEP modality should be used intraoperatively to determine the functional state of the CN and predict postoperative dysphagia.

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

OBJECTIVE: Spinal schwannomas (SS) and spinal meningiomas (SM) account for most intradural extramedullary (IDEM) tumors. These tumors are usually benign lesions, which generally respond favorably to surgical excision. Few studies up to now tried to determine the long-term outcome after minimally invasive surgery (MIS) with multimodal intraoperative neurophysiological monitoring (IONM) for IDEM tumors. The aim of this study was to present one of the largest case series with special regard to IONM findings and long-term outcome after MIS-keyhole surgery with a tubular retractor system. METHODS: Between January 2013 and August 2018, 87 patients with IDEM tumors who underwent tumor removal surgery via MIS-keyhole approach under multimodal IONM were retrospectively reviewed. The neurological status was assessed using a modified McCormick grading scale pre- and postoperatively. Multimodal IONM consisted of motor evoked potentials (MEP), somatosensory evoked potentials (SEP), and electromyography (EMG). Both short-term and long-term clinical evaluations as well as patients' medical files were retrospectively analyzed. RESULTS: Surgeries were performed for resection of SS in 49 patients and SM in 38 patients. Tumor locations were cervical in 16.1%, thoracic in 48.3%, thoracolumbar in 4.6%, lumbar 31%. Critical IONM changes were detected in 9 operations (10.3%) in which there were 2 SEPs, 5 MEPs, and 2 EMG events. Three IONM changes (2 MEPs, 1 EMG) were turned out to be transient change in nature since they were resolved in a short time when immediate corrective actions were initiated. Six patients with permanent IONM changes (2SEPs, 3MEPs, 1EMG event), all deficits had resolved during hospitalization or on short -term follow-up evaluation. Sensitivity, specificity, and positive and negative predicted values of IONM were 100, 96, 67, and 100%, respectively. Gross total resection rate was 100%, and a stable or improved McCormick grade exhibited in all patients. No tumor recurrence and no spinal instability were found in the long-term follow-up evaluation (mean 5.2 ± 2.9 years postoperatively). Overall, 94% of patients were either satisfied or very satisfied with their operation, and 93% patients reported excellent or good general clinical outcome according to Odom's criteria. CONCLUSION: MIS-keyhole surgery with multimodal IONM for IDEM tumors enables a high level of satisfaction and a satisfying long-term clinical and surgical outcome.

Diagnostic Accuracy of Somatosensory Evoked Potentials and Electroencephalography During Endovascular Treatment of Unruptured Cerebral Aneurysms.

OBJECTIVE: Endovascular treatment (EVT) of unruptured cerebral aneurysms (UCA) offers a safer alternative to clipping. However, it is still associated with an increased risk for Postprocedural Neurological deficit (PPND). Prompt recognition using intraoperative neurophysiologic monitoring (IONM) and intervention can reduce the incidence and impact of new postoperative neurological complications. We aim to evaluate the diagnostic accuracy of IONM in predicting PPND after EVT of UCA. METHODS: We included 414 patients who underwent EVT for UCA from 2014 to 2019. The sensitivities, specificities, and diagnostic odds ratio of somatosensory evoked potentials and electroencephalography monitoring methods were calculated. We also determined their diagnostic accuracy using receiver operating characteristic plots. RESULTS: The highest sensitivity of 67.7% (95% confidence interval {CI}, 34.9%-90.1%) was obtained when either modality had a change. Simultaneous changes in both modalities have the highest specificity of 97.8% (95% CI, 95.8%-99.0%). The area under the receiver operating characteristic curve was 0.795 (95% CI, 0.655-0.935) for changes in either modality. CONCLUSIONS: IONM with somatosensory evoked potentials alone or in combination with electroencephalography has high diagnostic accuracy in detecting periprocedural complications and resultant PPND during EVT of UCA.

Clipping of Unruptured Anterior Choroidal Artery Aneurysms Together with Small Branches: Safety Confirmation Using Intraoperative Indocyanine Green Video-Angiography and Intraoperative Neurophysiological Monitoring.

BACKGROUND: In treating anterior choroidal artery (AChA) aneurysms, preserving the AChA main trunk is of course necessary to prevent postoperative ischemic complications. However, in practice, complete occlusions are often limited by small branches. OBJECTIVE: We aimed to demonstrate that even in cases where complete occlusion of the AChA aneurysm is complex due to small branches, complete occlusion can be safely achieved using indocyanine green video-angiography and intraoperative neurophysiological monitoring (IONM). METHODS: We performed a retrospective review of all unruptured AChA aneurysms surgically treated at our institution from 2012 to 2021. All available surgical videos were reviewed to find AChA aneurysms clipped with small branches; clinical and radiological data were collected for these cases. RESULTS: Among 391 cases of unruptured AChA aneurysms treated surgically, 25 AChA aneurysms were clipped with small branches. AChA-related ischemic complications occurred in 2 cases (8%) without retrograde indocyanine green filling to the branches. These 2 cases had changes in IONM. There were no ischemic complications in the remaining cases with retrograde indocyanine green filling to the branches and no change in IONM. During an average follow-up of 47 months (12-111 months), a small residual neck was observed in 3 cases (12%) and recurrence or progression of the aneurysm was observed in only 1 case (4%). CONCLUSIONS: The surgical treatment of AChA aneurysms carries the risk of devastating ischemic complications. Even in cases where complete clip ligation seems impossible due to small branches associated with AChA aneurysms, complete occlusion can be safely achieved using indocyanine green video-angiography and IONM.

Risk Factors and Exit Strategy of Intraoperative Neurophysiological Monitoring Alert During Deformity Correction for Adolescent Idiopathic Scoliosis.

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: To elucidate the risk factors of intraoperative neurophysiological monitoring (IONM) alert during deformity correction surgery for adolescent idiopathic scoliosis (AIS) and to describe the outcomes of patients who underwent staged correction surgery due to IONM alert during the initial procedure. METHODS: We reviewed 1 024 patients with idiopathic scoliosis who underwent deformity correction and were followed-up for ≥1 year. The pre-and postoperative Cobb angle of the major structural curve, operative time, estimated blood loss (EBL), number of levels fused, event that caused the IONM alert, and intervention required for the recovery of the signal were recorded. Patients who received IONM alerts (alert group) and those who did not (non-alert group) during the operation were compared. RESULTS: Compared to the non-alert group, the alert group had a significantly greater preoperative Cobb angle of the major structural curve (P < .001), number of levels fused (P = .003), operative time (P < .001), and EBL (P < .001). The percentage of correction did not significantly differ between the 2 groups (P = .348). Eight patients (.8%) underwent a staged operation because the IONM signal alert hindered correction of the deformity. The percentage of correction of patients who underwent staged operation was 64.9 ± 15.1%, and no permanent neurologic deficits occurred. CONCLUSIONS: A greater magnitude of preoperative deformity and surgical extent increases the risk of cord injury identified by IONM alerts during correction of deformities in patients with AIS. However, in patients in whom the IONM alert cannot be recovered or reproduced by proceeding with deformity correction, surgeons can minimize the risk by aborting the initial procedure and completing the correction using staged operations.

Intraoperative Motor Evoked Responses to Double-Train Paradigm Stimulation for Guiding Lead Placement and Postoperative Programming in Spinal Cord Stimulation for Pain.

OBJECTIVE: We aimed to demonstrate the feasibility of using motor evoked responses to intraoperative double-train stimulation to guide lead placement and matching of intraoperative contacts with postoperative electrode programming in spinal cord stimulation for pain performed under general anesthesia. MATERIALS AND METHODS: The study included a series of 20 consecutive patients with refractory pain operated on under general anesthesia. Either percutaneous or paddle leads were implanted and positioned according to the intraoperative mapping results. Neurophysiologic mapping was performed with a double-train stimulation paradigm (intertrain interval of 60 milliseconds, three to five cathodal pulses with 0.5-millisecond pulse duration, and within-train interstimulus intervals of 2-4 milliseconds). The sites where dorsal column responses of the targeted dermatomes were detected were considered optimal for lead placement (intraoperative best contacts). Following spinal cord stimulator (SCS) lead placement, blinded postoperative programming of electrode contacts was matched with the intraoperative best contacts and the pain-paresthesia overlap for the trial phase. A binominal test was used as a statistical method; pre- and postoperative numeric rating scale (NRS) after three months was obtained. RESULTS: A total of 15 patients underwent spinal cord stimulation trial for intractable pain. Of these, ten patients (66%) had a successful trial and received permanent implants; one patient had a successful trial but was never intended to be implanted because of her poor health condition; four patients (26%) had an unsuccessful trial, leading to trial electrode explantation; and five patients had already had an implant with percutaneous leads and therefore underwent electrode revision, of whom four patients received paddle leads. In 18 of the 20 operated patients (90%), we found a match between the best intraoperative contacts and the postoperatively programmed contacts (significantly better than chance, p = 8.2 × 10-15). In 90% of the patients, a pain-paresthesia overlap of 100% was found. In the remaining two patients (10%), the postoperatively best programmed contacts were one contact away from the intraoperative neurophysiologic best contact. A mean preoperative NRS score of 8.2 (variance) and a mean follow-up NRS score after three months of 3.6 (variance) were obtained for all patients with implants. CONCLUSION: In this proof-of-concept study, we were able to demonstrate that SCS lead placement using a double-train stimulation paradigm performed under general anesthesia is a safe and feasible technique, offering reliable prediction of contacts for postoperative programming and excellent pain-paresthesia coverage.

The feasibility of laryngeal nerve protection during thyroidectomy using sternocleidomastoid intermuscular approach with intraoperative neuromonitoring: a case series and step-by-step description of surgical procedure.

Background: Thyroid surgery is increasingly demanding in terms of cosmetic neck outcomes and protection of anterior neck function, so we have adopted an alternative sternocleidomastoid intermuscular approach (SMIA) for open/conventional thyroidectomy. The protection of recurrent laryngeal nerve (RLN) and external branch of superior laryngeal nerve (EBSLN) is the key and difficult point in thyroid surgery. The aim of this study was to testify the feasibility of RLN and EBSLN functional protection during SMIA thyroidectomy with the intraoperative neuromonitoring. Methods: A total of 39 patients and 39 RLN and EBSLNs who underwent monitored SMIA thyroidectomy were included. Thyroid gland is revealed and excised anterior to the cervical sheath between the sternal and clavicular heads of the sternocleidomastoid muscle. Standardized intraoperative neuromonitoring (IONM) procedures and postoperative laryngeal examination were performed to audit the SMIA. Following the four-step method, V1, R1, R2, and V2 were monitored and the signal values were recorded. Statistical analysis was used to evaluate the change of IONM amplitude of RLN, combined with the results of laryngoscopy before and after operation to determine the status of RLN. EBSLN injuries were identified from changes in cricothyroid muscle (CTM) twitch and EMG. SMIA video vignette is detailed. Results: All RLN and EBSLNs [17 on the left and 22 on the right] were monitored in 39 patients [5 men, 34 women; mean age 34.1±8.7 years; mean body mass index 22.5 (±3.0, 17.0-30.8) kg/m2] undergoing SMIA. For RLN of the affected side, we compared the V2 and V1 (1,236±672 vs. 1,240±428, P=0.973), R2 and R1 (1,676±778 vs. 1,656±765, P=0.849) signals separately, and the results were not statistically different (P>0.05). Comparing the V1 (1,240±428 vs. 1,309±395, P=0.601) signals of the bilateral recurrent laryngeal nerve, there was no statistical difference (P>0.05). CTM twitch and EMG were preserved. Conclusions: The SMIA technique appears feasible. RLN and EBSLN are easier to be exposed during thyroid surgery of SMIA, which is beneficial to the neuroprotection during the operation. At the same time, it can protect the anterior cervical function and improve the cosmetic effect after operation.

Endovascular assisted vertebrobasilar junction aneurysm clipping in a hybrid operation room. Case report.

Introduction: We present a case of a 60-year-old female that underwent surgery for clipping a right vertebrobasilar junction aneurysm (VBJA) in a hybrid operation room. Research question: Does the retrograde suction technique with a proximal balloon is safe and effective as an adjuvant technique in surgery of VBJA? Material and methods: After an extended retrosigmoid approach was performed, a 6F Neuron catheter with an intermediate multipurpose catheter were navigated to the right vertebral artery (VA) through a 6-French sheath, which caused a severe catheter-induced vasospasm in the right VA. The aneurysm was then deflated and clipped. After the withdrawal of the catheter the vasospasm was resolved. Results: The patient had a good recovery, with VI cranial nerve palsy and mild dysphagia due to mild right vocal cord palsy, both improving at 1-month follow-up and fully recovered at 6-month follow-up. Discussion and conclusion: The combination of endovascular procedures and microsurgery at the same hybrid operation room in that case resulted in a safe and effective technique. It is an interesting tool that could help neurosurgeons deal with certain selected cases of VBJA. Intraoperative angiography offers the possibility to reposition a misplaced clip in the same surgery. Good collaboration between interventional neuroradiologists and vascular neurosurgeons helps in achieving good results in such difficult cases.

Intraoperative neurophysiologic monitoring alteration during en bloc laminectomy surgery for thoracic ossification of ligamentum flavum.

Background: There is real risk during en bloc resection for the treatment of thoracic ossification of ligamentum flavum (TOLF). Intraoperative neurophysiologic monitoring (IONM) has been applied to monitor neurologic functional integration of the spinal cord during surgery. However, the IONM outcome and its relationship with clinical results still needs to be investigated. The purpose of this study is to evaluate the effectiveness and usefulness of IONM in en bloc laminectomy for TOLF. Methods: Data from a total of 68 patients with TOLF who received en bloc resection was collected for this retrospective study. IONM of somatosensory-evoked potentials (SSEPs) and motor-evoked potentials (MEPs) were analyzed in different patterns of signal alerts, i.e. alert in either MEPs or SSEPs, alert in both MEPs and SSEPs, permanent alert, or recovery during surgery. Postoperative motor and sensory neurological function was evaluated in each patient immediately after surgery and at 12-month follow-up after surgery. The relationship of IONM outcomes and postoperative neurologic function were observed. Results: Fifty of 68 patients did not present significant changes over alert criteria of IONM, neither SSEPs nor MEPs. Those 50 patients without IONM alerts did not show post-operative neurologic deterioration. Four patients presented alert of IONM in a single modality, while 2 patients showed only SSEP alert and 2 patients showed only MEP alert. Fourteen patients showed alerts in both SSEP and MEP, while 8 patients showed one or both signals return to normal during surgery and other 6 showed permanent abnormal electrophysiologic signals to the end of surgery. In the follow-up neurologic test, 3 patients presented transient neurologic complications from among 8 patients with both SSEP and MEP alerts and recovery during surgery. Six patients without recovery of IONM showed permanent neurologic complications after surgery. Conclusions: Results of this study prove the effectiveness and usefulness of IONM in in en bloc laminectomy surgery for TOLF. The patterns of IONM changes correlated with postoperative neurologic functions. Special attention must be paid to the rapid loss of IONM without recovery during spinal decompression.

Coordination of Intraoperative Neurophysiologic Monitoring Technologist and Surgery Schedules.

Resource coordination in surgical scheduling remains challenging in health care delivery systems. This is especially the case in highly-specialized settings such as coordinating Intraoperative Neurophysiologic Monitoring (IONM) resources. Inefficient coordination yields higher costs, limited access to care, and creates constraints to surgical quality and outcomes. To maximize utilization of IONM resources, optimization-based algorithms are proposed to effectively schedule IONM surgical cases and technologists and evaluate staffing needs. Data with 10 days of case volumes, their surgery durations, and technologist staffing was used to demonstrate method effectiveness. An iterative optimization-based model that determines both optimal surgery and technologist start time (operational scenario 4) was built in an Excel spreadsheet along with Excel's Solver settings. It was compared with current practice (operational scenario 1) and optimization solution on only surgery start time (operational scenario 2) or technologist start time (operational scenario 3). Comparisons are made with respect to technologist overtime and under-utilization time. The results conclude that scenario 4 significantly reduces overtime by 74% and under-utilization time by 86% as well as technologist needs by 10%. For practices that do not have flexibility to alter surgeon preference on surgery start time or IONM technologist staffing levels, both scenarios 2 and 3 also result in substantial reductions in technologist overtime and under-utilization. Moreover, IONM technologist staffing options are discussed to accommodate technologist preferences and set constraints for surgical case scheduling. All optimization-based approaches presented in this paper are able to improve utilization of IONM resources and ultimately improve the coordination and efficiency of highly-specialized resources.

Neurophysiologic monitoring during cervical traction in a pediatric patient with severe cognitive disability and atlantoaxial instability.

Background: Surgical management of atlantoaxial instability (AAI) in pediatric patients with Down syndrome is associated with high neurological morbidity. Moreover, Down syndrome cognitive impairment coupled to AAI removes traditional verbal communication to relay evolving symptoms and aid in neurologic examination. It is not clear whether surgical adjuncts can alter clinical outcomes in this vulnerable population. Case Description: Herein, we report the case of a 6-year-old patient with significant developmental delay and severe AAI that was successfully managed by stabilization with guidance of neurophysiologic investigations in the perioperative phase. Conclusion: Perioperative neurophysiologic monitoring is safe, useful, and reliable in pediatric patients with trisomy 21 undergoing cervical traction and occipitocervical instrumented fusion for AAI.

Advances in Intraoperative Neurophysiology During Microvascular Decompression Surgery for Hemifacial Spasm.

Microvascular decompression (MVD) is a widely used surgical intervention to relieve the abnormal compression of a facial nerve caused by an artery or vein that results in hemifacial spasm (HFS). Various intraoperative neurophysiologic monitoring (ION) and mapping methodologies have been used since the 1980s, including brainstem auditory evoked potentials, lateral-spread responses, Z-L responses, facial corticobulbar motor evoked potentials, and blink reflexes. These methods have been applied to detect neuronal damage, to optimize the successful decompression of a facial nerve, to predict clinical outcomes, and to identify changes in the excitability of a facial nerve and its nucleus during MVD. This has resulted in multiple studies continuously investigating the clinical application of ION during MVD in patients with HFS. In this study we aimed to review the specific advances in methodologies and clinical research related to ION techniques used in MVD surgery for HFS over the last decade. These advances have enabled clinicians to improve the efficacy and surgical outcomes of MVD, and they provide deeper insight into the pathophysiology of the disease.

Neurophysiology during peripheral nerve surgery.

Electrophysiological monitoring of the peripheral nervous system during a variety of surgeries provides useful information that supplements and complements preoperative assessment. Monitoring improves localization and understanding of the underlying pathophysiology of peripheral nerve lesions leading to more rational treatment decisions and improved outcomes. Monitoring is accomplished by adaptation of routine electrodiagnostic techniques (i.e., nerve conduction studies, evoked potentials, and electromyography) with special attention to technical factors including electrical and movement artifact. These techniques have been successfully applied during surgery for entrapment neuropathies, traumatic nerve injury and repair, peripheral nerve tumors, and adjacent structure procedures that risk peripheral nerve injury. A clear understanding of the anatomy and neurophysiology is necessary, as is understanding and performing the difficult technical aspects of these studies to provide accurate information to enhance patient outcome and recovery. As in any intraoperative neurophysiologic monitoring (IONM) setting, constant and accurate communication between the IONM team, surgeon, and anesthesia team is critically important to meet these goals.

Monitoring surgery around the cranial nerves.

Intraoperative neurophysiologic monitoring (IONM) of cranial nerve (CN) function is an essential component in multimodality monitoring of surgical procedures where CNs are at risk for injury. In most cases, IONM consists of localizing and mapping CNs and their pathways, and monitoring of CN motor function during surgery. However, CN VIII, which has no motor function, and is at risk for injury in many surgical procedures, can be easily and accurately monitored using brainstem auditory evoked potentials. For motor CNs, the literature is clear that function can be safely and adequately performed using basic electromyographic (EMG) techniques, such as recording of continuous EMG activity and electrically evoked compound muscle actions potentials. Newer techniques, such as corticobulbar motor evoked potentials and reflex studies, show good potential for a greater degree of functional assessment but require further study to determine their clinical utility. EMG remains the basic clinical neurophysiologic technique with the greatest clinical research supporting its utility in IONM of motor CN function and should be used as part of a comprehensive multimodality IONM protocol. Understanding the physiologic basis of EMG and the changes associated with altered motor function will allow the practitioner to alter surgical course to prevent injury and improve patient safety.

Evaluation of multimodal intraoperative neurophysiologic monitoring during supratentorial aneurysm surgery: a comparative study.

The objective of this study is to determine the role of multimodal intraoperative neurophysiologic monitoring (IONM) in the overall outcome of intracranial aneurysms surgery, and the risk factors associated with ischemic complications. We grouped 268 ruptured and unruptured intracranial aneurysms surgically treated at our institution into 2 cohorts, based on the use of IONM (180; 67.16%) or non-use of IONM (88; 32.84%). The IONM technique used was multimodal: electroencephalogram (EEG), somatosensory evoked potentials (SSEPs), transcranial (TES), and direct cortical (DCS) stimulation motor evoked potentials (MEPs). There was a significant difference, with a reduction in perioperative strokes (p = 0.011) and better motor surgery-related outcome in the IONM group (p = 0.016). Independent risk factors identified for surgery ischemic complications were temporary clipping time ≥ 6'05″ (odds ratio [OR]: 3.03; 95% CI: 1.068-8.601; p = 0.037), aneurysm size ≥ 7.5 mm (OR: 2.65; 95% CI: 1.127-6.235; p = 0.026), and non-use of IONM (OR: 2.79; 95% CI: 1.171-6.636; p = 0.021). Conversely, aneurysm rupture was not detected as an independent risk factor (OR: 2.5; 95% CI: 0.55-4.55; p = 0.4). Longer temporary clipping time, larger aneurysm size, and the non-use of IONM could be considered as risk factors for ischemic complications during microsurgical clipping. A standardized designed protocol including multimodal IONM with DCS provides continuous information about blood supply and allows reduction of treatment-related morbidity. Multimodal IONM is a valuable technique in intracranial aneurysm surgery.

Intraoperative neurophysiologic monitoring in thoracoabdominal aortic aneurysm surgery can provide real-time feedback for strategic decision making.

OBJECTIVES: Despite the introduction of several adjuncts to improve spinal perfusion, spinal cord ischemia (SCI) remains a devastating complication of thoracoabdominal aortic aneurysm (TAAA) repair. Our aim was to assess the effects on clinical outcome of interventions triggered by motor evoked potentials (MEP) alerts. Furthermore, we want to assess whether a multimodal intraoperative neurophysiologic monitoring (IONM) protocol is helpful for stratifying patients according to the risk of SCI at the end of the vascular phase of surgery. METHODS: We prospectively studied one-hundred consecutive patients who underwent TAAA repair. We applied a multimodal IONM including MEP, somatosensory evoked potentials (SEP) and peripheral nerve monitoring techniques. Signal deteriorations were classified as reversible/irreversible according to whether they recovered or not at the end of monitoring (EOM), set at the end of the vascular phase of surgery. Significant MEP changes drove a series of corrective measures aimed to improve spinal perfusion. RESULTS: The rate of immediate postoperative motor deficits consistent with SCI was significantly higher with irreversible MEP deteriorations compared to reversible ones. The interpretation of MEP findings at the EOM led to the development of risk categories for SCI, based on the association between MEP results and motor outcome. CONCLUSIONS: Our data seem to justify interventions made to reverse MEP deterioration in order to improve the clinical outcome. A multimodal IONM protocol could improve MEP interpretation at the end of the vascular phase of surgery, supporting the surgeon in their decision-making, before concluding vascular maneuvers.

Efficacy of evoked potential monitoring for predicting postoperative motor status in internal carotid artery aneurysm surgeries.

This study aimed to investigate the efficacy of intraoperative motor evoked potential (MEP) and somatosensory evoked potential (SSEP) monitoring for predicting postoperative motor deficits (PMDs) in patients with internal carotid artery (ICA) aneurysms. The data for 138 patients with ICA aneurysms who underwent surgical clipping as well as their intraoperative neuromonitoring data were retrospectively reviewed. The efficacy of MEP/SSEP changes for predicting PMDs was assessed using binary logistic regression analysis. Subsequently, receiver operating characteristic curve analysis was used to obtain a supplementary critical value of the MEP/SSEP deterioration duration. The sensitivity and specificity of MEP changes for predicting PMDs were 0.824 and 0.843, respectively. For SSEP changes, the sensitivity and specificity were 0.529 and 0.959, respectively. MEP and SSEP changes were identified as independent predictors for short-term (p = 0.002 and 0.011, respectively) and long-term PMDs (p = 0.040 and 0.006, respectively). The supplementary critical value for MEP deterioration duration for predicting PMDs was 14 min (p = 0.007, AUC = 0.805). For SSEP, the value was 14.5 min (p = 0.042, AUC = 0.875). The MEP/SSEP changes adjusted by those optimal values were also identified as independent predictors for short-term (p < 0.001 and p = 0.005, respectively) and long-term PMDs (p = 0.019 and 0.003, respectively). Intraoperative MEP and SSEP deterioration durations are effective in predicting PMDs in patients with ICA aneurysms.