Continuous intraoperative neuromonitoring (cIONM) in head and neck surgery-a review

History of Clinical Neurophysiology in Mexico

SUMMARY

In the 18th century, Luigi Galvani proposed the hypothesis of animal electricity, which is produced by the brain and distributed through the nerves to the muscles. This was the cornerstone of what is known today as the modern study of nerve function, earning him the title of the Father of Clinical Neurophysiology. The 19th century was subsequently marked by two major figures: Santiago Ramón y Cajal (Neuron Theory) and Hans Berger, known for describing cerebral electrical activity and recording the first electroencephalograms. In Mexico, Clinical Neurophysiology emerged in the late 19th century and consolidated itself in the first half of the 20th century. In the year of 1938, Dr. Clemente Robles and Teodoro Flores Covarrubias built the first electroencephalograph, marking the beginning of the era of Clinical Neurophysiology. Initially, this diagnostic tool was primarily applied to psychiatric patients, as there was no clear separation between psychiatry and neurology and patients were treated jointly at the largest psychiatric center of that time, "La Castañeda." In 1968, the Mexican Society of Electroencephalography A.C. was founded and later changed its name to the Mexican Society of Clinical Neurophysiology A.C. Simultaneously, its members achieved universal recognition of the medical specialty, which has become established in clinical practice and has shown progressive academic and scientific growth in Mexico.

Paradigms of intraoperative neuromonitoring in paediatric thyroid surgery

The larynx of children and adolescents is still in the developmental phase and the anatomical structure is still very small and sensitive. The higher malignancy and faster progression of some paediatric thyroid cancers make surgery more difficult. Intraoperative neuromonitoring (IONM) is frequently used in thyroid surgery as an effective means of securing the recurrent laryngeal nerve (RLN). Little information is available on the clinical efficacy of IONM in paediatric surgery. In addition, classic IONM techniques such as reinforced tracheal tube models with integrated surface electrodes are not standardised for children and adolescents. The use of innovative devices such as laryngeal masks with surface electrodes and thyroid cartilage receiving electrodes could replace monitoring tubes as a new form of IONM. Tracheal intubation in children needs to be performed by a highly experienced anaesthetist. The continued maturation of AI technology could be attempted in the future in conjunction with IONM to further reduce RLN injuries in children and adolescents. This article describes the anatomical features of the paediatric larynx, which differ from those of adults, and the advantages and shortcomings of IONM techniques for thyroid surgery in this population. The use of IONM in paediatric surgery is a complex technique and should be performed by experienced thyroid surgeons with in-depth IONM training. The use of IONM should be standardised within the clinical parameters of children.

Novel continuous and quantitative intraoperative facial nerve-monitoring system for temporal bone lesions

OBJECTIVE

Intraoperative systems for monitoring facial nerve function, in which temporal electrical stimulation is applied to the facial nerve through electrodes, are used in many surgeries requiring facial nerve preservation; however, continuous stimulation or quantitative evaluation of facial nerve function is difficult with this approach. We examined the usefulness of a continuous and quantitative facial nerve-monitoring system for temporal bone lesions by using our experience to modify the existing methods used for cases involving vestibular schwannomas.

STUDY DESIGN

Retrospective observational study.

SETTING

Department of Otorhinolaryngology-Head and Neck Surgery at our hospital.

METHODS

We modified the electrode placement and examined the usefulness of the modified system under several conditions. The study population consisted of patients who were operated on for temporal bone lesions at our department and underwent continuous nerve monitoring using the modified system. Case details, electrode-placement sites, and facial nerve function data before and after the surgery were obtained and retrospectively evaluated.

RESULTS

Electrodes were placed safely during surgery in all cases. No obvious deterioration in facial nerve function was observed, except in one case.

CONCLUSION

The advantages of this system include its ability to perform quantitative intraoperative evaluations and prevent unexpected nerve damage in cases where the facial nerve shows complicated pathways. This monitoring system is useful, even in complex temporal bone surgeries.

State of the art of neuromonitoring in thyroid surgery

Thyroidectomy is a common procedure in endocrine surgery, frequently performed to treat benign and malignant thyroid conditions. Recurrent laryngeal nerve (RLN) injury, a major complication, underscores the necessity for meticulous nerve dissection during surgery. Intraoperative neuromonitoring (IONM) has emerged as a valuable adjunct to visual identification in RLN preservation. This review synthesizes current literature on IONM in thyroid surgery, emphasizing its role in enhancing RLN integrity assessment and reducing surgical complications such as vocal cord paralysis. IONM techniques include intermittent and continuous monitoring, each offering distinct benefits in nerve function evaluation. While debate persists regarding IONM's efficacy in mitigating unilateral RLN injuries, protocols integrating IONM data have significantly reduced the incidence of bilateral RLN injury, exemplifying advancements in surgical safety. Challenges remain, including variability in study outcomes and the optimal timing of IONM application.

Comprehensive Mapping and Dynamic Monitoring of the Temporal Branch of the Facial Nerve in Complex Cranial Reconstruction Surgery and Revision Cranioplasty

Facial nerve (FN) injury is a significant risk during complex cranial reconstruction surgeries, especially in revision cases where normal anatomy is distorted. The authors introduce a technique to mitigate FN injury, including preoperative FN mapping, intraoperative FN mapping, and continuous FN monitoring. Preoperative mapping uses a handheld ball-tip stimulator to elicit compound muscle action potentials (CMAP) in the frontalis muscle. Needle electrodes are placed above the orbital margin to record responses, starting at the stylomastoid foramen and extending until the entire temporal branch is mapped. Intraoperatively, continuous mapping is achieved using an electrified insulated suction device, allowing dynamic mapping during soft tissue dissection. Continuous monitoring involves placing stimulation electrodes near the stylomastoid foramen and recording CMAP responses from the frontalis and orbicularis oculi/orbicularis oris muscles. The authors tested this technique in 5 patients. The authors successfully mapped the temporal branch of the FN with isolated frontalis CMAP recordings in all patients. Intraoperative FN mapping and continuous monitoring were successfully performed in all cases. Two patients experienced complete cessation of FN CMAPs, which resumed upon loosening the tension on the myocutaneous flap held by fishhooks. One patient showed a 39% decrement in frontalis CMAP that did not recover. Despite these issues, all patients had intact FN function postoperatively and at follow-up. Our technique shows promise in mitigating FN injury during complex cranial reconstruction and cranioplasty revision surgery. Further research with a larger cohort is needed to confirm efficacy and statistical significance.

A Rare Case of Sublingual Lipoma

Lipomas are benign soft tissue tumors that are ubiquitous in nature. Available literature suggests that benign tumors are harmless unless they increase in size, resulting in compression of vital structures. This case report discusses the case of a 52-year-old man who presented to the clinic with a painless, growing lump on the right side of his mouth. The patient's symptoms included difficulty swallowing and speaking, which led the doctors to recommend surgical excision of the mass. There were no issues during the mass removal surgery, and the incision healed without compromising the lingual or hypoglossal nerves or Wharton's duct, as observed during follow-up visits. Patient history, symptoms, preoperative examination, treatment strategy, and surgical technique are all included in this case study, which focuses on the extremely unusual development of lipomas in the oral cavity, particularly on the floor of the mouth.

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

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

The weepy cry - short neural signal bursts in intraoperative neuromonitoring

PURPOSE

This study aimed to establish an in-vitro alternative to existing in-vivo systems to analyze nerve dysfunction using continuous neuromonitoring (C-IONM).

METHODS

Three hundred sixty-three recurrent laryngeal nerves (RLN) (N(pigs) = 304, N(cattle) = 59) from food industry cadavers were exposed by microsurgical dissection following euthanasia. After rinsing with Ringer's lactate, they were tempered at 22 °C. Signal evaluation using C-IONM was performed for 10 min at 2 min intervals, and traction forces of up to 2N were applied for a median time of 60 s. Based on their post-traumatic electrophysiological response, RLNs were classified into four groups: Group A: Amplitude ≥ 100%, Group B: loss of function (LOS) 0-25%, Group C: ≥ 25-50%, and Group D: > 50%.

RESULTS

A viable in-vitro neuromonitoring system was established. The median post-traumatic amplitudes were 112%, 88%, 59%, and 9% in groups A, B, C, and D, respectively. A time-dependent further dynamic LOS was observed during the 10 min after cessation of strain. Surprisingly, following initial post-traumatic hyperconductivity, complete LOS occurred in up to 20% of the nerves in group A. The critical threshold for triggering LOS was 2N in all four groups, resulting in immediate paralysis of up to 51.4% of the nerves studied.

CONCLUSION

Consistent with in-vivo studies, RLN exhibit significant intrinsic electrophysiological variability in response to tensile forces. Moreover, nerve damage progresses even after the complete cessation of strain. Up to 20% of nerves with transiently increased post-traumatic amplitudes above 100% developed complete LOS, which we termed the "weepy cry." This time-delayed response must be considered during the interpretation of C-IONM signals.

Continuous intraoperative neuromonitoring of the facial nerve predicts postoperative facial palsy in parotid surgery: a prospective study

PURPOSE

Facial palsy (FP) is the most significant complication of parotidectomy. Currently, the use of intermittent intraoperative neuromonitoring (iIONM) in parotid surgery facilitates nerve detection, which is paramount to nerve protection. Continuous IONM (cIONM), as applied in thyroid surgery, enables real-time information on electrophysiological nerve status through continuous nerve stimulation, thereby allowing consequent amplitude analysis. To date, the application of cIONM in parotid surgery has not been noted in literature.

METHODS

We performed parotidectomies with anterograde facial nerve visualization using cIONM in 32 consecutive patients in a prospective study (German Register of clinical studies-DRKS 00011051) during the period October 2016 to January 2020. After the facial trunk had been exposed, an atraumatic stimulation electrode was placed and the nerve was stimulated at 3 Hz, at a low threshold (0.62 ± 0.06 mA), for the entire duration of the preparation. Selected electrophysiological parameters were collected and compared to postoperative facial nerve function, measured by the House-Brackmann grading system.

RESULTS

In the post hoc analysis, a significant correlation between a drop in amplitude (< 50% of the "baseline" amplitude) and postoperative FP was recorded (p = 0.001). True positive prediction of FP was noted in 14 out of 16 patients and true negative in 10 out of 16. The sensitivity was 87.5% (AUC 0.75), with a high negative predictive value of 83.3%.

CONCLUSION

cIONM has significant value in predicting postoperative FP in parotidectomy. Future development of an acoustic/optic warning system in IONM devices could prevent nerve injury in real time.

Vagus Nerve Stimulation in the Carotid Triangle: An Effective Method for Monitoring the Recurrent Laryngeal Nerve in Thyroid and Parathyroid Surgery

OBJECTIVE

Our objective is the description of the technique of vagus nerve stimulation in carotid triangle in order to monitor the recurrent laryngeal nerve (RLN) during thyroid and parathyroid surgery.

METHODS

We stimulated the vagus nerve in the carotid triangle during 150 thyroid or parathyroid surgeries using a monopolar electromyography electrode inserted under the mastoid process towards the jugular foramen as a cathode, and using another subdermal electrode in the mastoid as an anode. Another complementary method of vagus stimulation was achieved with a pair of subdermal electrodes, placing the cathode at the mandibular angle and the anode at the mastoid.

RESULTS

In all patients, compound muscle action potential (CMAP) was recorded in the vocal cords with both stimulation techniques, allowing semi-continuous monitoring to be carried out. Intraoperative lesions were detected in 16 of the cases; 9 of them were transient with CMAP recovery achieved when modifying surgical maneuvers.

CONCLUSIONS

Vagus nerve stimulation in the carotid triangle is a reliable technique for monitoring the RLN in thyroid surgery. Vagus nerve stimulation in the carotid triangle is effective and safe for RLN monitoring, and it is a clear alternative to direct continuous stimulation of the nerve that by contrast requires its dissection in the carotid sheath.

Review of Piezoelectrical Materials Potentially Useful for Peripheral Nerve Repair

It has increasingly been recognized that electrical currents play a pivotal role in cell migration and tissue repair, in a process named "galvanotaxis". In this review, we summarize the current evidence supporting the potential benefits of electric stimulation (ES) in the physiology of peripheral nerve repair (PNR). Moreover, we discuss the potential of piezoelectric materials in this context. The use of these materials has deserved great attention, as the movement of the body or of the external environment can be used to power internally the electrical properties of devices used for providing ES or acting as sensory receptors in artificial skin (e-skin). The fact that organic materials sustain spontaneous degradation inside the body means their piezoelectric effect is limited in duration. In the case of PNR, this is not necessarily problematic, as ES is only required during the regeneration period. Arguably, piezoelectric materials have the potential to revolutionize PNR with new biomedical devices that range from scaffolds and nerve-guiding conduits to sensory or efferent components of e-skin. However, much remains to be learned regarding piezoelectric materials, their use in manufacturing of biomedical devices, and their sterilization process, to fine-tune their safe, effective, and predictable in vivo application.

Large Sublingual Lipoma: A Case Report

Lipomas are benign soft tissue tumors frequently observed throughout the body. Lipomas rarely cause health concerns; however, when symptomatic, it is often related to their location and size. A 65-year-old male patient presented with a non-tender, enlarging mass in the anterior floor of the mouth, which was otherwise asymptomatic. Computed tomography evaluation revealed an unusually large hypolucent mass, posterior to the inner table of the right anterior mandible. Surgical excision was uncomplicated. Upon follow-up, the right anterior floor of the mouth wound healed without compromise of the lingual or hypoglossal nerves or Wharton's duct. This discussion highlights the infrequent occurrence of lipomas in the oral cavity, particularly in the floor of the mouth, including patient presentation, preoperative evaluation, and surgical planning.

Frontiers of Cranial Base Surgery: Integrating Technique, Technology, and Teamwork for the Future of Neurosurgery

The landscape of cranial base surgery has undergone monumental transformations over the past several decades. This article serves as a comprehensive survey, detailing both the historical and current techniques and technologies that have propelled this field into an era of unprecedented capabilities and sophistication. In the prologue, we traverse the historical evolution from rudimentary interventions to the state-of-the-art neurosurgical methodologies that define today's practice. Subsequent sections delve into the anatomical complexities of the anterior, middle, and posterior cranial fossa, shedding light on the intricacies that dictate surgical approaches. In a section dedicated to advanced techniques and modalities, we explore cutting-edge evolutions in minimally invasive procedures, pituitary surgery, and cranial base reconstruction. Here, we highlight the seamless integration of endocrinology, biomaterial science, and engineering into neurosurgical craftsmanship. The article emphasizes the paradigm shift towards "Functionally" Guided Surgery facilitated by intraoperative neuromonitoring. We explore its historical origins, current technologies, and its invaluable role in tailoring surgical interventions across diverse pathologies. Additionally, the digital era's contributions to cranial base surgery are examined. This includes breakthroughs in endoscopic technology, robotics, augmented reality, and the potential of machine learning and AI-assisted diagnostic and surgical planning. The discussion extends to radiosurgery and radiotherapy, focusing on the harmonization of precision and efficacy through advanced modalities such as Gamma Knife and CyberKnife. The article also evaluates newer protocols that optimize tumor control while preserving neural structures. In acknowledging the holistic nature of cranial base surgery, we advocate for an interdisciplinary approach. The ecosystem of this surgical field is presented as an amalgamation of various medical disciplines, including neurology, radiology, oncology, and rehabilitation, and is further enriched by insights from patient narratives and quality-of-life metrics. The epilogue contemplates future challenges and opportunities, pinpointing potential breakthroughs in stem cell research, regenerative medicine, and genomic tailoring. Ultimately, the article reaffirms the ethos of continuous learning, global collaboration, and patient-first principles, projecting an optimistic trajectory for the field of cranial base surgery in the coming decade.

Continuous intraoperative neuromonitoring of the recurrent laryngeal nerve during lung operations

Background

The recurrent laryngeal nerve (RLN), especially on the left side, is particularly vulnerable during lung operations. Therefore, continuous intraoperative neuromonitoring (cIONM) would be desirable. With the use of a double-lumen tube (DLT) for single-lung ventilation, there is some uncertainty where the recording electrode should be positioned. The aim of this study was to assess the feasibility of this technique and to predict the ideal position of a single recording electrode.

Methods

Patients scheduled to undergo left thoracotomy due to pulmonary pathologies, two adhesive electrodes were affixed consecutively above the proximal cuff of the DLT prior to intubation for a precise location of the recording from the vocal cords. Following thoracotomy, the vagus nerve alongside the aortic arch was exposed. A continuous stimulation probe (Saxophone® electrode, Dr. Langer Medical, Waldkirch, Germany) was placed around the nerve. The signals of the respective electrode were recorded and analyzed with regard to previously defined limits of positive signaling.

Results

Strong signals with an amplitude of at least 165 µV were recorded in 18 of 20 patients. In these patients 100% of the signals were recorded via the distally located electrode. An additional signal was recorded via the proximal electrode in four patients. cIONM was found to be a safe and reproducible technique.

Conclusions

The described technique enables the use of cIONM of the RLN throughout the entire course of the surgical procedure.

Neural networks for estimation of facial palsy after vestibular schwannoma surgery

PURPOSE

Facial nerve damage in vestibular schwannoma surgery is associated with A-train patterns in free-running EMG, correlating with the degree of postoperative facial palsy. However, anatomy, preoperative functional status, tumor size and occurrence of A-trains clusters, i.e., sudden A-trains in most channels may further contribute. In the presented study, we examine neural networks to estimate postoperative facial function based on such features.

METHODS

Data from 200 consecutive patients were used to train neural feed-forward networks (NN). Estimated and clinical postoperative House and Brackmann (HB) grades were compared. Different input sets were evaluated.

RESULTS

Networks based on traintime, preoperative HB grade and tumor size achieved good estimation of postoperative HB grades (chi2 = 54.8), compared to using tumor size or mean traintime alone (chi2 = 30.6 and 31.9). Separate intermediate nerve or detection of A-train clusters did not improve performance. Removal of A-train cluster traintime improved results (chi2 = 54.8 vs. 51.3) in patients without separate intermediate nerve.

CONCLUSION

NN based on preoperative HB, traintime and tumor size provide good estimations of postoperative HB. The method is amenable to real-time implementation and supports integration of information from different sources. NN could enable multimodal facial nerve monitoring and improve postoperative outcomes.

Intra-operative nerve monitoring and recurrent laryngeal nerve injury during thyroid surgery: a network meta-analysis of prospective studies

PURPOSE

Recurrent laryngeal nerve (RLN) injury is a feared complication of thyroid surgery occurring in 1-5% of cases. The present approaches to RLN preservation include RLN visualization with no nerve monitoring (No-NM), intermittent intra-operative nerve monitoring (I-IONM) and continuous intra-operative nerve monitoring (C-IONM). There is ambiguity as to which of these strategies should be the preferred method of RLN preservation.

METHODS

A systematic review of the PubMed, Embase and the Cochrane Collaboration databases was undertaken with network meta-analysis (NMA) performed according to the PRISMA and Cochrane Collaboration guidelines. A Bayesian NMA was conducted using R packages netmeta with outcomes expressed as odds ratios (ORs) with 95% credible intervals (CrI). Only prospective studies were included.

RESULTS

Eighteen studies met inclusion criteria, including 22,080 patients and 40,642 nerves at risk (NAR). Overall, 23,364 NARs (57.5%) underwent I-IONM, 17,176 (42.3%) No-NM and 98 (0.2%) underwent C-IONM. There were no significant differences between groups regarding the incidence of permanent RLN injury following thyroid surgery (I-IONM vs.No-NM, OR 0.84, 95% CrI 0.55-1.19; C-IONM vs. No-NM, OR 0.44, 95% CrI 0.02-5.00). Pooled analysis showed that IONM (I-IONM or C-IONM) demonstrated a protective effect versus No-NM in reducing the incidence of transient RLN injury (OR 0.75, 95% CI 0.59-0.97, p = 0.03).

CONCLUSIONS

IONM strategies did not significantly reduce the incidence of permanent RLN injury following thyroid surgery. However, the small number of C-IONM NARs limits conclusions that may be drawn. Further well-designed prospective studies will be required to definitively assess the utility of C-IONM.

Preoperative ultrasound mapping of the vagus nerve in thyroid surgery

BACKGROUND

Intraoperative neuromonitoring (IONM) in thyroid surgery requires electric stimulation of the vagus nerve to verify correct electrode placement. Classically the nerve is found deep to or in-between the common carotid artery and internal jugular vein, but previous studies have shown that the nerve can sometimes be found superficial to the vessels. Our aim was to determine the incidence of a superficial vagus nerve using ultrasound (US) and study possible clinical factors associated with an anteriorly-located vagus nerve.

METHODS

Retrospective study of patients undergoing thyroid surgery (lobectomy or total thyroidectomy) with intermittent IONM. Substernal goiters, locally invasive tumors or bulky lymph nodes were excluded. The vagus nerve was identified at the level of the mid-thyroid lobe on each side on preoperative US performed by two specialized radiologists, and its location according to 6 possible positions in relationship to the common carotid artery was recorded. The anatomic variability of the vagus nerve was analyzed in relationship to patient demographics and thyroid pathology.

RESULTS

Five-hundred twenty-seven patients were included. The right vagus nerve (n=522) was in-between, superficial or deep to the vessels in 92.3%, 6.1% and 1.5% and of cases, respectively, and the left vagus (n=517) in 80.2%, 18.6% and 1.2% of cases, respectively, with a statistically significant difference between right and left vagus nerves (P<0.001). The type of pathology, size of the dominant nodule or the volume of the thyroid lobe were not correlated to finding a superficial vagus nerve.

CONCLUSIONS

The vagus nerve was identified in all cases on US and found to be anterior to common carotid artery at the level of the thyroid lobe in 18.6% of cases on the left and 6.1% of cases on the right. Identifying this anatomic variant preoperatively may facilitate IONM and avoid inadvertent trauma to the vagus nerve during thyroid surgery.

Large Lipoma of the Mouth Floor

Lipomas are one of the most common benign connective tissue masses in the human body. They rarely cause issues and are typically removed for cosmetic reasons. They rarely appear in the oral cavity though they are common. Thus, only a few sublingual lipoma cases have been reported. We present a case of a male in his 60s who came to our clinic complaining of dysphagia and dysarthria caused by an oral swelling from a right sublingual simple lipoma. It was decided to be removed surgically under general anesthesia, with neuromonitoring of the right hypoglossal nerve. The patient tolerated the surgery without complications and fully recovered with complete resolution of his mass effect symptoms. This case demonstrated the importance of having a wide differential diagnosis of oral lesions, especially in a patient with a complicated medical history. Though it is not used often, the case also demonstrated the neuroprotective effect of intraoperative hypoglossal nerve monitoring during sublingual surgeries.

A Bibliometric Analysis of Intraoperative Neuromonitoring in Spine Surgery

Intraoperative neuromonitoring (IONM) techniques are usually implemented during spine surgery to avoid nefarious abuse of the nervous system, which can cause postoperative problems. A lack of bibliometric analysis on the topic of IONM in spine surgery has been identified. Therefore, the aims of this study are to provide information about the main contributors to this field and their publication dynamics, as well as conceptual and cooperative networks. Results have shown that a steady publication increase has been occurring since 1991, with high levels of citations in the first decade, but irregular publication rates have been recorded more recently. Research production by country seems to be in line with what is observed in other surgical fields, but research funding for IONM in spine surgery seems to be lower, even with the clear interest of private funding agencies. The conceptual networks have shown the importance of motor-evoked potential, electromyography, and the effect of anesthesia, particularly in scoliosis surgery.