Acoustic neuroma neurophysiologic correlates: facial and recurrent laryngeal nerves before, during, and after surgery

This article focuses on the facial nerve with additional comments on the recurrent laryngeal nerve as a proxy for the lower cranial nerves. Methods, advantages and disadvantages, and techniques are listed. The article addresses the anatomy of the facial nerve, discusses neurophysiologic testing, the role of electroneurography in preoperative, intraoperative, and postoperative testing, and presents 7 steps to set up for and perform facial nerve monitoring. Details are provided on interpretation of testing, and the pitfalls of interpretation are discussed. Studies are reviewed presenting outcomes of testing.     

Cerebellopontine angle surgery. Part 2: Specific remarks

OBJECTIVES: Cerebellopontine angle tumors are uncommon lesions that can potentially be cured by microsurgical removal. The primary objective of the surgical treatment differs between vestibular schwannoma and meningioma. This feature may be influenced by the site of tumor origin and displacement of neurovascular structures as well as by their different tumor biology. METHODS: A review of the current literature was conducted. RESULTS AND CONCLUSIONS: Relevant cranial nerves and vascular involvement as well as anatomical location with respect to the cerebellopontine angle are discussed for vestibular schwannoma and meningioma. The main factors influencing the surgical outcome are outlined with special reference to facial and cochlear nerve function and cerebrospinal fluid leakage. The retrosigmoid approach offers a comparable success rate for hearing conservation and probably a superior outcome in terms of facial nerve function when compared with the middle fossa approach. The intrameatal limitations of the retrosigmoid approach can be excluded by the intraoperative assistance of an endoscope. The advantages of endoscope-assisted surgery may include improved visualization of relevant structures, more complete tumor removal, and a lowered risk of cerebrospinal fluid leakage.     

Monitoring of neurophysiologic modalities during surgery for cerebellopontine angle tumors. Personal experiments

The purpose of intraoperative monitoring of many modalities is to save some structures of the nervous system being at risk of damaging during surgical procedures. In cerebellopontine angle (cpa) tumour cases these nervous system structures can include cranial nerves (trigeminal, facial, cochlear, accessory), motor and sensory tracts localised within brainstem, and other. Continuous registration of somatosensory and auditory evoked potentials as well as electromyography of masseter muscle, orbicular muscle of eye and trapezius muscle during procedure is the method of brainstem, cochlear tract and cranial nerves status evaluation. Direct stimulation of cranial nerves within posterior fossa using bipolar electrode is the method of facial, trigeminal and accessory nerves localisation, especially in patients with large tumours. In Department of Neurosurgery Silesian University School of Medicine for intraoperative monitoring of many modalities in cpa lesion cases Nocolet Viking IV D unit with special IOM software is employed. Authors presented own experience in such method and effect in treatment of group of 15 patients operated with electrophysiological intraoperative monitoring.     

Intraoperative electrophysiologic monitoring of laryngeal muscle during thyroid surgery

A technique is described for intraoperative electrophysiologic monitoring of laryngeal muscles. This technique has been used to identify the laryngeal nerves during surgery for recurrent tumors of the thyroid gland, when direct visualization of the nerves is difficult or impossible. Laryngeal muscle electrical activity is monitored with endoscopically placed wire-hook electrodes inserted into the vocal folds bilaterally. Neurotonic discharges are detected when the recurrent laryngeal nerves are manipulated during surgical dissection. Precise localization of the recurrent nerves is possible using a hand-held bipolar stimulator.     

Neuromonitoring—Funktionssicherung und -erhalt bei schädelbasischirurgischen Eingriffen?

BACKGROUND: Neurophysiologic intraoperative monitoring (NIM) has gone through a renaissance since the advent of computer technology. Currently, both motor and sensory cranial nerves, including the IInd and VIIIth cranial nerves, can be intraoperatively controlled by means of small and mobile systems. PATIENTS AND METHODS: In order to estimate the value of NIM using the new generation of computer systems, we analyzed the records of 379 patients who underwent skull base surgery since 1996. These comprised NIM of the IInd, VIIth, VIIIth cranial nerves in most cases and of the IXth, Xth, XIth, and XIIth cranial nerves in selected cases. RESULTS: Whereas 72% of these cases demonstrated changes in the recorded intraoperative NIM signals, only 29% of them gave evidence of either clinical or electrophysiological neural function alterations during the postoperative follow-up. CONCLUSIONS: NIM is the only available system capable of providing the surgeon with instant intraoperative neural status-related feedback.     

Neural conservation in skull base surgery

Surgical treatment of lesions of the skull base carries significant risk to the functioning of the cerebral hemispheres, the brain stem and the cranial nerves. This risk is due both, to problems associated with maintaining an adequate blood flow while exposing and removing the tumor and to direct or indirect trauma to the brain, perineural tissues and cranial nerves. These risks may be reduced if information about possible implications of surgical maneuvers on the cerebral blood flow and on the function of the patients central nervous system and cranial nerves is available and can be monitored during surgery of the skull base. The use of electromyographic neuromonitoring for the facial nerve and of BERA-monitoring for the auditory nerve have been described and are now standard methods to achieve these goals. In acoustic tumors in the last several years beside preservation of the function of the facial nerve hearing preservation especially in small tumors has been one of the primary goals in acoustic neuroma surgery. Computer assisted surgery and intraoperative imaging for lateral skull base surgery are still in their infancy but promise to allow further improvement of neural conservation.     

经鼻内镜手术治疗颅底脊索瘤

脊索瘤是一种起源于胚胎发育时期残留脊索组织的先天性低恶性肿瘤，多发生于骶尾部及颅底中线部位，尤其是斜坡区域，其预后与肿瘤切除程度密切相关，肿瘤完全切除的患者多能长期生存。由于颅底脊索瘤多呈浸润性生长，侵袭范围广，累及颅底重要神经、血管及脑组织等，手术完全切除极其困难，因此被认为是神经外科治疗的难题之一。近年来随着神经内镜技术的发展，以及术中神经导航系统、电生理监测、经鼻超声系统和多普勒超声血管探测仪等监测技术的广泛应用，经鼻内镜入路能在直视下最大可能地安全切除颅底脊索瘤，并尽可能保留重要神经、血管功能，其手术创伤小，术后脑脊液漏等并发症发生率低，并且患者生存质量明显提高，已成为颅底脊索瘤手术治疗的首选方法。为进一步全面认识经鼻内镜治疗颅底脊索瘤的疗效及优缺点，我们查阅了近年来国内外公开发表关于经鼻内镜手术治疗颅底脊索瘤的相关文献，并从术前肿瘤评估分型、手术策略、肿瘤手术切除程度及其影响因素以及术后并发症等几方面对其进行综述。     

Multichannel electrical stimulation of the auditory nerve in man. II. Channel interaction

A multichannel cochlear implant can be an effective prosthesis only if its channels are independent of each other. Presumably independence is achieved by stimulating different populations of surviving neurons. Two types of interaction might occur between channels: electrical current field summation peripheral to stimulation of the nerves and neural-perceptual interaction following stimulation. Two psychophysical techniques to assess channel independence are discussed. In one technique a masker is presented on one channel in order to adapt the nerves responding to that channel. The forward masked threshold of a signal is then measured on all other channels and elevation of threshold is assumed to indicate overlapping neural populations. In the second procedure channel interaction is evaluated by measuring the loudness summation of stimuli presented simultaneously to two channels. The magnitude, distribution, and phasic components of the loudness summation are measures of interaction between channels. Data from two subjects suggests that monopolar stimulation produces broader interaction patterns than bipolar stimulation as a function of electrode separation. Considerable differences in the extent of channel interaction were observed between the two subjects, possibly because of the difference in the absolute current levels needed for equivalent sensation levels.     

Intraoperative Identification of Laryngeal Nerves With Laryngeal Electromyography

The laryngeal nerves are at risk during thyroid surgery, and several techniques have been described for their intraoperative identification to minimize potential damage. Nerve protection is based on the electromyographic recording from the muscles innervated by the laryngeal nerves, and that electrical activity is picked up by various techniques. We evaluated an electrode attachment to the endotracheal tube that provides a stable method for continuous recording of the laryngeal electromyogram. In addition, we tested various modalities of electrical stimulation in the region where the nerves are located, identified the most reliable evoked electromyographic activity, and characterized the wave form and latency. The results, obtained in 28 patients scheduled for thyroid and parathyroid surgery, indicate that the technique of recording from electrodes attached to the endotracheal tube is safe and reliable. Insulated bipolar forceps or a monopolar electrode was used to deliver low-voltage pulses (1 to 3 V) at 1 to 2 pulses/s generated by either battery-operated or optically isolated stimulators. The most unequivocal recordings were obtained with the monitoring equipment set to the nerve-conduction velocity modality, with the sweep set at 2 msec/cm. The technique clearly differentiated the evoked electromyographic responses obtained from the superior or recurrent laryngeal nerve and was easily performed with no perioperative complications.     

鞍结节脑膜瘤的手术治疗

目的 探讨鞍结节脑膜瘤手术治疗的入路选择及术中注意要点。方法 选择５４例鞍结节脑膜瘤,根据肿瘤的直径（以３ｃｍ为界）和其发展的方向分别采用单侧额下入路、双侧额下入路与冀点入路进行手术治疗。结果 ２２例单侧额下入路组肿瘤全切除率为８３％;２６例双侧额下入路组全切除率７７％,双侧嗅神经损伤１例,因下丘脑损伤死亡１例;６例冀点入路组全切除率６７％,１例因颈动脉损伤而死亡。结论 应根据肿瘤的大小而选择相应     

Minimal-access parathyroid surgery using intraoperative parathyroid hormone assay

Objectives: Review the most current preoperative localization imaging techniques in patients with primary hyperparathyroidism and demonstrate their applicability to targeted tumor removal with intraoperative parathyroid hormone (PTH) monitoring. Study Design: Retrospective review of 40 consecutive patients undergoing parathyroid surgery with intraoperative PTH assay as the principal determinant of correction of the hyperparathyroid state. Details of the technology, cost analysis, and comparison with other management methods are discussed. Methods: The standard intact PTH chemiluminescent assay (Nichols Diagnostics) and modifications to allow accelerated intraoperative results are discussed in detail. The time intervals between completion of parathyroid excision and postremoval assay and subsequent laboratory investigation present a practical therapeutic algorithm. Results: Forty consecutive patients with hyperparathyroidism were treated surgically with intraoperative PTH as the determinant of satisfactory resolution of the disease state. In most instances, the surgical field was reduced to the targeted pathology identified by preoperative localization, and all patients became eucalcemic when this method was employed. Approximately half of eligible patients were treated under local anesthesia. Conclusions: Intraoperative PTH assay has added a new dimension to primary and revision parathyroid surgery. It is cost-effective and accurate and may reduce the morbidity of surgical intervention in revision procedures. Laryngoscope, 108:1497–1503, 1998     

Laryngeal reinnervation

Laryngeal reinnervation refers to any of a number of surgical procedures intended to restore neural connections to the larynx, which have usually been lost from some type of trauma (eg, surgical).The nerve function(s) to be restored may be those of the recurrent laryngeal nerve or its subdivisions, those of the superior laryngeal nerve, or both, and they may be motor or sensory. Several different donor nerves are available and have been described. The technique used may be direct end-to-end anastomosis (neurorrhaphy), direct implantation of a nerve ending into a muscle, the nerve-muscle pedicle technique, or muscle-nerve-muscle methods. These nerves and techniques may be combined in many ways. A number of new techniques have been reported in animal studies; however, the animal studies do not always predict the results of analogous surgeries in human patients. The historical and current perspectives on these techniques are discussed in this article.     

Current aspects of radiotherapy of glomus jugulare tumors

Small glomus jugulare tumors can be operated on successfully. The intraoperative risk of bleeding may be reduced by preoperative irradiation or angiographic embolisation. Patients with advanced tumors (bone destruction, paralysis or cranial nerves and/or invasion of brain) are at high risk if they are operated on. In these cases radiotherapy is an effective alternative with a fairly low complication rate. Prerequisites for successful irradiation are assessment of treatment volume and treatment planning by CT, sophisticated stereotactic irradiation techniques, application of high energy photons and reliable immobilisation measures. Furthermore it is possible to deliver higher doses, leading to regression of the tumor and its symptoms. The technique is illustrated by two characteristic cases. Although irradiation alone can achieve tumor remission the long term prognosis remains doubtful.     

Recurrent laryngeal nerve monitoring in thyroid and parathyroid surgery: the University of Michigan experience

OBJECTIVES/HYPOTHESIS: Intraoperative monitoring of the recurrent laryngeal nerve (RLN) is finding increasing acceptance during thyroidectomy. Recently, a laryngeal surface electrode was introduced to enable another form of noninvasive monitoring of the RLN. The present report examines the University of Michigan experience with RLN monitoring using the postcricoid surface electrode. STUDY DESIGN: All patients undergoing partial or total thyroidectomy or parathyroidectomy from January 1999 to July 2001 were considered candidates for the study. Audiologists trained in intraoperative electrophysiological techniques performed all of the monitoring. METHODS: Data collected on each patient included 1) stimulation threshold for a laryngeal compound muscle action potential on initial RLN identification, 2) stimulation threshold of the laryngeal compound muscle action potential on completion of the procedure, and 3) flexible fiberoptic evaluation of the larynx at the initial postoperative visit and at the 3-month follow-up visit. The average duration of follow-up was 9.8 months with a range of 3 to 60 months. RESULTS: The average minimum current required for stimulation on first identification of all nerves was 0.57 mA (+/-0.48 mA). After completion of the procedure a mean threshold level of 0.42 mA (+/-0.55 mA) was obtained during direct RLN stimulation. Post-dissection stimulation of the RLN on the side of tumor dissection was 0.92 mA (+/-0.65 mA) compared with a stimulation threshold of 0.76 mA (+/-0.57 mA) for the nontumor side. CONCLUSIONS: Electromyographic monitoring of the RLN using a postcricoid surface electrode provides a safe, simple, and effective method for intraoperative monitoring during thyroid or parathyroid surgery. Further, evoked electromyography confirms RLN integrity at the conclusion of surgery.     

Detecting and identifying nonrecurrent laryngeal nerve with the application of intraoperative neuromonitoring during thyroid and parathyroid operation

Purpose

The nonrecurrent laryngeal nerve (NRLN) is a rare anatomical variant but associated with high risk of nerve injury during thyroid and parathyroid operations. Therefore, intraoperative detection and verification of NRLN are necessary.

Method

A total of 390 consecutive patients who underwent thyroid and parathyroid operations (310 RLNs dissected on the right side and 293 nerves on the left side) were enrolled. Electrically evoked electromyography was recorded from the vocalis muscles via an endotracheal tube with glottis surface recording electrodes. At an early stage of operation, vagal nerve was routinely stimulated at the level of inferior thyroid pole to ensure normal path of RLN. If there is a negative response from lower position but positive response from upper vagal stimulation, it indicates the occurrence of a NRLN, and we localize its separation point and path.

Results

Four right NRLNs (1.3%) without preoperative recognition were successfully detected at an early stage of operation. Three patients were operated on for thyroid disease, one for parathyroid adenoma and all were associated with right aberrant subclavian artery. All NRLNs were localized and identified precisely with intraoperative neuromonitoring. Functional integrity of all nerves was confirmed by the intraoperative neuromonitoring and postoperative laryngeal examination.

Conclusions

Vagal stimulation at the early stage of operation is a simple, useful, and reliable procedure to detect and identify the NRLN.     

Laryngeal adductor reflex hyperexcitability may predict permanent vocal fold paralysis

Laryngeal adductor reflex–continuous intraoperative neuromonitoring (LAR-CIONM) is a novel method of continuous intraoperative neuromonitoring. In contrast to other vagal nerve monitoring techniques, which elicit a laryngeal compound muscle action potential, LAR-CIONM elicits a laryngeal reflex response (LAR). In 300 nerves at risk monitored with LAR-CIONM, two patients have had postoperative permanent vocal fold immobility (VFI). Both patients exhibited a significant LAR amplitude increase prior to complete loss of signal. No other patients have exhibited LAR hyperexcitability. If confirmed in a larger sample, this represents the first time that a vagal intraoperative neuromonitoring technique can distinguish transient from permanent VFI, which could improve patient outcomes. Laryngoscope, 2019 Laryngoscope, 130:E625–E627, 2020     

Intraoperative identification of regenerated chorda tympani nerve and its relationship to recovered taste function.

This study demonstrated a simple method of repairing the severed chorda tympani nerve and a method of intraoperative identification of regenerated nerves, and evaluated taste function of regenerated nerves. Seven patients who underwent staged tympanoplasty and whose chorda tympani nerve was severed during primary surgery were evaluated. When the chorda tympani nerve was severed during primary surgery, proximal and distal stumps were anastomosed or approximated almost in the original position and fixed with fibrin glue on the temporal muscle fascia used to reconstruct the eardrum by the underlay method. During primary surgery, end-to-end anastomosis was possible in 3 patients but nerve gap defects remained in the other 4 patients. In all 7 patients, regenerated nerves were identified during secondary surgery not in the tympanic cavity but in the submucosal layer of the previously reconstructed eardrum. In all patients, complete or incomplete recovery of taste perception was observed by both the filter paper disk method and electrogustometry, suggesting that the regenerated nerves had actual taste function. From these results, it was concluded that the severed chorda tympani nerve could regenerate in the reconstructed eardrum even if nerve gap defects remained between the proximal and distal cut ends, when repair or approximation of the nerve was properly completed.     

Cochleovestibular nerve compression syndrome. II. Vestibular nerve histopathology and theory of pathophysiology.

The present study was undertaken to systematically examine and characterize pathological changes in vestibular nerve specimens obtained at surgery in patients with symptomatic cochleovestibular nerve compression syndrome (CNCS). Vestibular nerves were obtained in six cases of CNCS and were intermingled with vestibular nerves obtained in cases of Meniere's disease. All of the nerve specimens were coded and reviewed microscopically in a blind-study fashion by the neuropathologist. The vestibular nerves obtained from CNCS cases showed significant endoneurial fibrosis, compared to controls (specimens from patients with Meniere's disease). Based on observations in this study, as well as the clinical symptoms and audiovestibular test findings in these patients, a theory of pathophysiology in CNCS of the cochleovestibular nerve is proposed. The implications of this theory are discussed with respect to the diagnosis of CNCS.     

甲状腺乳头状癌累及喉返神经的处理方法

 目的探讨甲状腺乳头状癌累及喉返神经的处理方法。方法根据42例甲状腺乳头状癌侵犯喉返神经情况分为包绕、黏连、压迫3组,术中根据喉返神经与肿瘤的关系结合术前声带运动情况综合考虑是否保留喉返神经。包绕组无论声带活动情况如何,喉返神经均予切除。黏连组如伴完全声带麻痹,切除喉返神经;否则喉返神经予以保留。压迫组喉返神经均予保留。观察所有患者声带术后活动情况、评估疗效。结果42例患者中甲状腺全切除23例,次全切除术19例,随访1年术后均未复发。包绕组患者均行喉返神经切除,术后声带完全麻痹;粘连组中,3例声带完全麻痹者切除喉返神经、术后声带完全麻痹,9例术前不完全声带麻痹均予以保留喉返神经,2例术后出现声带完全麻痹,3例声带不完全麻痹,4例声带运动恢复正常;压迫组无声带完全麻痹,完整保留喉返神经,术后声带运动均恢复正常。结论对甲状腺乳头状癌侵犯喉返神经的处理,应结合术前声带运动情况及术中喉返神经与肿瘤关系采取不同的处理方法。     

Electrophysiologic laryngeal nerve monitoring in high-risk thyroid surgery

We recently began performing intraoperative electrophysiologic monitoring of the recurrent laryngeal nerve and the external branch of the superior laryngeal nerve during high-risk thyroidectomies. Neuromonitoring can detect stimulation of these nerves and thereby prevent a mechanical or thermal injury that can result in neurapraxia or axonotmesis. Monitoring is also useful during dissection in an already operated-on field, when performing thyroidectomy on patients who depend on their voice for their livelihood, and when removing a large goiter or mediastinal mass.