Spontaneous laryngeal reinnervation after recurrent laryngeal or vagus nerve injury

OBJECTIVES: The status of innervation in patients with laryngeal paralysis is somewhat controversial. Electromyographic activity has been frequently documented in the laryngeal muscles of patients with laryngeal paralysis, and animal experiments report a strong propensity for reinnervation after laryngeal nerve injury. However, a study of intraoperative electromyography performed in patients during reinnervation surgery failed to document activity with stimulation of the recurrent laryngeal nerve (RLN). Noting the long-observed differences in the symptoms of patients with vagus nerve injury and those with RLN injury, I hypothesized that reinnervation is influenced by the site of nerve injury. METHODS: Cats were sacrificed at various intervals after resection of 1 cm of either the RLN or the vagus nerve, without any attempt to repair the nerve. RESULTS: Four months after RLN resection, distal nerve biopsy revealed unmyelinated axons scattered through fibrous tissue. By 6 months, myelinated axons were organized, and electromyographic and histologic examination showed preferential reinnervation of the thyroarytenoid muscle. After vagotomy, the RLN was fibrotic and no axons were present. Both the thyroarytenoid and posterior cricoarytenoid muscles were fibrotic and had no electromyographic activity. CONCLUSIONS: The results confirm the strong propensity for laryngeal reinnervation after RLN injury, but not after vagus nerve injury. Preferential reinnervation of adductor muscles may account for a medial position of the paralyzed vocal fold.     

Airway complications in the head injured

Fifty head-injured patients who had tracheostomy were followed during rehabilitation by video fiberoptic laryngoscopy examination. Complications of aspiration (23/50), airway stenosis (13/50), and phonation dysfunction (16/24) were followed. Spontaneous resolution of aspiration may require a prolonged course. A majority of patients (37/50) had improvement and could be decannulated. Prognostic factors correlated to eventual decannulation included age, level on the Glasgow Coma Outcome Scale, and type of head injury. Those with poor neurologic improvement and glottic incompetence (13/50) are poor candidates for decannulation. Significant airway stenosis can involve both laryngeal and tracheal sites. Neurologic dysfunction may complicate the decannulation process after airway anatomy has been restored by surgery. Dysphonia resulting from intubation, peripheral laryngeal and nerve injury, or central laryngeal movement dysfunction are common. Preventive maintenance with ongoing evaluation can avoid airway crises such as aspiration pneumonia, hemoptysis, and innominate artery.     

Aberrant recurrent laryngeal nerve reinnervation as a cause of stridor and laryngospasm

Unilateral vocal fold paralysis rarely presents with symptoms of stridor, laryngospasm, and dyspnea. Abnormal reinnervation of abductor nerve branches into adductor fibers may be one cause. Four patients have been positively identified by laryngeal electromyography. Two patients presented after thyroid surgery for thyroid neoplasm. One presented after cervical disk surgery. One patient presented after herpes simplex infection with multiple cranial nerve involvement. All patients had new onset of dyspnea with exertion many months after the recurrent nerve injury. Fiberoptic laryngoscopy showed the affected vocal fold to be immobile. However, with hyperventilation and deep inspiration, there was paradoxical adductor motion of the paretic vocal fold. Laryngeal electromyography showed evidence of reduced but intact voluntary motor units in the thyroarytenoid muscle. These motor units fired on inspiration and not on phonation. This pattern was not seen on the normal side. These findings are consistent with paradoxical innervation and/or synkinesis. Each patient was managed by Botox injection into the adductor muscle. Periodic reinjections may be necessary to manage the condition.     

Laryngeal reinnervation for unilateral traumatic recurrent laryngeal nerve injuries]

OBJECTIVE: To investigate 5 procedures of laryngeal reinnervation for unilateral vocal cord paralysis induced by traumatic recurrent laryngeal nerve injury. METHODS: 35 cases were selected for our study, all patients had unilateral recurrent laryngeal nerve injury, including 8 for nerve decompression, 6 for end to end anastomosis of recurrent laryngeal nerve, 16 for main branch of ansa cervicalis anastomosis to recurrent laryngeal nerve, 3 for nerve muscular pedicle and 2 for nerve implantation. All cases have been subjected to preoperative and postoperative voice recording, acoustic analysis, videolaryngoscopy, strobscopy and electromyography. RESULTS: It is found the adductory and abductory motion of the vocal cord restored in 5 cases with less than 4 months course who received nerve decompression. Although functional motion of vocal cord was not seen in two patients who received nerve decompression with a course longer than 4 months and one less than 4 months, and in all cases who received ansa cervicalis anastomosis and end to end anastomosis of recurrent laryngeal nerve, these procedures resulted in medialization of vocal cord and the mass and tension of the reinnervated vocal cord may become much the same as the contralateral normal vocal cord, thus resuming symmetric vibration of the vocal cords and physiological phonation. Nerve muscular pedicle technique and nerve implantation enabled adductory muscles to be reinnervated, thus improving severe hoarseness, but they didn't restore normal voice. CONCLUSIONS: (1) Nerve decompression seems to be the best procedure in laryngeal reinnervation; (2) Main branch of ansa cervicalis technique raises satisfactory reinnervation of adductor muscles; (3) Selection of the laryngeal reinnervation protocols should depend on the course, severity and type of nerve injury.     

Electromyographic findings in recurrent laryngeal nerve reinnervation

Abductor, adductor, and combined reinnervation procedures have been explored with variable success rates. We describe the experience of a tertiary care center with adductor reinnervation procedures, including preoperative and postoperative videostroboscopy and electromyography (EMG) findings. A retrospective chart review was performed from 1997 to 2001 that included 9 patients. Preoperative and postoperative voice comparison was performed by 3 blinded speech pathologists. Clinical comparisons of videostroboscopy findings for vocal fold bulk, tone, position, presence of gap, and movement are elucidated. The preoperative and postoperative EMG findings are described. In all patients, preoperative EMG revealed a dense, complete denervation of the affected recurrent laryngeal nerve. No movement was noted on videostroboscopy with persistent glottic gap. Reinnervation involved a nerve-muscle pedicle or a direct neurorrhaphy of the ansa cervicalis to the recurrent laryngeal nerve. Voice improvement was noted between 60 days and 3 months after reinnervation. Four postoperative EMG studies were performed. An early postoperative EMG study at 5 months revealed activation of the lateral cricoarytenoid muscle and thyroarytenoid muscle with head-lift. Videostroboscopy showed excellent near-midline static positioning of the vocal fold. Late EMG studies, performed 12 to 16 months after reinnervation, revealed "learning" of these muscles, with new activation on "eee" phonation. We conclude that recurrent laryngeal nerve reinnervation procedures belong in the armamentarium of the laryngologist for the treatment of vocal fold paralysis. The EMG findings reported in this study suggest that ongoing reinnervation allows for activation with phonation in matured neuronal anastomoses. Overall, this procedure results in excellent patient acceptance and near-normal vocal quality.     

Studies of early laryngeal reinnervation

In 1973, Hengerer and Tucker reported a method for laryngeal reinnervation. The purpose of this study is to objectively verify the reinnervation mechanism in 20 dogs with nerve-muscle pedicle grafts. Three months after the experimental operation direct stimulation of the nerve to the neuromuscular pedicle produced an evoked action potential of the posterior cricoarytenoid muscle. This was recorded. Histologic examination of the posterior cricoarytenoid muscle and the nerve-muscle pedicle were performed. The electromyogram revealed in ten of fifteen dogs an excitable action potential. This can be considered as objective evidence for reinnervation from the neuromuscular pedicle.     

Laryngeal synkinesis: its significance to the laryngologist

Basic research and surgical cases have shown that the injured recurrent laryngeal nerve (RLN) may regenerate axons to the larynx that inappropriately innervate both vocal cord adductors and abductors. Innervation of vocal cord adductor muscles by those axons that depolarize during inspiration is particularly devastating to laryngeal function, since it produces medial vocal cord movement during inspiration. Many patients thought to have clinical bilateral vocal cord paralysis can be found to have synkinesis on at least one side. This will make the glottic airway smaller, particularly during inspiration, than would true paralysis of all the intrinsic laryngeal muscles. Patients with bilateral vocal cord paralysis should undergo laryngeal electromyography. If inspiratory innervation of the adductor muscles is present, simple reinnervation of the posterior cricoarytenoid muscle will fail. The adductor muscles also must be denervated by transection of the adductor division of the regenerated RLN.     

Restoration of the airway following bilateral recurrent laryngeal nerve paralysis

Bilateral recurrent laryngeal nerve paralysis has been treated by a number of ingenious techniques that include arytenoidectomies, vocal cord lateralizations, cordectomies, and, recently, reinnervation procedures and laser arytenoidectomies. An arytenoidectomy is recommended by a thyrotomy approach without lateralization of the vocal cord. The resulting airway is adequate for decannulation by expansion of the posterior glottic aperture, with preservation of the anterior glottis for phonation.     

Functional laryngeal abduction following reimplantation of the recurrent laryngeal nerves

Functional reinnervation was established in a patient following complete laryngo-tracheal separation with avulsion of both recurrent laryngeal nerves. Following reattachment of the larynx to the trachea, the severed stumps of the recurrent laryngeal nerves were implanted into the laryngeal abductors (the posterior crico-arytenoid muscles). One year later the patient had good abduction and adduction of her vocal cords. The abduction is thought to be a result of reinnervation by the recurrent laryngeal nerves, the adduction due to the action of crico-thyroid muscle whose innervation was undisturbed by the original injury.     

Quantitative assessment of laryngeal muscle morphology after recurrent laryngeal nerve injury: right vs. left differences

Objectives/Hypothesis: Reports of laryngeal response to denervation are inconsistent. Some document atrophy and fibrosis in denervated laryngeal muscles, whereas others indicate resistance to atrophy. Spontaneous reinnervation has also been documented. The goal of this study was to clarify the effects of nerve injury and reinnervation on thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles. Study Design: Laboratory experiment. Methods: TA and PCA muscles of cats were harvested 5 to 6 months after transecting right or left recurrent laryngeal nerve (RLN). Images of muscle cross‐sections were acquired and studied using an image analysis workstation. Cross‐sectional areas as well as total cross‐sectional area of randomly selected muscle fibers were recorded. Results: TA reinnervation was robust on both sides, but there was less reinnervation of the PCA muscle after left‐sided RLN lesion than after right‐sided injury. Conclusions: Differences in reinnervation after RLN injury could contribute to the higher clinical incidence of left‐ vs. right‐sided laryngeal paralysis.     

Regeneration of the recurrent laryngeal nerve in the guinea pig: reorganization of motoneurons after freezing injury

The purpose of this study was to clarify the morphologic changes resulting from reinnervation after a freezing injury. We chose the freezing injury as the most promising nerve regeneration model in order to examine the mechanism behind the production of misdirected reinnervation. The left recurrent laryngeal nerve of the adult guinea pig was injured by freezing (-80 degrees C) at the level of the 10th tracheal ring. At intervals ranging from 2 weeks to 6 months after the injury, horseradish peroxidase was injected into the left posterior cricoarytenoid muscle to ascertain the presence of retrograde-labeled perikarya in the medulla oblongata. Projections to the individual laryngeal muscles and to the entire recurrent laryngeal nerve served as normal controls. In addition, we observed by electron microscopy the degeneration and regeneration processes of the recurrent laryngeal nerve following injury. From 2 to 6 months after the freezing injury, the number of labeled neurons in the nucleus ambiguus increased gradually from 20 to 90. In addition, the area occupied by neurons which project to the posterior cricoarytenoid muscle was expanded, but was confined within the region of perikarya projecting to the normal recurrent laryngeal nerve. Most axons degenerated within 3 days and showed regenerative sprouting with growth cones by 7 days postinjury. Despite the fact that freezing injury preserved the basal lamina tunnel with minimal disturbance of the recurrent laryngeal nerve fiber structure, target-specific reinnervation was incomplete.     

Tracheo-tracheal puncture for voice rehabilitation after laryngotracheal separation

For patients with intractable aspiration, laryngotracheal separation (LTS) may be the only means of protecting the airway. The LTS prevents pulmonary compromise caused by aspiration; however, airway separation from the larynx also prevents laryngeal phonation. This case report suggests a supplemental procedure to the LTS, which maintains airway protection yet allows for laryngeal communication.     

膈神经替代喉返神经修复治疗双侧声带麻痹

目的 探讨膈神经喉返神经吻合和内收肌支环杓后肌植入术（膈神经手术）治疗双侧喉返神经损伤声带麻痹的有效性、可行性。方法 第二军医大学长海医院耳鼻咽喉科1999年8月－2001年7月治疗外伤性双侧喉返神经损伤声带麻痹6例。病程1周－18个月，一侧作膈神经手术，而另一侧作颈袢肌蒂环杓后肌植入术。手术前后电子喉镜、频闪喉镜观察声门大小、声珲运动、振动情况，噪音声学参数分析，喉肌电力产检查评价手术效果。结果 术后2－3周检查发现4例声门较术前增大2－3mm，但声带固定不动，2例无明显改善。术后6个月5例膈神经修复侧均恢复了较大幅度的吸气性声带外展功能，外展幅度可达3－5mm，而肌蒂植入侧仅轻微外展或固定不动，幅度均在1mm以内。此5例均顺利拔管，并能承受较大强度的体力活动，1例仍在随访中。术后4个月6例肌电图检查显示膈神经修复侧自发、诱发电位均明显大于肌蒂植入侧，自发电活动与肋间肌基本同步，而较肌蒂植入侧延迟100－200ms。声音估价显示3例声嘶术后较术前好转，2例无变化。术后半年肺功能均恢复正常。结论 膈神经喉返神经吻合内收肌支环杓后肌植入术安全可行，较颈袢肌蒂植入术更能有效地恢复声带吸气性外展运动，值得临床推广应用。     

Phonation and swallowing considerations in pediatric laryngotracheal reconstruction.

Experience with laryngotracheal reconstruction (LTR) has resulted in and continues to yield modifications and refinements in approach and technique with the goal to restore and maintain total laryngeal function. In addition to airway obstruction, the laryngeal functions of phonation and swallowing also may be affected by the underlying injury as well as by procedures designed to enlarge the airway. This paper discusses various problems encountered with phonation and swallowing in pediatric patients who underwent LTR and postoperative patients who were seen during the year July 1, 1990, through June 30, 1991. Phonation problems became apparent as long-term difficulties that persisted after tracheotomy decannulation. Swallowing was frequently a short-term perioperative problem while a stent was in place following LTR. The approaches and techniques that have been employed to treat, minimize, and prevent these problems are discussed.     

A quantitative study of the medial surface dynamics of an in vivo canine vocal fold during phonation

OBJECTIVES/HYPOTHESIS: The purpose of this study was to measure the medial surface dynamics of a canine vocal fold during phonation. In particular, displacements, velocities, accelerations, and relative phase velocities of vocal fold fleshpoints were reported across the entire medial surface. Although the medial surface dynamics have a profound influence on voice production, such data are rare because of the inaccessibility of the vocal folds. STUDY DESIGN: Medial surface dynamics were investigated during both normal and fry-like phonation as a function of innervation to the recurrent laryngeal nerve for conditions of constant glottal airflow. METHODS: An in vivo canine model was used. The larynx was dissected similar to methods described in previous excised hemilarynx experiments. Phonation was induced with artificial airflow and innervation to the recurrent laryngeal nerve. The recordings were obtained using a high-speed digital imaging system. Three dimensional coordinates were computed for fleshpoints along the entire medial surface. The trajectories of the fleshpoints were preprocessed using the method of Empirical Eigenfunctions. RESULTS: Although considerable variability existed within the data, in general, the medial-lateral displacements and vertical displacements of the vocal fold fleshpoints were large compared with anterior-posterior displacements. For both normal and fry-like phonation, the largest displacements and velocities were concentrated in the upper medial portion. During normal phonation, the mucosal wave propagated primarily in a vertical direction. Above a certain threshold of subglottal pressure (or stimulation to the recurrent laryngeal nerve), an abrupt transition from chest-like to fry-like phonation was observed. CONCLUSIONS: The study reports unique, quantitative data regarding the medial surface dynamics of an in vivo canine vocal fold during phonation, capturing both chest-like and fry-like vibration patterns. These data quantify a complex set of dynamics. The mathematical modeling of such complexity is still in its infancy and requires quantitative data of this nature for development, validation, and testing.     

Motor Innervation of the Guinea Pig Interarytenoid Muscle: Reinnervation Process Following Unilateral Denervation

The authors investigated the process of denervation and reinnervation of the interarytenoid (IA) muscle in the guinea pig using transmission electron microscopy and glycogen depletion technique after unilateral transection of the recurrent laryngeal nerve (RLN) and superior laryngeal nerve to clarify the innervation pattern of the unpaired IA muscle. Anastomosis between the bilateral arytenoid branches was confirmed in the belly of the IA muscle. Five weeks after transection, all of the IA muscle fibers appeared to have been reinnervated by the contralateral RLN. As the arytenoid branch of the RLN runs together with that of the contralateral RLN in a single intramuscular nerve funiculus, it is possible that collateral sprouting branches grow and extend into the adjacent denervated Schwann's sheaths. The authors conclude that the unpaired IA muscle, as a whole, receives specific motor nerve supply from the bilateral RLNs, although each muscle fiber is innervated unilaterally.     

甲状腺手术喉返神经损伤规律及治疗的探讨

目的探讨甲状腺手术喉返神经损伤的规律及中早期神经减压的疗效。方法甲状腺手术喉返神经损伤单侧声带麻痹87例，其中行喉返神经探查65例，非手术治疗22例。探查术中观察喉返神经损伤部位、类型、程度及神经肌肉形态；对缝扎、粘连伤行神经减压治疗14例。治疗前后以喉镜、嗓音声学参数、肌电图检查等评价治疗效果。结果探查发现喉返神经被缝线结扎、瘢痕粘连压迫、断离分别占43％(28／65)、9％(6／65)、48％(31／65)。损伤部位以近环甲关节处多见，占75％(49／65)；甲状腺中下部占25％(16／65)。病程半年以内喉内肌及损伤处远端神经干萎缩并不严重，病程越长萎缩变性越明显。神经切断伤上述改变较缝扎伤及压迫伤更为明显；但病程18个月喉内肌仍可见肌纤维组织结构。病程3个月内神经减压10例中9例声带恢复了不同程度的内收及外展功能；病程3个月以内1例、3—5个月4例神经减压术后声带未恢复运动，但均恢复了正常的肌张力、肌体积，声带振动及黏膜波对称，嗓音亦恢复正常。非手术治疗组声嘶有改善，但嗓音未恢复正常，声带亦未恢复运动。结论通过喉返神经探查初步揭示甲状腺手术喉返神经损伤的规律，中早期喉返神经减压术能恢复声带生理性运动功能。     

甲状腺手术喉返神经损伤规律及治疗的探讨

目的 探讨甲状腺手术喉返神经损伤的规律及中早期神经减压的疗效。方法 甲状腺手术喉返神经损伤单侧声带麻痹87例,其中行喉返神经探查65例,非手术治疗22例。探查术中观察喉返神经损伤部位、类型、程度及神经肌肉形态;对缝扎、粘连伤行神经减压治疗14例。治疗前后以喉镜、嗓音声学参数、肌电图检查等评价治疗效果。结果 探查发现喉返神经被缝线结扎、瘢痕粘连压迫、断离分别占43％(28/65)、9％(6/65)、48％(31/65)。损伤部位以近环甲关节处多见,占75％(49/65);甲状腺中下部占25％(16/65)。病程半年以内者喉内肌及损伤处远端神经干萎缩并不严重,病程越长萎缩变性越明显。神经切断伤上述改变较缝扎伤及压迫伤更为明显;但病程18个月喉内肌仍可见肌纤维组织结构。病程3个月内神经减压10例中9例声带恢复了不同程度的内收及外展功能;病程3个月以内1例、3-5个月4例神经减压术后声带未恢复运动,但均恢复了正常的肌张力、肌体积,声带振动及黏膜波对称,嗓音亦恢复正常。非手术治疗组声嘶有改善,但嗓音未恢复正常,声带亦未恢复运动。结论 通过喉返神经探查初步揭示甲状腺手术喉返神经损伤的规律,中早期喉返神经减压术能恢复声带生理性运动功能。