Neurorrhaphy of the recurrent laryngeal nerve

Reinnervation of the Canine Posterior Cricoarytenoid Muscle with Sympathetic Preganglionic Neurons

This experiment investigated the reinnervation of the canine posterior cricoarytenoid (PCA) muscle with preganglionic neurons of the sympathetic nervous system. Six dogs had their right recurrent laryngeal nerve (RLN) sectioned. Four of these dogs had the sympathetic cervical trunk (SCT) implanted into the right PCA muscle, and the two remaining dogs served as denervated controls. Four months later all dogs underwent videolaryngoscopy, electromyography, and electrical stimulation of the SCT. The PCA muscles were excised, sectioned, and stained for glycogen and ATPase. All four experimental PCA muscles demonstrated electrically evoked abduction and tonic electromyographic activity. In two of the specimens, staining (ATPase and PAS) revealed areas of reinnervation with fiber type grouping and glycogen depletion. These results are consistent with the successful reinnervation of the PCA muscle. Further refinement of this technique could be of benefit to patients with bilateral vocal cord paralysis.

Morphologic correlates for laryngeal reinnervation

OBJECTIVE

To describe morphologic correlates for laryngeal reinnervation.

STUDY DESIGN

Review of anatomic experiments dealing with laryngeal innervation performed over a 25-year period.

METHODS

Description of results from experimental studies on the cat and human laryngeal muscles and nerve supply.

RESULTS

Despite separation of abductor and adductor laryngeal motor neurons in the central nervous system, the mixture of abductor and adductor axons in the recurrent laryngeal nerve indicates that selective re-innervation of an individual laryngeal muscle must be accomplished at the neuromuscular junction (NMJ) of the muscle. The optimal time for a reinnervating neural source to re-occupy vacated NMJ is at the time of denervation. If the reinnervation procedure is attempted long (>1 mo) after denervation, extraneous end plates of other neural systems must be eliminated to provide vacant NMJ. The nerve muscle pedicle (NMP) concept is an effective model for reinnervation of a laryngeal muscle provided its activity pattern is similar to that of the denervated muscle and its insertion into vacated NMJ is timely.

CONCLUSION

NMP offers a logical method for selective laryngeal muscle reinnervation. Critical to the success of NMP are the physiological input to the NMP and timing of NMP implantation.

Anatomy of the human internal superior laryngeal nerve

The mucosa of the larynx contains one of the most dense concentrations of sensory receptors in the human body. This sensitivity is used for reflexes that protect the lungs, and even momentary loss of this function is followed rapidly by life-threatening pneumonia. The internal superior laryngeal nerve (ISLN) supplies the innervation to this area, and, to date, the distribution and branching pattern of this nerve is unknown. Five adult human larynges were processed by using Sihler's stain, a technique that clears soft tissue while counterstaining nerves. The whole-mount specimens were then dissected to demonstrate the branching of the ISLN from its main trunk down to the level of terminal axons. The human ISLN is divided into three divisions: The superior division supplies mainly the mucosa of the laryngeal surface of the epiglottis; the middle division supplies the mucosa of the true and false vocal folds and the aryepiglottic fold; and the inferior division supplies the mucosa of the arytenoid region, subglottis, anterior wall of the hypopharynx, and upper esophageal sphincter. Several dense sensory plexi that cross the midline were seen on the laryngeal surface of the epiglottis and arytenoid region. The human ISLN also appears to supply motor innervation to the interarytenoid (IA) muscle. A detailed map is presented of the distribution of the ISLN within the human larynx. The areas seen to receive the greatest innervation are the same areas that have been shown by physiological experiments to be the most sensate: the laryngeal surface of the epiglottis, the false and true vocal folds, and the arytenoid region. The observation that the human ISLN appears to supply motor innervation to the IA muscle is contrary to current concepts of the ISLN as a purely sensory nerve. These findings are relevant to understanding how the laryngeal protective reflexes work during activities like swallowing. The nerve maps can be used to guide surgical attempts to reinnervate the laryngeal mucosa when sensation is lost due to neurological disease.

Experimental study on neurorrhaphy of the recurrent laryngeal nerve in dogs

The effectiveness of anastomosis of a divided recurrent laryngeal nerve was evaluated in six adult mongrel dogs. Videolaryngoscopy and evoked compound muscle action potentials in the intrinsic laryngeal muscles were performed at six months and the posterior cricoarytenoid muscles and recurrent laryngeal nerves were processed for histomorphometric studies. Recovery of compound muscle action potentials in all re-innervated muscles and histomorphometric findings confirmed a good grade of axonal regeneration. The most significant histomorphometric changes observed were: a reactive hypertrophy of type I fibres in the posterior cricoarytenoid muscles of the re-innervated side, and a high nerve fibre density in the distal stump to the anastomosis. However, incomplete recovery of motion and fasciculated movements of the re-innervated vocal folds were observed. Reduction of effective motor units in the re-innervated muscles might be a factor that cause incomplete restoration of vocal fold movements.

Recurrent laryngeal nerve palsy after thyroid gland surgery

Risk factors for recurrent laryngeal nerve (RLN) lesions after thyroid gland surgery were evaluated retrospectively in 1026 patients. RLN palsy occurred in 5.9 per cent; the incidence of permanent palsy was 2.4 per cent as 59 per cent of paralyses were transient. For euthyroid nodular goitre, Graves' disease, chronic lymphocytic thyroiditis, recurrent goitre and thyroid carcinoma, permanent nerve damage occurred in 1.7, 4, 5, 3.8 and 8 per cent of patients respectively. In relation to the number of nerves at risk, the incidence of permanent RLN palsy was 1.1 per cent for subtotal lobectomy and 4.0 per cent for total lobectomy. The overall incidence of permanent RLN palsy was 1.8 per cent of nerves at risk. There was no statistically significant difference between the number of RLN paralyses occurring after nerve exposure and that occurring after non-exposure in subtotal lobectomy, but in total lobectomy the permanent palsy rate increased from 3.8 to 7 per cent when the nerve was not exposed or identified (P < 0.01). Underlying thyroid disease, the extent of resection and exposure of the nerve in total lobectomy are risk factors for both transient and permanent RLN palsy.

Electrical pacing for dynamic treatment of unilateral vocal cord paralysis. Experiment in long-denervated muscle

In order to explore the possibility of clinical application of laryngeal pacing as a treatment for unilateral vocal cord paralysis, we examined the reactivity of atrophic muscle to electrical stimulation in dogs whose recurrent laryngeal nerves were damaged by crushing, dissection followed by resuturing, or a 3-cm neurectomy. The threshold level to induce enough vocal cord adduction reached the maximum at 2 weeks after nerve injury, decreased with time, and never surpassed 7 V in each case. On the basis of results of these preliminary probings, laryngeal pacing was conducted on a dog 15 months after resection of the laryngeal nerve. Adduction of the paralyzed vocal cord for synchrony with the intact cord was achieved by 7 V of electrical stimulation of the thyroarytenoid muscle that was triggered by signals from the cricothyroid muscle.

Selective reinnervation of the abductor and adductor muscles of the canine larynx after recurrent nerve paralysis

Functional rehabilitation of the larynx after unilateral vocal cord paralysis was attempted in the dog by selective reinnervation of the laryngeal muscles. The intralaryngeal branches of the right recurrent nerve were dissected. The adductor branch was anastomosed with the ansa cervicalis; the abductor branch was anastomosed with the trunk of the phrenic nerve either within the larynx or through the recurrent nerve, the adductor branch of which was sectioned. Results could be analyzed in seven dogs: mobility of the vocal cord was checked, and electromyography, stimulation of the nerves, and histologic studies were performed. Functional reinnervation of both the adductor and abductor muscles was obtained in only one case, with good abduction. Adduction was recorded in five cases. False-positive results emphasize the necessity of collecting several types of data before concluding that functional reinnervation has been accomplished. The reliability of the procedure can and must be improved.

Reinnervation of skeletal muscle with a neuromuscular pedicle

In the past decade the otolaryngologist has become interested in the problem of muscle reinnervation as it relates to laryngeal and facial paralysis. Although reinnervation by neuromuscular pedicle transfer has shown promising results in the laboratory and clinic, some investigators have had difficulty in achieving reliable results with this procedure. To further assess the technique's validity, we investigated the neuromuscular pedicle. This study utilized a strap muscle neuromuscular pedicle transfer to a contralateral strap muscle in the rabbit. The results were analyzed by the use of a number of independent measures, including electrical stimulation of the nerve, muscle contractibility, electromyography, enzyme histochemistry, reduced-silver staining for normal fibers, and the retrograde transport of the enzyme marker horseradish peroxidase. The physiologic and anatomic results demonstrated that morphologic and functional reinnervation of the experimentally isolated muscle by the transferred neuromuscular pedicle occurred. The most convincing data were produced by gross electrical stimulation, twitch and tetanic contraction, and horseradish peroxidase labeling. Electromyographic activity and other histologic findings supported the above conclusions.

Functional reconstruction for unilateral recurrent laryngeal nerve paralysis caused by thyroid cancer

Surgery for unilateral recurrent laryngeal nerve paralysis, which is caused by thyroid cancer, appearing within the past six months, should be aimed at improvement of the asymmetrical vocal cord and preservation of the stiffness and the mass of the vocal fold. To accomplish these aims, reconstructive surgery of the neuromuscular systems is available and it should be performed at the same time as thyroidectomy. Our surgical procedures for unilateral recurrent laryngeal nerve paralysis caused by thyroid cancer are reported along with some experimental investigations in dogs. Experimentally, muscle atrophy was prevented by neurorrhaphy or by free nerve grafting of the recurrent laryngeal nerve, although movement of the vocals cord was not recovered due to misdirected reinnervation and reduction of the end plates. In our study of functional reconstruction for unilateral recurrent laryngeal nerve paralysis, end-to-end anastomosis or free nerve grafting between the recurrent laryngeal nerve after extirpating the abductor muscle branch of this nerve was the most effective and practical method for improvement of the adductor function. Clinically reconstructive surgery was performed on five females suffering from thyroid cancer with unilateral recurrent laryngeal nerve paralysis. The abductor branch was cut selectively in four cases, followed by free nerve grafting of the ansa cervicalis and pedicle nerve muscle graft of the thyrohyoid muscle implanted in one case. Vocal cord atrophies were not observed and phonations were good in all cases six months after of operation. However, obvious adduction of the operated vocal fold at phonation was obtained only in two cases and other two cases showed slight adduction.

Experiments in laryngeal reinnervation

Laryngeal reinnervation surgical procedures were performed in 26 dogs. Nineteen animals comprise the data reported in this thesis. Two different operative procedures were investigated, the ansa hypoglossi neuromuscular pedicle in 5 dogs, and the split phrenic nerve graft in 14 dogs. The studies were designed to evaluate whether either procedure resulted in inspiratory abduction of the vocal cord: and, if so, the mechanism by which abduction was produced. Five dogs in Experiment 1 demonstrated similar results from the ansa hypoglossi neuromuscular pedicle procedure. Apparent vocal cord abduction was seen during hyperpnea from airway obstruction, but was abolished by superior laryngeal nerve transection, or detachment of the sternothyroid muscle. None of the nerves in the neuromuscular pedicles was electrically excitable. Fourteen dogs in Experiment 2 underwent the split phrenic nerve graft operation. Vocal cord abduction, synchronized with inspiration, was noted in 5 animals. Two dogs had inspiratory abduction in quiet respiration. Electromyography, nerve action potentials, endoscopic motion pictures, and histologic study confirmed that posterior cricoarytenoid muscle reinnervation had occurred via the nerve graft from the phrenic nerve. Vocal cord abduction and electromyographic activity in the posterior cricoarytenoid muscle were abolished by transection of the nerve graft or the phrenic nerve. Conclusions of the study include the following: 1. The neuromuscular pedicle procedure does not result in reinnervation of the posterior cricoarytenoid muscle the pedicle's nerve and muscle block. 2. The phrenic procedure may result in reinnervation of the posterior cricoarytenoid via the nerve graft, and inspiratory abduction of the paralyzed vocal cord. Failure of the phrenic procedure to produce reinnervation appeared to be due to a. recurrent laryngeal nerve regeneration, or b. avulsion of the nerve graft due to swallowing and other laryngeal movements.

Selective section of the recurrent laryngeal nerve for the treatment of spastic dysphonia: an experimental study and preliminary clinical report

The experimental and clinical results of the surgical treatment of patients with spastic dysphonia by selective section of the adductor branch of the recurrent laryngeal nerve are described. Experimental selective nerve section in dogs appears to retain cordal abduction during inspiration while producing a partial adductor paralysis. Selective section of the recurrent laryngeal nerve has been performed in four patients with 18- to 24-month follow-up. Speech results have been good with maintenance of partial vocal cord motion. No patient has experienced a return of spasticity. We theorize that selective nerve section may decrease the likelihood of the long-term failure that has been seen with complete nerve section by preventing medial fixation of the paralyzed vocal cord.