Electron microscopic study of muscle spindle in human interarytenoid muscle

Using transmission electron microscopy, the fine structure of the muscle spindle in the interarytenoid muscle was studied. The specimen was made from a fresh adult male larynx which had been surgically removed. The muscle spindle showed the following characteristic features: (1) the capsule was thin, with only a small number of layers of capsular sheet cells; (2) the periaxial space was narrow and there were abundant collagenous fibrils; (3) the sensory endings consisted of irregularly coiled terminal axons with varicose swellings, and some endings penetrated the sarcoplasm; (4) one nuclear chain fiber terminated on the capsule, while the other branched into two bundles; and (5) special sarcoplasmic inclusions, possibly related to the sensory endings, were also observed. These findings suggest that the muscle spindle in the interarytenoid muscle is not only a very sensitive stretch receptor, but also a pressure receptor.     

Motor end-plate distribution in the human interarytenoid muscle

Histochemical and computer graphic techniques were used to determine the distribution of neuromuscular junctions in the human interarytenoid (IA) muscle. The motor end-plates of four IA specimens obtained from normal postmortem larynges were visualized using an acetylcholinesterase stain. The three-dimensional distribution of motor end-plates was later reconstructed using computer graphics. The motor end-plates in the IA were found to be distributed in an inverted "Y" configuration. A broad band of end-plates was found at the midpoint of the muscle fibers in the superior and middle aspect of the muscle. This band divided obliquely in a lateral direction toward the inferior border of the muscle. This pattern of motor end-plate distribution is possibly consistent with the bilateral innervation of the IA by the recurrent laryngeal nerves.     

Anatomy and fiber type composition of human interarytenoid muscle

Intrinsic laryngeal muscle investigations, especially those of the interarytenoid (IA) muscle, have been primarily teleologically based. We determined IA muscle anatomy and histochemical and immunohistochemical classification of extrafusal and intrafusal (muscle spindle) fibers in 5 patients. Extrafusal fibers were oxidative type I and glycolytic types IIA and IIX. Intrafusal fibers of muscle spindles were identified by the presence of tonic and neonatal myosin. The results demonstrate that the IA muscle has a phenotype similar to that of limb skeletal muscle. Myosin coexpression, the absence of intrafusal fibers, and fiber type grouping were unusual features found previously in the thyroarytenoid and posterior cricoarytenoid muscles, but they were not present in the IA muscle. These findings lead to the conclusion that the IA muscle has functional significance beyond its assumed importance in maintaining vocal fold position during phonation. The presence of spindles demonstrates differences in motor control as compared to the thyroarytenoid and posterior cricoarytenoid muscles. Further, extrafusal fiber characteristics implicate IA muscle involvement in muscle tension dysphonia and adductor spasmodic dysphonia. Given the unique physiologic characteristics of the human IA muscle, further research into the role of the IA muscle in voice disorders is warranted.     

Motor innervation of the human cricopharyngeus muscle

Innervation of the human cricopharyngeus muscle remains historically controversial and unclear, encouraging numerous treatments inconsistently designed to pharmacologically or mechanically alter the contractile state of this muscle. Neuroanatomic controversy results from and is perpetuated by 1) use of nonhuman models, 2) observational misinterpretation of small-diameter, overlapping nerve fibers, and, most importantly, 3) lack of real-time verification of neural projections. We sought to overcome these difficulties by performing microdissections in 27 patients undergoing laryngectomy and using real-time electromyographic verification. We demonstrated 1) dual ipsilateral innervation by the pharyngeal plexus and recurrent laryngeal nerve, 2) segmental projection of the recurrent laryngeal nerve to anterior motor units, 3) pharyngeal plexus projection to posterior motor units, 4) absence of a sympathetic or external superior laryngeal nerve contribution, and 5) absence of contralateral innervation. Such dual ipsilateral innervation, segmentally projected, has not been previously described in any other form of neuromuscular organization. Neuroanatomic accuracy should improve diagnostic and therapeutic strategies for future management of pharyngeal dysphagia.     

The superior laryngeal nerve and the interarytenoid muscle in humans: an anatomical study

The course and distribution of the rami perforantes of the superior laryngeal nerve was studied in 12 human larynges. Dissections utilized a Zeiss operating microscope. All branches were found to perforate the muscle; none terminated in the muscle. This eliminates anatomically any possibility of motor supply to the mterarytenoid muscle from the superior laryngeal nerve. The rami perforantes also contribute to mucosal innervation on the posterior surface of the larynx. Histologic studies of whole fetal larynges corroborated the findings from the dissections. No evidence of innervation across the midline was found. No extra-laryngeal division of the recurrent laryngeal nerve into abductor and adductor branches was found. A ganglion around the superior laryngeal nerve was described.     

Treatment of the interarytenoid muscle with botulinum toxin for laryngeal dystonia

The treatment of laryngeal dystonia with botulinum toxin has provided various degrees of relief to the majority of patients with adductor dysphonia; however, a significant number of patients have limited or no improvement with this type of therapy. It remains unclear why some patients respond to the routine administration of toxin to the thyroarytenoid muscles whereas others do not. Injections into the lateral cricoarytenoid muscles have provided an improved voice in some patients who were unresponsive to injections into the thyroarytenoid muscles. Fine-wire electromyography can demonstrate the particular dystonic activity of these muscles to help determine which muscle is predominantly involved. It can also demonstrate dramatic dystonic activity in the interarytenoid (IA) muscle in many patients. We present the results of 23 patients treated with injections to the IA muscle after demonstration of dystonic IA activity. Ten have benefited from IA therapy. Five of these 10 patients did not have a good result from botulinum toxin until IA injections were added to the treatment plan. In 8 patients, IA therapy provided no improvement, and 5 patients were lost to adequate follow-up. According to fine-wire electromyography and clinical response, the IA muscle is an active dystonic muscle in some patients with laryngeal dystonia and should be treated with botulinum toxin in selected patients.     

The innervation of the human posterior cricoarytenoid muscle: Evidence for at least two neuromuscular compartments

Recent work has demonstrated that the dog posterior cricoarytenoid (PCA) muscle is composed of three neuromuscular compartments: a vertical, an oblique, and a horizontal. In this study, the human PCA muscle was examined for evidence of neural compartments. Fifteen human PCA muscles were processed by Sihler's stain, which renders the muscle translucent while counterstaining the nerve supply. The results clearly show that in all specimens the nerve supply of the human PCA muscle is separated into at least two main branches: one supplies the horizontal compartment and a second further subdivides to innervate both the vertical and oblique compartments. In 10 of the specimens, these nerve branches arose as separate branches from the recurrent laryngeal nerve. In all specimens, the nerve branch to the horizontal compartment was either combined or connected with the nerve branch to the interarytenoid muscle. The results suggest that the different compartments of the PCA muscle have distinct functions. In addition, the strong connections with the interarytenoid nerve complicate reinnervation procedures to reanimate a paralyzed or transplanted larynx.     

Rare intramuscular haemangioma of the sternocleidomastoid muscle

Intramuscular tumours of the head and neck often represent a differential diagnostic challenge. We report the rare case of an intramuscular haemangioma arising from the sternocleidomastoid muscle in the 6th decade. Pre-operative diagnosis was difficult, as these tumours are extremely uncommon in the head and neck region, with only very few cases reported in the literature. Due to the marked tendency of intramuscular hemangiomas to recur, accurate preoperative diagnosis forms the basis of adequate surgical therapy with sufficient safety margins.     

Well-circumscribed intramuscular lipoma of the sternocleidomastoid muscle

Intramuscular lipomas are unusual benign mesenchymal tumours, which infiltrate the skeletal muscle, and are exceedingly rare in the head and neck region. They commonly infiltrate the skeletal muscle fibres from which they arise and are rarely well circumscribed. We present the only documented case of well-circumscribed intramuscular lipoma arising from the sternocleidomastoid muscle. Although the recurrence is commoner in the infiltrative variety the surgeon should be aware that differentiation between infiltrative and well circumscribed is based on histological diagnosis, and hence wide excision in all cases of intramuscular lipomas is essential.     

The intramuscular nerve supply of the posterior cricoarytenoid muscle of the dog.

The paired posterior cricoarytenoid (PCA) muscle has three separate muscle bellies that differ in muscle fiber type (percentage of fast vs. slow twitch) and electromyelographic activity, and, in addition, produce different movements of the arytenoids when stimulated. An investigation of the innervation of the muscle was undertaken to demonstrate the existence of separate functional units. The intramuscular nerve supply of the PCA from five sacrificed dogs were microdissected. The intramuscular nerves of three additional dogs were removed and stained for acetylcholinesterase, which differentiates axons bound for fast- and slow-twitch muscle, and sensory end organs. Three separate fascicles are described entering the PCA muscle from a single branch of the recurrent laryngeal nerve. The three fascicles differ in axon type composition and in sensory, autonomic, and motor percentages, with the ratio of fast twitch to slow twitch varying from 0.78 to 1.5 to 1.7 (P less than .05). This variation supports separate functional capabilities for the three muscle bellies of the PCA.     

Motor innervation of the canine arytenoid muscle]

Dual motor innervation by the bilateral recurrent laryngeal nerves (RLNs) has been demonstrated in the human arytenoid muscle (AR). Whether AR of the dog receives dual motor innervation remains to be cleared yet, although the canine larynx is frequently used in experimental studies. To answer this question, the author observed the muscular structure in detail and anastomotic nerve branch between the bilateral RLNs, and then carried out glycogen depletion experiments on AR of dog compared with typical unpaired ARs of monkey and of guinea pig. 1) Muscular structure AR of the dog consisted of three parts of muscle bundles: the transverse arytenoid muscle (TVA), ventricular muscle (VT) and anonymous small bundle provisionally named the smaller interarytenoid muscle (IAm). While TVA and VT were paired type, IAm was unpaired type and lay horizontally on the dorsal aspect of the sesamoid cartilage around the midline. So the canine AR displayed a trigastric muscle as a whole. 2) Anastomotic nerve branch By the vital staining with methylene blue, the arytenoid branch of canine RLN ramified in three directions: anteriorly to the bellies of TVA and VT, medially to the anastomotic branch and superomedially to IAm. By the silver impregnation method of Barker and Ip, the bilateral IAm ramuli were found to form collateral anastomoses and terminate disorderly on the individual fibers. 3) Glycogen depletion experiments When an electrical stimulation was applied to the unilateral RLN in the monkey and the guinea pig, about one half of AR fibers were unstained with PAS staining and, in turn, these unstained fibers were known to be innervated by the ipsilateral RLN. While these unpaired ARs receive dual motor innervation as a whole muscle, every individual fiber is innervated by the unilateral RLN. In the canine VT and TVA, almost 90% of fibers were depleted of glycogen on the belly of the stimulated side, while the reverse was on the nonstimulated side. This finding suggests that most fibers of canine VT and TVA are ipsilaterally and the remaining fibers are contralaterally innervated. About one half of fibers of IAm were unstained and the others were stained. This pattern was similar to that observed in the monkey and the guinea pig. Therefore, IAm receives dual motor innervation from both RLNs as a whole muscle.     

Evidence for recurrent laryngeal nerve contribution in motor innervation of the human cricopharyngeal muscle.

OBJECTIVE: To study the functional motor nerve supply of the upper esophageal sphincter in humans. STUDY DESIGN: Intraoperative electromyographic study. METHODS: The contribution of the recurrent laryngeal nerve and the pharyngeal plexus in the motor nerve innervation of the cricopharyngeal muscle and the inferior pharyngeal constrictor muscle was examined intraoperatively. RESULTS: Electromyography showed that there is a considerable overlap in the innervation of the cricopharyngeal muscle and the inferior pharyngeal constrictor muscle. The recurrent laryngeal nerve functionally contributes to the motor innervation of the cricopharyngeal muscle in all patients and contributes to the motor innervation of the inferior pharyngeal constrictor muscle in most patients. The pharyngeal plexus functionally contributes to the motor innervation of the inferior pharyngeal constrictor muscle but does not always contribute to the motor innervation of the cricopharyngeal muscle. CONCLUSIONS: This is the first report which provides evidence that the recurrent laryngeal nerve functionally contributes to the motor innervation of the cricopharyngeal and inferior pharyngeal constrictor muscle. Furthermore, this study shows that intraoperative electromyography in humans is a feasible method to analyze the physiology of the motor innervation of the upper esophageal sphincter.     

The autonomic innervation of the human vocal cord: neuropeptides

Three methods have been used to study the sympathetic and parasympathetic innervation of the vocal cord: paraformaldehyde-induced fluorescence, electron microscopy, and the peroxidase-antiperoxidase technique. Each method has been successful in determining adrenergic fibers, autonomic endings, and the neuropeptides VIP and NPY, respectively. The close relationship between these neuropeptides and the autonomic endings (adrenergic and cholinergic), and the presence of the neuropeptides in the chorion of the vocal cord, around glands and vessels, gives new evidence that autonomic innervation plays a role in the functioning of this part of the larynx.     

The spiral ganglion and the innervation of the human organ of Corti

Five human cochleas were evaluated using the block surface method. The numbers of hair cells, nerve fibres in the osseous spiral lamina, and spiral ganglion cells were determined and correlated. The ultrastructural organization corresponds essentially to that of the mammalian ear, with the exception of multiple synaptic contacts of afferent nerve fibres with inner hair cells and surprisingly large numbers of outer spiral fibres.     

An unusual neck lump: intramuscular haemangioma of the sternocleidomastoid muscle

Neck lumps can often present a diagnostic dilemma, with a wide pre-operative differential diagnosis. We present an unusual case of an intramuscular haemangioma arising in the sternocleidomastoid muscle. Pre operative diagnosis is often difficult, as these lesions are extremely rare in the head and neck region and only few sporadic cases have been reported in the literature. We report the presentation diagnosis and management of intramuscular haemangiomas of the sternocleidomastoid muscle.     

Oncocytic variant of a ductal retention cyst in the interarytenoid region

Laryngeal cysts are a mixed group of benign lesions that have been classified as per their site of origin and histopathology. We report a case of an interarytenoid cyst in a 56 year old male with hyperparathyroidism. The cyst was resected under an operating microscope using KTP532 laser. It was reported on histopathology as an oncocytic variant of a ductal retention cyst.