The recurrent laryngeal cardiac nerve in fetuses / El nervio laríngeo recurrente cardiaco en fetos

The recurrent laryngeal nerve has been reported to supply cardiac branches to the cardiac plexus. A review of anatomical literature on the existing term used to describe these branches revealed that varying interpretations and descriptions exist among various authors. Therefore, this study aimed to investigate the origin and incidence of branches from the recurrent laryngeal nerves to the cardiac plexus and their connections with sympathetic cardiac nerves. The sample comprised 40 cadaveric fetuses (n=80) (gestational ages: 16-30 weeks). The recurrent laryngeal cardiac nerve was described as the cardiac branch that originated directly from the recurrent laryngeal nerve and reached the superficial or deep parts of the cardiac plexus. This study found the recurrent laryngeal cardiac nerve in 76% of the cases contributing direct and indirect branches in 75% and 25% of the cases, respectively. This study recorded only two (2%) of these branches contributing to the superficial cardiac plexus while the rest (74%) of these branches contributed to the deep cardiac plexuses. The remaining 24% had no contributions from the recurrent laryngeal nerve to either the superficial or deep part of the cardiac plexus. The most common point of origin for the recurrent laryngeal cardiac nerve was at the lower distal part in 59% of the specimens. In the remaining 41% of branches, this nerve originated from the point of curvature, upper proximal part and both the point of curvature and lower distal part in 26%, 10% and 5% of the specimens.

El nervio laríngeo recurrente suministra las ramas cardiacas para el plexo cardíaco. Una revisión de la literatura anatómica nos muestra que existen diferentes interpretaciones y descripciones de estas ramas por parte de los distintos autores consultados. En consecuencia este estudio tuvo como objetivo investigar el origen, además de la incidencia de las ramas de los nervios laríngeos recurrentes al plexo cardíaco y sus conexiones con los nervios cardiacos simpáticos. La muestra incluyó 40 fetos (n=80) (edades gestacionales: 16-30 semanas). El nervio laríngeo recurrente cardiaco fue descrito como la rama cardíaca que se originó directamente del nervio laríngeo recurrente, que llega a las partes superficiales o profundas del plexo cardíaco. En este estudio observamos que el nervio laríngeo recurrente cardiaco en el 76% de los casos contribuye a las ramas directas e indirectas, en el 75% y el 25% de los casos, respectivamente. Se observó en este estudio que solamente dos (2%) de estas ramas contribuían en la formación del plexo cardíaco superficial, mientras que el resto (74%) de estas ramas contribuía a los plexos cardíacos profundos. El 24% restante no tenía contribuciones del nervio laríngeo recurrente ya sea para la parte superficial o profunda del plexo cardíaco. El punto de origen más común del nervio laríngeo recurrente cardiaco se observó en la parte distal inferior en un 59% de las muestras. En el 41% restante de las ramas este nervio se originó desde el punto de curvatura, la parte proximal superior y tanto en el punto de curvatura inferior como la parte distal en 26%, 10% y 5% de los especímenes.

Morphologic evaluation of the fetal recurrent laryngeal nerve and motor units in the thyroarytenoid muscle.

This study is a morphologic description of the recurrent laryngeal nerve (RLN) and of the number and size of motor units (MUs) in the thyroarytenoid (TA) muscle bilaterally of a human fetus aged 25 weeks. A quantitative analysis of RLN and MUs is presented to investigate similarities with equivalent structures in adults. In the fetus used in our study, the morphologic organization of the RLN was similar to that commonly described in the adult RLN. Moreover, as is observed in adult TA, the TA of the analyzed fetus, particularly the right TA, showed MUs typical of muscles with great motor accuracy. These results may be used to increase our knowledge of the features of the voice in adults and newborns.

Embryologic innervation of the rat laryngeal musculature--a model for investigation of recurrent laryngeal nerve reinnervation.

OBJECTIVES/HYPOTHESIS: Optimal management of vocal fold paralysis would entail recurrent laryngeal nerve (RLN) reinnervation resulting in normal vocal fold motion. Unfortunately, RLN reinnervation currently results in a nonfunctional vocal fold due to synkinetic reinnervation. Therapeutic interventions that guide regenerating axons back to the appropriate muscle would prevent synkinesis and restore vocal fold and glottal function. The initial step toward developing these therapies is the elucidation of the embryologic innervation of the larynx. This study aimed to identify the age of occurrence, timing, and pattern of embryologic innervation of the rat larynx, hypothesizing that differences in these parameters exist between distinct laryngeal muscles. STUDY DESIGN: Descriptive anatomic study. METHODS: The larynx of rats aged embryologic day (E) 15, 16, 17, 19, and 21 were harvested and then sectioned. Two rats were used for each age. Sections were colabeled with neuronal class III ß-tubulin polyclonal antibody to identify the presence of axons and alexa 488 conjugate α-bungarotoxin to identify the presence of motor endplates. The age at which axons and motor endplates were first present was noted. The position and pattern of the axons and motor endplates was recorded in relation to each other as well as the musculoskeletal anatomy of the larynx. The time at which axons appeared to innervate the medial thyroarytenoid (MTA) muscle, lateral thyroarytenoid (LTA) muscle, and the posterior cricoarytenoid (PCA) muscle was documented. RESULTS: Findings in the rat suggest the RLN reaches the larynx and begins branching by E15. Axons branch dorsally first and reach the PCA muscle before the other muscles. Branching toward the MTA muscle occurs only after axons have reached the LTA muscle. By E19, RLN axons have been guided to and selected their respective muscles with formation of neuromuscular junctions (NMJs) in the PCA, LTA and MTA muscles, though the formation of NMJs in the MTA muscle was comparatively delayed. CONCLUSIONS: This study describes the embryologic innervation of the rat larynx and suggests that there are distinct differences in the age of occurrence, timing, and pattern of innervation of the PCA, LTA, and MTA muscles of the rat. These findings lay the foundation for studies investigating the role of guidance cues in RLN axon guidance and the utility of these cues in the treatment of RLN injury via the stimulation of functional, nonsynkinetic reinnervation.

Surgical anatomy of the thyroid and parathyroid glands.

This article describes the anatomy and embryology of the thyroid and parathyroid glands and the recurrent laryngeal nerve, discussing how the anatomy affects function and dysfunction of the glands.

[The right inferior laryngeal nerve with a non-recurrent course]. / Il nervo laringeo inferiore destro a decorso non ricorrente.

Two cases of a right non-recurrent laryngeal nerve were encountered during the performance of 992 thyroid operations. In its abnormal non-recurrent course the nerve passes transversely from under the carotid sheat hand takes a position which is at right-angles to the normal recurrent laryngeal nerve.

The inferior non recurrent laryngeal nerve: a major surgical risk during thyroidectomy.

It is now widely established that systematic intraoperative location and diligent dissection of the recurrent inferior laryngeal nerve during thyroidectomy are the keystones to assure its anatomic and functional preservation. The possibility of abnormal routes, like a non-recurrent cervical course of the inferior laryngeal nerve is an additional major argument for its systematic identification to avoid surgical damage. In 2517 cervicotomies performed between 1992 and 1997 for at least right thyroid lobe excision or parathyroid glands exploration, 20 cases of non recurrent laryngeal nerve were identified (0.79%). The embryological nature of such a nervous anatomical variation results originally from a vascular disorder, named arteria lusoria in which the fourth right aortic arch is abnormally absorbed, being therefore unable to drag the right recurrent laryngeal nerve down when the heart descends and the neck elongates during embryonic development. The surgeon must be aware of the possibility of a non recurrent laryngeal nerve, which arises directly from the cervical vagus and therefore represents a severe potential pitfall during thyroidectomy. Given the absence of reliable clinical symptoms and signs or investigations indicating preoperatively the possibility of a non recurrent nerve, guidelines are given to prevent intraoperatively this major surgical risk.

Non-recurrent laryngeal nerve: identification during thyroid surgery.

The non-recurrent course of the inferior laryngeal nerve is a rare anomaly. The incidence varies from 0.3 to 4% on the right side. It is extremely rare on the left side. The awareness of such an anomaly is essential as the risk of damage to the nerve is higher during thyroid surgery. Two cases of non-recurrent laryngeal nerve are reported, and the embryology and method of identification are discussed.

[Surgical discovery of parathyroid glands and the recurrent laryngeal nerve. Application of well known embryological concepts in the operating room]. / La découverte chirurgicale des glandes parathyroïdes et du nerf laryngé récurrent. Application en salle d'operation des notions embryologiques connues.

Surgery for thyroid or parathyroid glands has to be logical. It is based upon a precise knowledge of the development of the 3rd and 4th pharyngeal pouches and aortic arches. Pharyngeal pouches are endodermal derivatives of the lateral walls of the early foregut. Parathyroid glands have an ectodermal origin in concert with inductive forces of cells derived from the neural crest (which also creates parafollicular cells secreting calcitonin). From the third pouch thymus and parathyroid III move down together because of the cervical flexure and heart's "descent" (stages 14 to 20 mm). The fourth pouch gives rise to the so called "caudal pharyngeal complex" constituted by parathyroid IV dorsally, a "lateral thyroid" ventrally and an ultimo-branchial body derived from the fifth pouch. The thyroid gland first appears at the 4th week as a thickening of the endoderm of the floor of the pharynx which evaginates as a diverticulum in front of the trachea below. This medial component of the thyroid joins both lateral thyroids derived from the caudal pharyngeal complexes to form a bi-lobed structure with an isthmus. The lateral edge of the adult thyroid lobe has a thickening which is called Zuckerkandl's tuberculum because of the fusion of the ultimobranchial body into the principal médial thyroid process. This tuberculum lies in front of the caudal thyroid artery born from the 4th aortic arch. The recurrent laryngeal nerve courses round the 4th aortic arch: therefore parathyroids IV have to be above and behind the nerve and parathyroids III below and in front of the nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

[The non-recurrent inferior laryngeal nerve. An important rarity in thyroid gland surgery]. / Der Nervus laryngeus inferior non-recurrens. Eine wichtige Rarität in der Schilddrüsenchirurgie.

The occurrence of non-recurrent inferior laryngeal nerve is based on a rare embryologic vascular malformation of the aortic arches. Based on three recent cases, we discuss embryology, clinical presentation and operative technique.

Extralaryngeal division of the recurrent laryngeal nerve. Report on 400 patients and the 721 nerves measured.

Seven hundred twenty-one recurrent laryngeal nerves were visualized in 400 patients having thyroid or parathyroid surgery. Four hundred twenty-one nerves (58 percent) bifurcated or trifurcated more than 0.5 cm from the cricoid cartilage. Ninety-seven patients had bilateral bifurcations, and 10 patients had trifurcations. Six patients had direct laryngeal nerves, all on the right side. One patient had a direct laryngeal and a recurrent laryngeal nerve simultaneously, and one patient had a bifurcated recurrent laryngeal nerve with an accessory vagus nerve joining it 13.5 cm from the cricoid cartilage. Damage to any of the filaments of the recurrent laryngeal nerve to the cricothyroid musculature or to or from a variant direct laryngeal nerve or variant vagus nerve connection can cause vocal cord paralysis. Damage to any branches of the recurrent laryngeal nerve to the esophagus can cause dysphagia. Therefore, if possible, all branches of the recurrent laryngeal nerve, no matter how small, should be preserved.

Anatomy of the recurrent laryngeal nerve: a redescription.

The recurrent laryngeal nerves on each side of the neck consist of numerous branches. The demonstration of the diverse relationships of the recurrent laryngeal nerve in the thyroid area explains the variation in vocal cord and cricopharyngeal muscle paralysis produced by surgical or other trauma to this area. The anastomosis of the middle cervical ganglion with the recurrent laryngeal nerve adds a new dimension to the already confused theories on vocal cord and laryngeal function. Both the motor and sensory supply of the larynx inferior to the cords, lower pharynx, cervical oesophagus and cervical trachea are supplied by the recurrent laryngeal nerve branches and their sympathetic anastomoses. The blood vessel-nerve relationship in these neck dissection specimens is quite different from that documented in the standard literature in that there are numerous blood vessels from the inferior thyroid artery that interdigitate with the branches of the recurrent laryngeal nerve.

Role of the vagus nerve and its recurrent laryngeal branch in the development of the human ductus arteriosus.

The reason that the normal ductus arteriosus has a muscular media, contrasting with the elastic lamellar structure of the adjacent great arteries, is unknown. We examined the hypothesis that the anatomic relationship of the ductus arteriosus to the vagus and recurrent laryngeal nerves during early development might be of importance in influencing ductal morphology. Normal human embryos from the Carnegie Embryological Collection and embryos and fetuses from the Hopkins Pathology Collection were studied microscopically, by reconstructions made from serial histologic sections, or by gross dissection. At Carnegie stage 16 the recurrent laryngeal nerves pass medially from the vagus nerve to the laryngeal area and are caudal to the bilaterally symmetric sixth aortic arches. By stage 18 the right sixth aortic arch has disappeared and the left sixth aortic arch is in a more caudal position relative to the larynx. The left vagus nerve and its recurrent laryngeal branch form a sling supporting the distal (or ductus arteriosus component) of the left sixth aortic arch. In subsequent development there is greater relative separation of the larynx and ductus arteriosus. The media of the ductus arteriosus beneath the supporting nerves is thinner and has less elastic fiber formation than the elastic lamellar media of the adjacent aortic arches. The study shows that the vagus and recurrent laryngeal nerves are in a position to provide mechanical support to the ductus arteriosus during its development and that the morphology of the media of the supported ductus arteriosus differs from that of the adjacent unsupported aortic arches. It is suggested that this local mechanical support may be the reason that the normal ductus arteriosus differentiates as a muscular artery and is therefore able to obliterate its lumen in postnatal life. Without such support the ductal media could develop the abundant elastic fibers characteristic of the normal unsupported aorta and pulmonary trunk and become an abnormal, persistently patent ductus arteriosus.

Non-recurrent laryngeal nerve.

Two cases of a right non-recurrent nerve were encountered in 203 thyroidectomies. In its abnormal, non-recurrent course the nerve passes transversely from under the carotid sheath and takes a position which is at right-angles to the normal recurrent laryngeal nerve.

Embryological considerations of thyroid surgery: developmental anatomy of the thyroid, parathyroids and the recurrent laryngeal nerve.

The surgeon planning a thyroidectomy must be prepared to find variations in three important structures in the neck. He must be prepared to find ectopic thyroid nodules above, below or lateral to the normally located thyroid gland. Any unattached nodule should be considered malignant until proved otherwise. He must identify and preserve parathyroid glands that may not lie in the typical location. He must be prepared to encounter recurrent laryngeal nerves that do not recur. The surgeon who remembers the embryology of the structures in the neck may occasionally be astonished, but never surprised.