Function

The recurrent laryngeal nerves control all intrinsic muscles of the larynx except for the cricothyroid muscle. These muscles act to open, close, and adjust the tension of the vocal cords, and include the posterior cricoarytenoid muscles, the only muscle to open the vocal cords. The nerves supply muscles on the same side of the body, with the exception of the interarytenoid muscle, which is innervated from both sides. The nerves also carry sensory information from the mucous membranes of the larynx below the lower surface of the vocal fold, as well as sensory, secretory and motor fibres to the cervical segments of the esophagus and the trachea.

Clinical significance

Injury

Recurrent laryngeal nerve visible during resection of a goitre.

The recurrent laryngeal nerves may be injured as a result of trauma, during surgery, as a result of tumour spread, or due to other means. Injury to the recurrent laryngeal nerves can result in a weakened voice (hoarseness) or loss of voice (aphonia) and cause problems in the respiratory tract. Injury to the nerve may paralyze the posterior cricoarytenoid muscle on the same side. This is the sole muscle responsible for opening the vocal cords, and paralysis may cause difficulty breathing (dyspnea) during physical activity. Injury to both the right and left nerve may result in more serious damage, such as the inability to speak. Additional problems may emerge during healing, as nerve fibres that re-anastamose may result in vocal cord motion impairment, uncoordinated movements of the vocal cord.

Surgery

The nerve receives close attention from surgeons because the nerve is at risk for injury during neck surgery, especially thyroid and parathyroid surgery; as well as esophagectomy. Nerve damage can be assessed by laryngoscopy, during which a stroboscopic light confirms the absence of movement in the affected side of the vocal cords. The right recurrent laryngeal nerve is more susceptible to damage during thyroid surgery because it is close to the bifurcation of the right inferior thyroid artery, variably passing in front of, behind, or between the branches. The nerve is permanently damaged in 0.3–3% of thyroid surgeries, and transient paralysis occurs in 3–8% of surgeries; accordingly, recurrent laryngeal nerve damage is one of the leading causes of medicolegal issues for surgeons.

Tumors

The RLN may be compressed by tumors. Studies have shown that 2–18% of lung cancer patients develop hoarseness because of recurrent laryngeal nerve compression, usually left-sided. This is associated with worse outcomes, and when found as a presenting symptom, often indicates inoperable tumors. The nerve may be severed intentionally during lung cancer surgery in order to fully remove a tumor. The RLN may also be damaged by tumors in the neck, especially with malignant lymph nodes with extra-capsular extension of tumor beyond the capsule of the nodes, which may invade the area that carries the ascending nerve on the right or left.

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Regards
Lisa M
Editorial Team
Journal of Clinical & Experimental Neuroimmunology