What is the function and clinical significance of the recurrent laryngeal nerve (RLN) in laryngeal function?

Recurrent Laryngeal Nerve Supply and Functions

The recurrent laryngeal nerve (RLN) is a critical branch of the vagus nerve that carries motor fibers to all intrinsic laryngeal muscles except the cricothyroid muscle, and provides sensory innervation to the vocal folds, upper esophagus, and trachea, with injury resulting in significant voice, breathing, and swallowing impairments. 1

Anatomical Course and Origin

• The RLN originates from the thoracic portion of the vagus nerve, with the left and right nerves following different anatomical paths to reach the larynx 1
• The right RLN follows a more superficial course along the lateral esophageal edge, while the left RLN loops around the aortic arch and ascends in the tracheoesophageal groove in a deeper position 1
• Both nerves ultimately penetrate the cricopharyngeal membrane to innervate the laryngeal muscles 1
• Nonrecurrent laryngeal nerve is a rare variant (0.3-1.6%) observed more frequently on the right side, often in conjunction with an anomalous (retro-esophageal) right subclavian artery 1, 2

Functional Components and Innervation

• The RLN carries branchial efferents to the inferior constrictor, cricopharyngeus, and all intrinsic laryngeal muscles except the cricothyroid muscle 2
• Laryngeal motor fibers within the RLN have a 4 to 1 adductor to abductor ratio 2
• The RLN contains afferent fibers that mediate sensation from the vocal folds and below, including the upper esophagus and trachea 2
• In cases of extralaryngeal bifurcation (occurring in approximately 34% of RLNs), the motor fibers to the vocal cords are located exclusively in the anterior branches 3

Clinical Significance

Voice Function

• RLN injury causes immediate flaccidity of the ipsilateral vocal fold, loss of abduction and adduction, and severe dysphonia to complete paralytic aphonia 4
• Unilateral vocal fold immobility can significantly impact quality of life and may necessitate changing vocation 2
• Post-injury voice rehabilitation may require procedures such as Teflon injection, medialization thyroplasty, arytenoid adduction, or reinnervation by nerve transfer 4

Swallowing Function

• RLN injury frequently leads to aspiration of food and drink into the trachea due to compromised airway protection during swallowing 4, 1
• Unilateral vocal fold immobility is associated with significant dysphagia, most noticeably to liquids, and may lead to aspiration pneumonia 2
• Impaired ability to cough effectively in the early post-injury period further compromises airway protection 1

Respiratory Function

• Bilateral RLN injury presents a medical emergency due to potential complete airway obstruction 1
• Permanent bilateral vocal fold immobility may require tracheostomy or other airway interventions/glottic widening procedures 2

Surgical Considerations

• Critical anatomical landmarks for identifying the RLN during surgery include the Zuckerkandl tubercle and Berry's ligament 1
• The relationship between the RLN and inferior thyroid artery is highly variable and crucial for neural identification during surgery 1
• Risk of RLN injury is higher during thyroidectomy, with rates of 0.3-3% for permanent and 6-8% for transient damage 1
• Re-operative procedures carry a significantly higher risk of RLN injury (up to 30%) 1
• Detection of vocal fold paralysis doubles when patients undergo routine laryngeal examination after surgery compared to selective examination only in patients with persistent voice changes 2

Economic Impact of RLN Injury

• Post-thyroidectomy vocal fold immobility results in substantial costs including repeated office visits, laryngoscopic evaluations, voice therapy, and surgical interventions 2
• The economic impact of managing laryngeal disorders has been estimated to total between $179-295 million in annual direct costs 2
• The general impact of dysphagia within hospital settings is calculated to cost approximately $547 million each year 2