Anatomy of the Recurrent Laryngeal Nerve
The recurrent laryngeal nerve (RLN) is a mixed nerve with sensory and motor fibers that originates from the thoracic portion of the vagus nerve and follows distinct anatomical paths on each side of the body to innervate the intrinsic muscles of the larynx. 1
Origin and Course
The RLN branches from the vagus nerve (CN X) in the thorax and follows different paths on the right and left sides:
Right RLN: Lies in a more superficial plane along the lateral esophageal edge. It loops around the subclavian artery before ascending toward the larynx. 1
Left RLN: Loops around the aortic arch and is located more deeply in the tracheoesophageal groove as it ascends. 1
Both nerves then travel upward within the lateral peritracheal loose connective tissue, with the left RLN typically positioned closer to the tracheoesophageal groove than the right. 2
Terminal Course and Entry into Larynx
As the RLNs approach the larynx, they:
- Travel as 2-3 mm thick compact cords that follow a sinuous path upward 2
- Give off 8-14 branches to both the esophagus and trachea 2
- Enter the larynx laterocaudal to the cricopharyngeus muscle 2
- Penetrate the cricopharyngeal membrane to innervate the laryngeal muscles 1
Branching Pattern
The RLN may present as:
- A single segment
- Multiple branches (up to five) 1
The anterior extralaryngeal branches typically contain motor fibers that can be stretched during dissection of Berry's ligament. 1
Important Anatomical Landmarks
Key landmarks for identifying the RLN include:
- Zuckerkandl tubercle: A bulge of thyroid tissue from the lateral thyroid lobe 1
- Inferior thyroid artery (ITA): Has highly variable relationships with the RLN 1
- Berry's ligament: A posteromedial thickening of perithyroid fascia that is adherent to the thyroid capsule and difficult to dissect 1
Innervation Function
The RLN provides:
- Motor innervation to all intrinsic laryngeal muscles except the cricothyroid muscle (which is innervated by the external branch of the superior laryngeal nerve) 1
- Sensory innervation to the vocal folds and the area below, including the upper esophagus and trachea 1
The motor fibers within the RLN have a 4:1 adductor to abductor ratio. 1
Anatomical Variations
Non-recurrent Laryngeal Nerve
- Incidence: 0.3-1.6% of cases, more common on the right side 1
- Types:
- Type I: Originates from vagus nerve above the laryngotracheal junction and descends into larynx
- Type II: Arises from vagus nerve below the laryngotracheal junction and runs parallel to the inferior thyroid artery 1
- Associated anomaly: Often occurs with an anomalous (retro-esophageal) right subclavian artery 1
Extralaryngeal Branching
Precocious division of RLN extralaryngeal branches is a common anatomical variation that can complicate surgical identification. 1
Clinical Significance
Injury to the RLN can result in:
- Unilateral damage: Hoarseness and voice changes due to vocal fold paralysis 1
- Bilateral damage: Stridor and potential airway obstruction requiring tracheostomy 1
The RLN is particularly vulnerable during thyroid surgery, with injury rates of 0.3-3% for permanent damage and 6-8% for transient injury. 1
Dual Innervation
An important anatomical feature is that both the RLN and superior laryngeal nerve supply the same laryngeal muscles and mucosa, which may provide some compensatory function following RLN injury. 2, 3
Surgical Considerations
- Visual identification of the nerve during surgery is critical to prevent injury
- Knowledge of the variable relationship between the RLN and inferior thyroid artery is essential
- Awareness of potential anatomical variants, particularly non-recurrent laryngeal nerve
- Recognition that the nerve pattern becomes unpredictable underneath the thyroid gland 2
Understanding the detailed anatomy of the RLN is crucial for surgeons operating in the neck region, particularly during thyroidectomy, to minimize the risk of iatrogenic injury and subsequent vocal fold paralysis.