This nerve is extremely important in thyroid surgery, indeed the most important structure in thyroid surgery, as damage can leave patients unable to speak and potentially requiring tracheostomy.
The length of the RLN from vagal takeoff to laryngeal entry point is 8.5 cm on the right and 10 cm on the left. this result in discrete different evoked monitoring waveform latencies which allow recognition of the nerve being stimulated providing clear documentation of neural function.
The nerve is WHITE and approximately 2mm wide.
The normal RLN virtually always has a vessel running on its surface (vasa nervosum), seen as a ventral “red strip.”
The recurrent laryngeal nerve contains 2-4 times as many adductor to abductor fibres.
On the Left arise from the vagus nerve just below the aortic arch. Its fibres are situated anteriorly in the vagus nerve and then begin to rotate medially until they seperate themselves just below the aortic arch (on the left)
The recurrent laryngeal nerves are dragged down by the lowest persisting aortic arch.
Right - subclavian artery - 4th brachial arch.
Left = Ligamentum
Right = R-tery (subclavian)
On the right side since the recurrent laryngeal nerve approaches the traceoesophageal groove more laterally.
Hooks around the arch lateral to the ligamentum arteriosum (embryological remnant of ductus arteriosus) and then passes internally.
Then passes along Tracheoesophageal groove.
Approaches the medial surface of the thyroid gland from below.
The right vagus crosses over the 1st part of the subclavian artery anteriorly.
Arises in front of the subclavian artery.
Passes posteriorly around the artery.
Runs medially along the pleura.
Passess caudal behind the right common carotid.
Then passes obliquely to lie lateral to the trachea.
Associated (normally posterior to the inferior thyroid artery).
Then ascends in the tracheoesophageal groove.
Lies very close behind the pretracheal fascia of the thyroid gland.
Passess deep to the inferior constrictor with the inferior laryngeal vessels.
Lies immediately behind cricothyroid joint.
Reaches the lower border of the piriform recess.
Then penetrates the laryngeal wall.
Inside the larynx Normally divides into a sensory and motor branches.
Intra-laryngeal branches between 3 and 7, most commonly 4-5.
HISHAM: 60% tracheoesophageal groove. 5% lateral to the trachea. 28% directly posterior to thyroid lobe.
Between 25-75% of recurrent laryngeal nerves divided at or even below the inferior border of the cricoid cartilage (aka the border for the larynx).
Up to five branches have been described.
Literature doesn't distinguish between "true laryngeal bifurcation" and bifurcation to other structures: trachea (sensory), esophagus (sensory and motor), inferior constrictor (sensory and motor), and sympathetic chain, and the typically larger branches arising as a terminal division of the nerve destined to innervate laryngeal musculature.
Serpell: 50% to 60% of patients have some small branches of the RLN to the trachea, esophagus, or inferior constrictor, but only 20% to 30% have true RLN extralaryngeal branches that enter the larynx and with stimulation resulting in laryngeal EMG activity.
Most common extralaryngeal branching pattern is to bifurcate. The anterior branch of the division contains the motor fibres. (Serpell).
Any extralaryngeal branches usually exist at the level of the ligament of Berry and are usually not present below the inferior thyroid artery (only 10% below this). The lack of branches below the inferior thyroid artery is part of the rationale for the inferior approach to the RLN in the thoracic inlet as described by Lore.
Non recurrent Laryngeal Nerve - courses lateral to medial to peirce thr cricothyroid membrane from the carotid sheath, less than 1%.
Its presence is associated with an aberrant subclavian artery (subclavian artery from the distal aortic arch) and the developmental absence of the brachiocephalic trunk.
A retroesophageal subclavian artery (on neck computed tomography) virtually assures (and is associated with) a non-recurrent laryngeal nerve.
Relationship to the inferior thyroid artery - discussed in the inferior thyroid artery post.
Left RLN more Likely, to Lie behind the ITA.
Right also enters the tracheoesophgeal groove more laterally
2. Thoracic Inlet - right is much more lateral.
3. Right is more anterior in the tracheal region. Classically, the right recurrent laryngeal nerve more frequently presents a prevascular course than the left recurrent laryngeal nerve, as it arises higher than the left nerve and has a more oblique course.
4. Right is more oblique in the paratracheal region.
1. Sends branch to the cardiac plexus -> given off as it hooks around the subclavian artery.
2. Afferent fibres for mucosa of the trachea (pain) + parasympathetic (uncertain significance)
3. Oesophagus as it ascends in the tracheo-osaphgeal groove.
4. May innervate inferior constrictor (but normally this is done by pharyngeal plexus)
> **Surgical Anatomy**
- The majority of RLNs are located within 3mm of Berry’s ligament; rarely the nerve
is embedded in it (one study showed 30% of cases)*, and more commonly lies posterio-laterally to it (another study 97%).
In 10% of Berlin's dissections, the RLN actually penetrated the thyroid gland that had infused and was present within the ligament of Berry - This prohibits capsular dissection as a method to prevent recurrent laryngeal injury.
Classically, the RLN is identified intraoperatively in Simon’s triangle, which is formed by the common carotid artery laterally, the oesophagus medially, and the ITA superiorly.
Tubercle of Zukerkandl - Generally courses between this and the trachea. 98% of patients had RLN medial to the tubercle!
When thyroid tissue is present as a posterior lateral projection of the lateral thyroid lobe, it can be termed the tubercle of Zuckerkandl. When present in its typical position, the tubercle is caudal to the ligament of Berry (LOB)
A neural anastomosis.
posterior RLN fibers join posterior most branch of internal branch of SLN this happens over the posterior surface of the posterior cricoarytenoid muscle (controversy about whether the internal laryngeal nerve has motor fibres) 100% of people studies.
B. Human Communicating Nerve
Sanudo et al. found that in 68% of 90 human microdissected specimens, the external branch of the SLN, after innervating the cricothyroid muscle, continues on, extending through the cricothyroid membrane to innervate the anterior thyroarytenoid muscle region