Corpus: Recurrent laryngeal nerve

The recurrent laryngeal nerve, or RLN for short, is a paired branch of the vagus nerve. The section of this nerve closest to the larynx is also referred to as the inferior laryngeal nerve.

The special visceromotor fibers of the recurrent laryngeal nerve originate from the nucleus ambiguus and emerge from the brainstem alongside the cranial root of the accessory nerve. These fibers then join the vagus nerve at the jugular foramen after crossing as the internal ramus. The sensory nerve fibers have their cell bodies in the inferior ganglion of the vagus nerve (ganglion nodosum) and project to the nucleus solitarius. The parasympathetic fibers of the recurrent laryngeal nerve originate from neurons in the dorsal nucleus of the vagus nerve.

The course of the recurrent laryngeal nerve differs between the right and left sides of the body.

The left recurrent laryngeal nerve originates in the upper mediastinum and loops around the aortic arch. It then ascends through the esophagotracheal groove, situated between the esophagus and trachea, to reach the larynx.

The right recurrent laryngeal nerve emerges from the vagus nerve at the superior thoracic aperture, loops around the right subclavian artery, and then ascends alongside the trachea in the esophagotracheal groove to the larynx.

On both sides, the nerve crosses the inferior thyroid artery before entering the larynx posteriorly between the cricoid cartilage and thyroid cartilage, penetrating the constrictor pharyngis medius muscle.

The recurrent laryngeal nerve gives off the following branches:

• Esophageal branches: Supplying the cervical portion of the esophagus.
• Tracheal branches: Supplying the cervical section of the trachea.

The final branch of the recurrent laryngeal nerve is the inferior laryngeal nerve, which forms an anastomosis with the superior laryngeal nerve known as the Galen anastomosis.

Some texts also describe additional inferior cardiac nerves that connect to the sympathetic trunk and run to the cardiac plexus.

In rare cases (about 1 in 200), the right recurrent laryngeal nerve does not loop around the right subclavian artery. Instead, it branches off from the vagus nerve near the level of the cricoid cartilage. This anatomical variation is often associated with an aberrant right subclavian artery, which arises from the aorta on the left side and passes behind the esophagus to the right side.

The looped course of the recurrent laryngeal nerve is due to the descent of the heart into the thorax during embryonic development. It is associated with the 6th pharyngeal arch.

The recurrent laryngeal nerve innervates nearly all the intrinsic muscles of the larynx, except for the cricothyroid muscle. These include:

• Posterior cricoarytenoid muscle
• Lateral cricoarytenoid muscle
• Transverse arytenoid muscle
• Oblique arytenoid muscle
• Thyroarytenoid muscle

These muscles control the opening and closing of the glottis by abducting and adducting the vocal folds, playing a crucial role in voice production (phonation) and breathing.

The sensory fibers of the recurrent laryngeal nerve supply the mucous membrane of the larynx below the glottis (subglottic space).

Parasympathetic fibers from the vagus nerve also innervate the tracheal glands in the upper trachea, regulating secretion production.

Damage to the recurrent laryngeal nerve, known as recurrent nerve palsy, can result from thyroid surgery, other operations in the neck, or conditions such as mediastinal tumors, Pancoast tumors, and aortic aneurysms.

• Unilateral paralysis typically presents as hoarseness.
• Bilateral paralysis can lead to severe dyspnea, as both sides of the glottis may be compromised.

• Waldeyer et al. Human anatomy: Textbook and Atlas in One Volume (De Gruyter Studium) (19th totaly rev. ed.), De Gruyter, 2012