The recurrent laryngeal nerve branches from the vagus nerve (cranial nerve X). It has a distinctive pathway, playing a role in controlling various functions related to the throat. Its unique course makes it a subject of interest in both anatomy and clinical practice.
The Nerve’s Distinctive Path
The recurrent laryngeal nerve earns its name from its “recurrent” pathway, meaning it travels in the opposite direction to its branching point. Unlike most nerves that proceed directly to their target, it descends into the chest before looping back up towards the larynx.
The journey of the left and right recurrent laryngeal nerves differs significantly. The right recurrent laryngeal nerve branches from the vagus nerve around the first or second thoracic vertebra (T1-T2). It then loops under and behind the right subclavian artery, an artery located beneath the collarbone, before ascending back into the neck. This path is relatively shorter than its counterpart.
In contrast, the left recurrent laryngeal nerve has a much longer course. It branches off the vagus nerve at the aortic arch, which is the main artery curving over the heart. The nerve passes in front of the arch, then wraps underneath and behind it, often looping near the ligamentum arteriosum. Both nerves then ascend through a groove between the trachea and esophagus, eventually reaching the larynx.
Crucial Role in Voice and Breathing
The recurrent laryngeal nerve plays a fundamental role in voice production and airway management. It provides motor innervation to almost all intrinsic muscles of the larynx, also known as the voice box, with the exception of the cricothyroid muscle. These muscles control the movement and tension of the vocal cords.
The coordination of these laryngeal muscles allows for the wide range of vocalizations. For example, the posterior cricoarytenoid muscles, innervated by this nerve, are the only muscles capable of opening the vocal cords for breathing. Other muscles controlled by the nerve work to close and adjust the tension of the vocal cords, enabling the modulation of pitch, volume, and tone during speech and singing.
Beyond voice, the nerve also protects the airway. Its control over vocal cord movement ensures the vocal cords close effectively during swallowing, preventing food or liquids from entering the trachea and lungs. The recurrent laryngeal nerve also provides sensory innervation to the larynx below the vocal cords, contributing to protective reflexes like coughing.
Vulnerability and Impact of Damage
The distinctive and extended path of the recurrent laryngeal nerve, particularly the left side, makes it susceptible to injury from various medical conditions and procedures. Its close proximity to major structures in the neck and chest means it can be affected during surgery. For instance, thyroidectomy, which involves surgery on the thyroid gland, carries a risk of recurrent laryngeal nerve injury. The risk can be higher in re-operations or for malignant thyroid conditions.
Cardiac surgery, especially procedures involving the aortic arch, also poses a risk to the recurrent laryngeal nerve due to its anatomical relationship with the heart and great vessels. Injuries can also occur from neck trauma, infections, or tumors in the neck or chest. A Pancoast tumor, located in the apex of the lung, or other neck tumors can compress the nerve, leading to dysfunction.
Damage to the recurrent laryngeal nerve can result in a range of symptoms, primarily affecting the voice. Unilateral injury, affecting one nerve, commonly causes hoarseness, a breathy voice, or changes in vocal pitch. This occurs because one vocal cord may become paralyzed or have restricted movement, impacting its ability to meet the other vocal cord for normal sound production. Patients might also experience noisy breathing or difficulties swallowing liquids.
More severe consequences arise if both recurrent laryngeal nerves are damaged, though this is less common. Bilateral vocal cord paralysis can lead to significant breathing difficulties, including noisy breathing (stridor) and airway obstruction, as the vocal cords may not open sufficiently for airflow. Swallowing difficulties (dysphagia) and the risk of aspiration, where food or liquid enters the lungs, are also potential complications of both unilateral and bilateral injuries.