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The left recurrent laryngeal nerve or nervus laryngeus recurrens sinister in Latin arises from the left vagus nerve (CN X) in the thorax. It loops around the inferior margin of the arch of aorta, just lateral to the ligamentum arteriosum at vertebral level T4-T5. It then ascends superiorly to the posteromedial aspect of the thyroid gland, usually behind the terminal branches of the inferior thyroid artery. It must be noted that the right recurrent laryngeal nerve travels directly upwards, looping around the subclavian artery. Therefore, the two recurrent laryngeal nerves are not symmetrical.
The recurrent laryngeal nerves tend to nestle in a groove that lies between the trachea and the esophagus. The left recurrent laryngeal nerve then continues superiorly to enter the neck and terminate in the larynx. It supplies both the trachea and esophagus and all the intrinsic muscles of the larynx as well, except for the cricothyroid (innervated by the external laryngeal nerve). This permits the opening and closure of the vocal cords.
Because of its longer course, lesions of the left recurrent laryngeal nerve are more likely to happen compared to those of the right. The lesions are usually unilateral and can lead to isolated paralysis of all the laryngeal muscles on the affected side except for the cricothyroid. The patient may be asymptomatic or have a hoarse breathy voice, where they are unable to manipulate their pitch. This may be permanent or may lessen with time as the contralateral cord develops the ability to compensate the paralyzed side, though full restoration of the voice quality is seldom. Temporary aphonia (loss of voice) and laryngeal spasm may occur as well.
These lesions often result from cancer of the larynx and thyroid gland. They also can result from pressure of accumulated blood and serous exudate after operation, or from surgery itself on one of these structures: thyroid gland, neck, esophagus, heart, and lungs.
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