Microsurgical anatomy of the superior and recurrent laryngeal nerves

To study the microsurgical anatomy of the superior laryngeal nerve (SLN) and recurrent laryngeal nerve (RLN) with respect to anatomic landmarks, and to identify their vascular supplies.

The microsurgical anatomy of the anterior neck, the course of the right and left SLN and RLN and their variations were studied in 21 cadavers. Fresh cadavers were perfused with colored silicon dye to investigate the microvasculature in detail.

SLN originates from the inferior vagal ganglion at the C2 level and descends medially toward the thyrohyoid membrane. It branches into an external and an internal branch deep to the internal carotid artery at the C3 level. The external branch, along with the cricothyroid artery, descends deep to the superior thyroid artery toward the cricothyroid muscle. Accompanied by the superior laryngeal artery, the internal branch passes deep to the loop of the superior thyroid artery and pierces the thyrohyoid membrane. Both nerves reside in the fascia covering longus colli muscles and are supplied by their accompanying arteries. The loop of RLN is found at the T1-T3 level on the right, and more caudally at the T3-T6 level on the left, entering the larynx between C5-C7 levels on both sides. RLN receives arterial supply from the esophageal and tracheal branches of the inferior thyroid artery proximally, and by the inferior laryngeal artery distally.

Incidental intraoperative injury to the SLN and RLN potentially could be avoided by understanding the detailed course of each nerve with respect to the surrounding anatomic landmarks and by recognizing their blood supplies.