Microsurgical anatomy of the laryngeal nerves as related to thyroid surgery

The objectives were to explore microsurgical anatomy of the superior and recurrent laryngeal nerves and their importance in thyroid surgery, and to examine areas of potential morbidity, means of identification, and arterial supply of the laryngeal nerves.

Descriptive analysis of anatomical features.

Twenty-one adult cadavers, some perfused with colored silicon, were dissected for the study project.

The right recurrent laryngeal nerve (RLN) branches off the vagus at the level of the subclavian artery and the left one at the level of the aorta. Both ascend parallel to the tracheoesophageal groove and innervate trachea, esophagus, and the inferior pharyngeal constrictors en route. The RLN has the highest probability to pass between the branches of the inferior thyroid artery on the right side and posterior to them on the left side. The RLN always passes posterior to the cricothyroid joint. The RLN is supplied by the branches of the inferior thyroid artery. The superior laryngeal nerve (SLN) branches into internal and external branches deep to the carotid bifurcation. The internal branch passes deep to the superior thyroid artery and descends toward thyrohyoid membrane. The external branch travels deep and parallel to the superior thyroid artery to innervate cricothyroid muscle. The internal branch is supplied by the superior laryngeal artery, and the external branch by the cricothyroid artery.

The only consistent location of the RLN is when it passes posterior to the cricothyroid joint. Because of extreme variability of the inferior thyroid artery and the RLN, it is suggested that the artery be ligated either proximally or at its tertiary branches on thyroid capsule. The internal branch of the SLN is not potentially at risk during thyroidectomy unless the superior thyroid artery is ligated proximally. The external branch of the SLN accompanies the superior thyroid artery for most of its course and is at potential risk if the trunk of the superior thyroid artery is ligated outside the pretracheal fascia.