The inferior non recurrent laryngeal nerve: a major surgical risk during thyroidectomy.

It is now widely established that systematic intraoperative location and diligent dissection of the recurrent inferior laryngeal nerve during thyroidectomy are the keystones to assure its anatomic and functional preservation. The possibility of abnormal routes, like a non-recurrent cervical course of the inferior laryngeal nerve is an additional major argument for its systematic identification to avoid surgical damage. In 2517 cervicotomies performed between 1992 and 1997 for at least right thyroid lobe excision or parathyroid glands exploration, 20 cases of non recurrent laryngeal nerve were identified (0.79%). The embryological nature of such a nervous anatomical variation results originally from a vascular disorder, named arteria lusoria in which the fourth right aortic arch is abnormally absorbed, being therefore unable to drag the right recurrent laryngeal nerve down when the heart descends and the neck elongates during embryonic development. The surgeon must be aware of the possibility of a non recurrent laryngeal nerve, which arises directly from the cervical vagus and therefore represents a severe potential pitfall during thyroidectomy. Given the absence of reliable clinical symptoms and signs or investigations indicating preoperatively the possibility of a non recurrent nerve, guidelines are given to prevent intraoperatively this major surgical risk.