Surgical anatomy of the external branch of the superior laryngeal nerve.

Iatrogenic lesions of the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomies are not infrequent due to the possibility of anatomic variations of the relationships of this nerve with the superior thyroid vessels. Therefore, based on an anatomic analysis of 30 superior thyroid poles from 15 fresh cadavers, a new classification of the EBSLN was proposed, considering the jeopardy during a thyroidectomy. Thirty-seven percent of the nerves were type 2, ie, crossing the superior thyroid pedicle less than 1 cm above the superior thyroid pole. It is notable that 20% were type 2b, ie, crossing the vessels below the upper border of the pole, having been considered "high risk." This incidence was comparable with other series, which found dangerous anatomic variations of the EBSLN in the range of 15% to 68%, confirming that a significant proportion of these nerves might be at risk during surgery on the superior thyroid pole.