The superior laryngeal nerve in thyroid surgery.

Injury to the external branch of the superior laryngeal nerve (ESLN) during thyroid surgery can have serious consequences. A strategy for perioperative identification and preservation of the ESLN was clinically evaluated after postmortem anatomic observations. These showed that 20% of ESLNs run distally through the pharyngeal constrictor muscle, which necessitates intramuscular dissection for identification in the area around the superior thyroid pole. In 23% of the ESLNs identifiable without intramuscular dissection (18% of the total), a course partly lateral to the superior thyroid artery and its branches implied definite risk of injury during division of the superior pole vessels. In the clinical series, 72% of the ESLNs were identifiable without intramuscular dissection, and 19% of these (14% of the total) were partly lateral to the superior thyroid artery. Only one patient had signs of ESLN injury postoperatively, probably caused by diathermy to an adjacent vessel. Perioperative identification of ESLN with dissection into the pharyngeal constrictor muscle (about 20% of cases) appears to be inadvisable, but identification of ESLN with other courses is important, as around 20% are highly vulnerable during division of the superior thyroid artery and its branches.