Identification of the external laryngeal nerve: Its anatomical relations to inferior constrictor muscle, superior thyroid artery, and superior pole of the thyroid gland in Thais

Abstract

Background: The external laryngeal nerve (ELN) is not routinely identified during thyroid surgery despite clear benefits from doing so. One reason is its anatomical variations, which differ from papers to papers. There were also very few studies of ELN in Thais, especially its relation to inferior constrictor muscle and tip of superior pole of the thyroid gland, which serve as important landmarks when identifying the ELN intra operatively. Objective: To describe the course of ELN and its relations to the inferior constrictor muscle, superior thyroid artery (STA), and tip of superior pole of the thyroid gland in Thais in order to serve as a guide for identification and preservation of the nerve. Material and Method: One hundred thirty four ELNs from 68 cadavers with normal-sized thyroid glands and no signs of neck abnormality were studied. Three areas were studied, (1) its relation to inferior constrictor muscle, (2) the nearest distance from the nerve to tip of the superior pole of the thyroid gland, and (3) the crossing point of the ELN and STA in relation to the tip of the superior pole of the thyroid gland. All distances were measured in mm using avernier caliper. Results: The three areas of the study were reported separately using established classifications and compared to the previous published papers. All ELNs run superficially, at the least on the upper portion of the inferior constrict muscle, rendering it more vulnerable to injury in Thais. Conclusion: The course of the ELN and its relations to nearby structures can vary considerably and are influenced by many factors. Nevertheless, these findings should encourage the surgeons to identify the ELN intraoperatively with meticulous dissection to minimize the risk of ELN injury.