Relation of the external branch of the superior laryngeal nerve to the superior pole of the thyroid gland: An anatomical study

Abstract

The external branch of the superior laryngeal nerve (ELN) is intimately associated with the superior thyroid artery (STA) in relation to the superior pole of the thyroid gland, rendering it vulnerable to injury during the ligation of this vessel during thyroidectomy. Although most texts acknowledge the fact that the nerve is in close relation to the STA, there has not been an anatomical study to relate the position of the ELN to the superior pole of the thyroid gland. The aim of this study was to determine the shortest distance, from the most superior point of the thyroid gland, to the ELN. Bilateral micro-dissection on 43 adult cadavers, excluding those with thyroid pathology and previous thyroidectomies, was undertaken. The most superior point of the superior pole of the thyroid gland was identified and the shortest distance to the ELN was measured with a digital calliper (accuracy 0.01 mm). The metric study indicated a mean distance from the ELN to the superior pole of a normal sized thyroid gland of 5.76 mm (range: 2.00-11.26) on the right, and 6.17 mm (range: 2.78-13.48) on the left. From the literature, it is clear that the ELN may even be closer to the superior pole of an enlarged thyroid gland. The recommendation to stay on the substance of the superior pole of the thyroid gland when ligating the STA remains valid, as the nerve is extremely close in relation to the superior pole of the normal thyroid gland.

Relações do ramo externo do nervo laríngeo superior com a artéria tireóidea superior: estudo em 101 nervos

“…Our results, which identified one case (0.99%) of ESLN at that location, are statistically comparable to those obtained by Naidoo 20 , who does not describe the nerve in that position at all. Thus, the results much differ from those published by Cernea 14 Therefore, based on those authors 12,14,18,19 , supported by the results obtained by them, the previous identification of the ESLN is recommended before the ligation of the superior thyroid artery in thyroidectomies, in order to prevent iatrogenic injuries.…”

“…However, because the differences between the findings by Cernea 12,14 , Furlan and Kierner 19 and the data obtained in the present study, as well as in Naidoo's 20 , are statistically significant and do matter in the context of a specific surgical decision -whether or not to identify the ESLN prior to the ligation of the superior thyroid artery -, it is necessary to take them into careful consideration.…”

Proposal for anatomical classification of the superior pole in thyroid surgery

“…In an anatomical review, Naidoo and co‐workers concluded that it is better to stay on the substance of the superior pole of the thyroid gland when ligating the superior thyroid artery, as the nerve is extremely close in relation to the superior pole of the normal thyroid gland . This is mainly relevant in Type 2 and 3 according to our proposed classification.…”

The Human Cricothyroid Muscle: Three Muscle Bellies and Their Innervation Patterns

“…To prevent the ESLN from injury during neck surgery, investigators have made great efforts to determine its course in the neck and relations to the thyroid gland and superior thyroid artery. 21,22 However, little is known about the intramuscular branching of the ESLN within the CT muscle.…”