Relation between the external branch of the superior laryngeal nerve and the superior thyroid artery: a study in 101 nerves.

OBJECTIVE This paper aims to propose a protocol with the topographical relations of the ESLN and the superior thyroid artery in order to minimize the number of flaws in the proposals found in the literature. METHODS the cervical regions of 57 human cadavers from the Forensic Medicine Institute were dissected bilaterally, with photographic identification of the ESLNs and their relation to the superior thyroid artery. These data were used to propose the following classification: Type 1: unidentified ESLN; Type 2: the ESLN crosses the superior thyroid artery 1.5 cm above the upper pole of the thyroid gland; Type 3: the ESLN crosses the superior thyroid artery between 1 and 1.5 cm above the upper pole of the thyroid gland; Type 4: the ESLN crosses the superior thyroid artery less than 1cm above the upper pole of the thyroid gland; Type 5: the ESLN crosses lateral-medially below the upper pole of the thyroid gland. As a supplement, types 2, 3 and 4 received the subclassification: A - the ESLN was partially or totally enclosed in the perimuscular or intramuscular areolar connective tissue, in the inferior pharyngeal constrictor muscle, in more than half of its path after crossing the superior thyroid artery; B - the ESLN was not enclosed in either of these tissues. RESULTS Type 1, 11.88%; Type 2, 13.86%; Type 3, 34.65%; Type 4, 38.61%; Type 5, 0.99%. CONCLUSION the majority of the ESLN nearest to the upper pole of the gland (types 3 and 4) followed the perimuscular or intramuscular superficial connective tissue in the upper pole of the thyroid gland, which, in this study, disobliges the systematic identification of the nerve in thyroidectomies (p=0.075).