Objective: To establish the frequency and degree of postthyroidectomy injury of the external branch of the superior laryngeal nerve (EBSLN) by means of electromyography and to assess whether intraoperative identification of the nerve and the presence of malignancy influence morbidity.
Patients and methods: Prospective, randomized, blind study. Comparison of 100 superior thyroid poles subjected to surgery because of benign and malignant disease, divided in three groups: G1, thyroidectomies, without searching for the EBSLN; G2, thyroidectomies, searching for the EBSLN; G3, Control, lobes, contralateral to the lobectomy, not surgically manipulated. The electromyographic function of the EBSLN was assessed in all cases, classifying the degree of injury and clinically assessing its function. Central tendency measures were used, as well as X (2) and multiple variance analysis.
Results: In G1, with 50 dissections of the superior pole, 25 injuries were found in 15 patients (10 bilateral and 5 unilateral). In G2, EBSLN injury was found after 13 explorations of the superior pole in 8 patients (5 bilateral and 3 unilateral). G3 patients did not present EBSLN injury. X (2) among groups and degree of injury revealed that intraoperative identification of the EBSLN decreases its injury. No evidence were found that injury frequency is increased by the presence of thyroid malignancy, extracapsular infiltration, or size of tumor. Clinical manifestations of hoarseness were present in 14% of G1 patients and 8% of G2 patients.
Discussion: The rate of EBSLN injury increased when not exploring and/or identifying it expressly. The presence of cancer, extracapsular extension, or size of the thyroid tumor exerted no influence on the frequency of injury; localization of the nerve was the only factor affecting injury. Hoarseness correlated with the degree of injury.
Conclusion: EBSLN must be localized expressly to decrease the risk of injury.