EBSLN and Factors Influencing its Identification and its Safety in Patients Undergoing Total Thyroidectomy: A Study of 456 Cases.

BACKGROUND: The external branch of the superior laryngeal nerve (EBSLN) is at surgical risk during superior thyroid pole ligation during thyroidectomy. Majority of studies have addressed the identification of these nerves and its reported incidence. Very few studies have addressed the relationship of these nerves with the volume of the thyroid gland and presence of toxicity. MATERIALS AND METHODS: A retrospective evaluation of 456 patients who underwent total thyroidectomy were analysed from the prospectively maintained database. The EBSLN was diligently identified and preserved before individual ligation of the superior thyroid pedicle. The nerve was graded as per the Cernea classification (type I, IIa and IIb). Goitres are classified into toxic & non-toxic based on hyperthyroidism, further sub classified as large (>50 cc) and small (≤50 cc) based on volume of each lobe. The grading of EBSLN was correlated with hyperthyroidism and volume of each lobe. RESULTS: In 456 patients (912 nerves), EBSLN was identified in 849/912(93.09%), type I in 156/912(17.1%), type IIa in 522/912(57.23%) and type IIb in 171/912(18.75%). The prevalence of large goitres was 180/912(19.73%).Type IIb nerve was predominantly seen in 161/180(89.4%) of large goitres. Type IIb nerves was more common in toxic 141/372(37.9%) than non-toxic lobes 25/540(5.46%). CONCLUSION: Large goitres are not uncommon in toxic cases. The EBSLN is at highest risk of injury in this subgroup of patients and surgical expertise is essential to identify this entity of EBSLN to perform a safe thyroidectomy.