Anatomical variations of the external branch of the superior laryngeal nerve in relation to the inferior constrictor muscle: cadaveric dissection study

Objectives: To determine anatomical variations in the external branch of the superior laryngeal nerve in relation to the inferior constrictor muscle, and to propose a rational approach for the preservation of the nerve in thyroid surgery based on anatomical principles. Method: A cadaveric dissection study of the anatomy of the external branch of the superior laryngeal nerve in relation to the inferior constrictor muscle was conducted. Twenty-nine formalin-fixed cadavers of both sexes (age 50-70 years), with normal necks, were examined. Results: In relation to the Friedman classification, three anatomical variations of the external branch of the superior laryngeal nerve were found. Type 1 variation was found in 57.1 per cent of cases, type 2 in 26.8 per cent and type 3 in 16 per cent. Conclusion: The prevalence of type 3 variation of the external branch of the superior laryngeal nerve suggests that the nerve will not be encountered in a certain percentage of individuals as it lies under the cover of the inferior constrictor. Therefore, there is no justification for attempting to identify the nerve in all cases.