Background: To determine whether the insertion of the sternothyroid muscle onto the oblique line of the thyroid cartilage can be used to reliably locate the external branch of the superior laryngeal nerve (EBSLN) during thyroidectomy.
Methods: This is a prospective descriptive case series. The EBSLN was identified and confirmed with a nerve stimulator during thyroid surgery. The entry point of the EBSLN into the inferior constrictor/cricothyroid muscle was measured in relation to the insertion and anterior border of the sternothyroid muscle. The perpendicular distance from the insertion of the sternothyroid muscle onto the oblique line was designated the vertical distance (VD) of the nerve entry point (NEP), and the perpendicular distance from the anterior border of the sternothyroid muscle was designated the horizontal distance.
Results: Ninety patients underwent 130 thyroid lobectomies (60 female, 30 male) (mean age 53.5 years, range, 18-91 years). An attempt to identify the nerve was made in 127 thyroid lobectomies. The EBSLN was identified in 111 cases (87.4%). The mean VD of the NEP from the muscle insertion was 1.1 mm (SD 1.1 mm, range, 0-5 mm) and the mean horizontal distance (HD) was 9.5 mm (SD 3.8 mm, range, 2-21 mm).
Conclusions: The EBSLN muscle entry point usually lies 1.1 mm from the sternothyroid insertion onto the oblique line, and 5-12 mm from the anterior border of the muscle. These useful landmarks allow the nerve to be consistently located, identified and preserved during thyroid surgery prior to ligating the superior thyroid vessels.
Keywords: Laryngeal nerve; surgical landmark; thyroidectomy.
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