Variations of the origin of superior thyroid artery and its relationship with the external branch of superior laryngeal nerve

INTRODUCTION: The superior thyroid artery, the main atrial supply of neck region, is branched from the external carotid artery as a first branch, but it may also arise from the common carotid artery and its bifurcation. The external branch of superior laryngeal nerve runs parallel to it and later crossing the artery either above or below the upper pole of the thyroid gland. OBJECTIVE: This study aimed at evaluating the variations of the origin of superior thyroid artery and its relationship with the external branch of the superior laryngeal nerve. METHODS: A descriptive study was conducted on 43 embalmed cadavers. The anterior triangle of the neck region was dissected bilaterally. The presence or absence of STA and its origin, branching pattern, relationship with the external branch of the superior laryngeal nerve, level of origin in relation to the lamina of the thyroid cartilage and level of carotid bifurcation were observed and recorded. RESULT: The superior thyroid artery arises from the external carotid artery in 44.2%, common carotid bifurcation in 27.9% and common carotid artery in 26.7% of cadavers. In one of the cadaver, the superior thyroid artery arises from lingual artery. The origin of superior thyroid artery was significantly associated with its branching pattern and level of common carotid artery bifurcation. The mean distance from the upper pole of the thyroid gland to the level where an external branch of superior laryngeal nerve turns medially from superior thyroid artery was found to be 1.04cm. CONCLUSION: The wide range of variations of the superior thyroid artery on its origin and relationship with adjacent structures is a common phenomenon. The clinicians should be aware of those variations.