The blood supply to the thyroid gland is derived from which of the following arteries as the primary source?

Explanation

## Arterial Supply of the Thyroid Gland **Key Point:** The thyroid gland receives its primary blood supply from two main arteries: the superior thyroid artery (branch of external carotid) and the inferior thyroid artery (branch of thyrocervical trunk of subclavian artery). ### Primary Arterial Supply | Artery | Origin | Course | Supply | | --- | --- | --- | --- | | **Superior thyroid artery** | External carotid artery | Descends along superior pole of thyroid | Upper and medial portions of thyroid | | **Inferior thyroid artery** | Thyrocervical trunk (1st part of subclavian) | Ascends medially, enters lower pole | Lower and lateral portions of thyroid | | Thyroidea ima artery | Brachiocephalic trunk or aortic arch (variable, ~3%) | Ascends in midline | Isthmus and lower pole (when present) | ### Clinical Anatomy **High-Yield:** The superior thyroid artery is the first branch of the external carotid artery and is the largest arterial supply to the thyroid. The inferior thyroid artery is the largest branch of the thyrocervical trunk. **Clinical Pearl:** During thyroid surgery, the superior thyroid artery is ligated first to reduce blood loss, followed by the inferior thyroid artery. The recurrent laryngeal nerve runs posterior to the inferior thyroid artery and may be injured during ligation if not carefully identified. **Warning:** The thyroidea ima artery (when present) arises from the brachiocephalic trunk or aortic arch and ascends in the midline anterior to the trachea. It is clinically significant in tracheostomy and thyroid surgery as it may be encountered in the midline. ### Venous Drainage Thyroid veins drain into the superior and middle thyroid veins (→ internal jugular vein) and inferior thyroid veins (→ brachiocephalic vein). This is important to remember for thyroid surgery to prevent venous hemorrhage. **Mnemonic:** **SIT** — Superior (External carotid), Inferior (Thyrocervical trunk), Thyroidea ima (Brachiocephalic/aorta, variable).