Thyroid Gland Blood Supply : Mnemonics

Arterial supply

1. Superior thyroid artery (branch of ECA): Supplies Upper 1/3 of lobes + Upper 1/2 of isthmus
2. Inferior thyroid artery (branch of thyrocervical trunk of Subclavian artery): Supplies Lower 2/3 of lobes + Lower 1/2 of isthmus + Parathyroid glands (by ascending branch)
3. Thyroidea ima artery (only in 10%): from aortic arch or brachiocephalic trunk
4. Accessory thyroid arteries: from tracheal and esophageal arteries

Arterial anastomosis

1. Anterior aspect (at the upper border of isthmus): Between anterior branch of superior thyroid artery of 2 sides
2. Posterior aspect: Between posterior branch of Superior thyroid artery and inferior branch of Inferior thyroid artery

Venous drainage

1. Superior thyroid vein: drains into IJV
2. Middle thyroid vein: drains into IJV
3. Inferior thyroid vein: drains into left Brachiocephalic vein
4. Fourth thyroid vein (of Kocher): may emerge between middle and inferior thyroid veins and drain into the IJV

The venous plexus lies beneath the true capsule (peripheral condensation of fibrous stroma of gland). Hence, during thyroidectomy, thyroid gland is removed along with the true capsule to avert the hemorrhage. False capsule (pre-tracheal fascia) is left intact.

Thyroid Arteries and Laryngeal Nerves

Mnemonic: SEEN InTRA

1. Superior thyroid artery
   • External carotid artery
   • External laryngeal nerve is closely related
   • Near the gland – superior thyroid artery is relatively far from external laryngeal nerve and hence ligated here (mnemonic: to the thyroid I go)
2. Inferior thyroid artery
   • Thyrocervical trunk
   • Recurrent laryngeal nerve is closely related
   • Away from the gland – inferior thyroid artery is relatively far from recurrent laryngeal nerve and hence ligated here (mnemonic: away from thyroid I flee)