Thyroid Gland

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The thyroid gland is an endocrine gland located in the anterior neck that wraps around the superior tracheal rings and cricoid cartilage. It has a rich blood supply so it can release the hormones it produces to increase metabolism. Embryological development of the thyroid begins at the floor of the pharynx before it passes down the thyroglossal duct. 

Gross Anatomy

The thyroid gland lies between the C5 and T1 vertebrae and consists of two pear shaped lateral lobes, connected by an isthmus that crosses anteriorly over the second and third tracheal cartilages. A pyramidal lobe that projects superiorly from the isthmus is often present. The thyroid gland is in the visceral compartment of the neck along with the trachea, oesophagus and pharynx, contained within the pretracheal fascia. This fascia tethers the thyroid gland to the trachea and larynx, which explains why the thyroid gland moves with the larynx on swallowing. These organs lie deep to the sternothyroid, omohyoid and sternohyoid muscles. The carotid sheath lies posterolaterally to the lobes of the thyroid gland. The isthmus is located anteriorly to the trachea and posteriorly to the pretracheal fascia.


During development the thyroid gland forms at the floor of the pharynx near the tongues' base. The thyroid gland then migrates down the thyroglossal duct to its adult location by seven weeks, the duct usually disappears during development but remnants of the thyroglossal duct can remain as a cyst or fistula. The foramen cecum on the tongue marks the origin of the thyroglossal duct. Additional functional thyroid tissue can remain anyway along the path of the thyroids' migration during development, including a lingual or pyramidal lobe.


The thyroid gland consists of follicles filled with colloid which take up iodine to make the thyroid hormones thyroxine and triiodothyronine, which increase metabolic activity in most of the body. Follicular cells arranged in a single layer surround follicles and secret thyroid hormones. The parafollicular cells of the thyroid gland secrete thyrocalcitonin which acts to lower serum calcium levels.


The superior and inferior thyroid arteries are major arteries that supply the thyroid gland. The superior thyroid artery originates as the first branch of the external carotids and descends to the superior pole of the lateral lobe where it divides into anterior and posterior glandular branches. The inferior thyroid artery is a branch from the thyrocervical trunk, which is the first branch of the subclavian artery. The artery ascends to the inferior pole of the lateral lobe where it supplies the posterior, inferior parts of the thyroid gland. In around 10% of individuals a thyroid ima artery that arises from the brachiocephalic trunk or aortic arch ascends to supply the anterior surface and isthmus of the thyroid gland.


Three veins form a venous plexus which drains the thyroid gland. The area of the thyroid supplied by the superior thyroid artery is primarily drained by the superior thyroid vein and the remaining area is drain by the middle and inferior thyroid veins. Both the superior and middle thyroid veins drain into the internal jugular vein and the inferior thyroid vein drains into the brachiocephalic vein.


Innervation to the thyroid is from the superior, middle and inferior cervical sympathetic ganglion via branches of the sympathetic trunk. These nerves do not stimulate the endocrine secretion of the thyroid gland, this is regulated by hormones from the anterior pituitary gland. The lymphatic drainage of thyroid gland is mostly into deep cervical nodes and some drainage into paratracheal nodes.

Clinical Anatomy

Thyroid goitre - A goitre is a diffuse enlargement of the thyroid  gland that has many causes including iodine deficiency and immunological disease. A common cause of an irregular goitre is a multinodular goitre consisting of hypertrophic areas and colloid cysts. These can be medically managed or surgically excised if the goitre is large enough to cause serious problems including respiratory obstruction. The sternothyroid muscle limits upward expansion of the thyroid gland, therefore it is common for the thyroid gland to expand posterior to the sternum when a goitre forms. These retrosternal goitres can compress veins as well as the trachea.


Thyroglossal cysts - These are fibrous cysts that can develop from remnants of any thyroid tissue left along the thyroglossal duct during development. These can be excised by surgery.


Recurrent laryngeal nerve trauma - The two recurrent laryngeal nerves arise from the vagus nerves and descend into the chest where the right nerve hooks around the subclavian artery, and the left nerve hooks around the aortic arch. They then ascend up the neck between the oesophagus and trachea before passing posterior to the thyroid gland to innervate the larynx. Due to their close relation to the thyroid gland, great care must be taken to avoid damage to them during thyroid surgery.

Quick Anatomy

Key Facts


Developmental precursor

Arterial supply

Venous drainage

Nervous supply

Lymphatic drainage

Neural crest cells and primitive pharynx.

Superior thyroid artery, a branch of the external carotid. Inferior thyroid artery, a branch of the thyrocervical trunk.

The superior and middle thyroid veins drain into the internal jugular vein. The inferior thyroid vein drains into the brachiocephalic vein.

Superior, middle and inferior cervical sympathetic ganglia.

Mainly deep cervical nodes. Some into paratracheal nodes.



The thyroid has two lobes connected by an isthmus and consists of follicles which produce thyroid hormones. During development the thyroid gland migrates from the floor of the pharynx to its adult location. Cysts and fistulas can remain along this developmental tract. Care is taken during thyroid surgery to avoid damage to the recurrent laryngeal nerves. Furthermore during tracheostomies and thyroid surgery caution must be taken to avoid the ima artery which is present in 10% of individuals, anterior to the thyroid gland.


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