AssessmentsAnatomy of the thyroid and parathyroid glands
The superior cervical ganglia are indicated in the image below.
Content Reviewers:Viviana Popa, MD, Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.), Ghassan Tranesh, MD, MSC FCAP
The cervical viscera are composed of three layers named after their primary function.
The most superficial layer is the endocrine layer which contains the thyroid and parathyroid glands, then there’s the respiratory layer which contains the larynx and trachea and finally, the deepest layer is the alimentary layer which contains the pharynx and esophagus.
Let’s focus on the endocrine layer.
These lobes are united over the trachea by a thin isthmus, usually anterior to the second and third tracheal rings, giving it an H-shaped appearance.
In some people, there is a third lobe called the pyramidal lobe which usually arises from the isthmus and extends up to the hyoid bone.
Now, the thyroid gland is surrounded by a thin fibrous capsule which sends septa deeply into the gland, and this capsule is attached to the cricoid cartilage and the superior tracheal rings by dense connective tissue.
External to the capsule, the visceral portion of the pretracheal layer of deep cervical fascia forms a loose sheath, and between this loose sheath and the fibrous capsule, there’s the superior and inferior thyroid arteries which supply the gland.
The superior thyroid arteries are usually the first branches of the external carotid arteries and they descend to the superior poles of the gland, then pierce the pretracheal layer of deep cervical fascia and finally divide into anterior and posterior branches which supply mainly the anterosuperior aspect of the gland.
The inferior thyroid arteries are the largest branches of the thyrocervical trunks and they run superomedially posterior to the carotid sheaths to reach the posterior aspect of the gland where they divide into several branches that pierce the pretracheal layer of deep cervical fascia and supply the posteroinferior aspect of the gland, including the inferior poles of the gland.
In approximately 10% of people, there’s an additional small artery called thyroid ima artery which can arise from different locations such as the brachiocephalic trunk, the arch of aorta, the right common carotid artery, subclavian artery or internal thoracic artery.
The venous drainage of the thyroid gland is through three pairs of thyroid veins: superior thyroid veins which accompany the superior thyroid arteries and drain the superior poles of the gland, middle thyroid veins which run parallel with the inferior thyroid arteries and drain the middle of the lobes, and the inferior thyroid veins which drain the inferior poles of the gland.
That’s easy to remember, right?