What is the embryology and anatomy of the thyroid gland relative to thyroidectomy?

Updated: May 08, 2018
  • Author: Neerav Goyal, MD, MPH; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

The thyroid gland starts developing on approximately the 24th day of gestation from endodermal epithelial cells on the median surface of the pharyngeal floor—the foramen cecum. It develops caudal to the median tongue bud, which arises from the first pharyngeal arch, and rostral to the copula, which develops from the second pharyngeal pouch. By the seventh gestational week, the thyroid gland descends anterior to the hyoid bone, thyroid cartilage, and cricoids cartilage to rest anterior to the trachea. The path of descent is marked by the thyroglossal duct, a tubular structure of thyroid tissue, that usually obliterates completely between the 7th and 10th gestational week. However, a persistence of the inferior-most aspect of this duct is present in as many as 50% of patients in the form of the pyramidal lobe. [8, 9]

Thyroid embryology. Thyroid embryology.

The fully developed thyroid gland is composed of 2 lateral lobes and a central isthmus with or without a pyramidal lobe (40-50%). The thyroid lies in the middle layer of the deep cervical fascia and is attached from its superior-medial aspect to the thyroid and cricoid cartilages via the anterior suspensory ligament. Berry’s ligament (the posterior suspensory ligament) connects the posterior-medial aspect to the first and second tracheal ring and the cricoid cartilage. The sternohyoid and sternothyroid muscles cover the thyroid gland anteriorly. The tubercle of Zuckerkandl extends off of the posterior and lateral aspect of the thyroid lobes. [8, 9]

The thyroid gland is a very vascular structure. The major arterial contributions are the superior thyroid artery, a branch off of the external carotid artery, and the inferior thyroid artery, which branches off of the thyrocervical trunk. Lastly, the thyroidea ima artery can provide an arterial supply through the inferior border of the isthmus in 2-12% of patients. [10] It branches from either the innominate, subclavian, right common carotid, internal mammary, or the aortic arch.

Thyroid anatomy. Thyroid anatomy.

The superior, middle, and inferior thyroid veins provide venous drainage and join either the internal jugular or innominate veins. The superior thyroid vein follows the pathway of the superior thyroid artery. The middle thyroid veins directly flow into the internal jugular vein. The inferior thyroid veins can be found just anterior to the trachea and often anastomose with each other. Lymphatic drainage tends to follow venous drainage and leads to the prelaryngeal, pretracheal, paratracheal, and supraclavicular nodes. The gland is innervated by the superior, middle, and inferior cervical ganglia of the sympathetic trunk, as well as by parasympathetic fibers from the vagus nerve. [8, 9]


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