This MRCS Part B station tests your knowledge of the anatomy of the thyroid gland and surrounding structures.

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What is this?

Anatomy image for MRCS Part B

This is the thyroid gland.

The thyroid gland is located below the thyroid cartilage with the thyroid isthmus below the cricoid cartilage, invested in pretracheal fascia. It is attached to the 2nd to 4th tracheal rings by Berry's ligament, hence why it moves up on swallowing.

During development, the thyroid gland descends from the foramen caecum (2/3rds along the length of the tongue from the tip) to pass forward and loop around beneath the hyoid bone. Incomplete descent, therefore can lead to a lingual or pyramidal thyroid gland. An enlarged thyroid may expand downwards, resulting in a retrosternal thyroid.

Incomplete closure of the pathway of descent may also result in a thyroglossal duct cyst, which can become infected. During removal, the middle 1/3rd of the hyoid bone should also be excised to prevent recurrence.

A thyroglossal cyst is a differential for a midline neck mass. It will rise up on protrusion of the tongue on examination.