Persistent thyroglossal duct
| Persistent thyroglossal duct | |
|---|---|
 |
|
| Origin of Thyroglossal duct (Thyroid diverticulum) | |
| Classification and external resources | |
| Specialty | medical genetics |
| ICD-10 | Q89.2 |
| ICD-9-CM | 759.2 |
A persistent thyroglossal duct is a usually benign medical condition in which the thyroglossal duct, a structure usually only found during embryonic development, fails to atrophy. The duct persists as a midline structure forming an open connection between the back of the tongue and the thyroid gland.This opening can lead to fluid accumulation and infection, which necessitate the removal of the duct.
During the third week of development, the thyroid gland begins to develop from the floor of the pharynx. This primordium begins as an evagination between the first and second pharyngeal grooves, relatively where the anterior two-thirds of the tongue ends. This area is known as the foramen cecum and marks the origin of the thyroglossal duct. As the developing thyroid begins to travel to its intended destination, it remains connected to the tongue via the thyroglossal duct. By the seventh week of fetal development, the thyroid reaches its final position in the neck after growing through the mesoderm and musculature of the tongue, mouth, and neck. During the eighth to tenth week, the cells of the duct normally begin growing inwards and fill the previously hollow tube, beginning from the inferior end. This inferior end of the duct will then become the pyramidal lobe of the thyroid gland. The dividing cellular cords of the tubular duct become the isthmus and lateral lobes of the gland to complete the formation of the rest of the gland.
Once the thyroglossal duct involutes, the cells will begin to degenerate and disappear. However, in the case of a persistent thyroglossal duct, the tube remains hollow and continues to connect the foramen cecum to the thyroid gland.
The tongue develops after the thyroid primordium so the foramen cecum becomes buried at the base of the tongue. The thyroglossal duct then continues through the neck and lies anterior to the laryngeal cartilage. The duct then passes anteriorly to the developing hyoid bone; however, as the bone continues to grow it can continue to grow posteriorly, become anterior, or even grow to surround the duct. The duct is found very close to the medial line of the neck. The duct continues in front of the thyrohyoid membrane, sternothyroid muscle, and sternohyoid muscle, before terminating in the inferior segment of the neck at the thyroid.
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