AssessmentsThyroglossal duct cyst
Content Reviewers:Rishi Desai, MD, MPH
A thyroglossal duct cyst, sometimes just called a thyroglossal cyst, is a congenital disorder where the thyroglossal duct, which is a tiny canal connecting the thyroid gland with the tongue during fetal development, grows in size and fills up with mucus, which forms a cyst.
Now, normally during fetal development, a tiny depression, called the foramen cecum, forms at a spot between the front two-thirds and the back one-third of the tongue.
The tissue underlying the foramen cecum is different than the rest of the tongue, and it’s cells develop into the thyroid gland.
Through development, the thyroid gland tissue migrates downward as it grows, but it still stays connected by a tiny canal called the thyroglossal duct.
The thyroid gland descends down past the base of the tongue and the hyoid bone, which is a small bone present below the chin, before finally settles down in front of the trachea, in the neck.
The walls of the thyroglossal duct are lined by lymphoid cells, as well as epithelial cells which secrete mucus into the cavity.
Normally, once the thyroid gland has reached its final resting position, it stretches out a bit and the walls of the thyroglossal duct stick to each other, obliterating the canal.
Over time the thyroglossal duct starts to disintegrate and by the third month of fetal development, the duct is usually gone.
In some people, though, the thyroglossal duct doesn’t close completely, and instead parts of it widen to form pockets, or cysts.
The cysts get filled with mucus secreted by the epithelial cells in its walls.
These mucus filled thyroglossal duct cysts stick around as the fetus develops, and then they can cause a few problems.
For example, when there’s an infection of the respiratory tract, it can easily spread to the thyroglossal duct cyst since there are lymphoid, aka immune cells in the walls of the cyst.
Local inflammation also stimulates the epithelial cells of the thyroglossal duct cyst to increase their secretions, and that makes the cyst grow in size.
Second, the thyroglossal duct cysts can enlarge to a point where it bursts open, letting the mucus pour out and that can form a discharging sinus, which is sometimes also referred to as a thyroglossal fistula, even though it’s usually not a true fistula.