Thyroglossal duct cyst

A 17-year-old girl presents to the physician for evaluation of a neck mass. She first noticed the mass five weeks ago, following an upper respiratory infection. She has not experienced any dyspnea or dysphagia. Past medical history is unremarkable. Temperature is 37.5°C (99.5°F), blood pressure is 109/72 mmHg, and pulse is 68/min. On physical examination, a midline mass is observed over the anterior neck around 1 centimeter below the hyoid bone. The mass is soft and nontender to palpation. The mass moves when the patient swallows. Which of the following best describes the underlying cause of this patient’s condition?

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.

Key Takeaways

A thyroglossal cyst is an irregular neck mass or a lump that had developed from cells and tissues left over after the formation of the thyroid gland during developmental stages. As the thyroid gland descends during development a tiny thyroglossal duct forms. If the thyroglossal duct doesn't close in on itself, it can start to fill up with mucus which creates cysts anywhere along its tract. These cysts are usually midline on the neck, just above or below the hyoid bone, and can be surgically removed.

The most common location for a thyroglossal duct cyst is in the midline of the neck, just below the hyoid bone. The cyst may be small or large and can be moveable or fixed. It may be painless or tender, and in some cases, it can become infected or cause difficulty swallowing or breathing if it grows large enough to press on nearby structures. The diagnosis of a thyroglossal duct cyst is usually done with an imaging study like an ultrasound or CT scan and confirmed with fine needle aspiration. Treatment involves surgical removal of the entire thyroglossal tract, which may be accompanied by antibiotics if an infection is present.

Sources

"Robbins Basic Pathology" Elsevier (2017)

"Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)

"Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)

"CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)

"Thyroglossal Duct Cyst—More Than Just an Embryological Remnant" Indian Journal of Surgery (2010)

"CERVICAL CYSTS AND FISTULAE OF THYROGLOSSAL TRACT ORIGIN" Annals of Surgery (1954)

Thyroglossal duct cyst

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