Thyroglossal duct cyst

by Jason Wasserman MD PhD FRCPC
September 9, 2024

A thyroglossal duct cyst is a fluid-filled pocket in the front of the neck, typically in the midline. It forms along the pathway that the thyroid gland follows during its early development. Normally, the thyroglossal duct disappears after the thyroid gland reaches its final position in the neck, but in some cases, part of the duct remains and can develop into a cyst. These cysts are benign (non-cancerous) and can occur at any age, although they are more common in children and young adults.

What are the symptoms of a thyroglossal duct cyst?

Symptoms of a thyroglossal duct cyst can vary, but common signs include:

• A painless lump in the front of the neck that may move when you swallow or stick out your tongue.
• Swelling or tenderness in the neck, especially if the cyst becomes infected.
• Difficulty swallowing or breathing in some cases if the cyst becomes large.

Occasionally, the cyst can become infected, leading to pain, redness, and fluid drainage from the cyst.

What causes a thyroglossal duct cyst?

A thyroglossal duct cyst forms when part of the thyroglossal duct (the pathway the thyroid gland follows during its development) does not entirely disappear. The remaining tissue can form a cyst, filling with fluid over time. Although the exact reason why some people develop these cysts is not fully understood, they are typically present from birth. They may enlarge or become noticeable later in life, often following an upper respiratory infection.

How is this diagnosis made?

The diagnosis of a thyroglossal duct cyst is typically made based on a physical exam and imaging studies. A doctor will examine the neck and may notice that the lump moves when you swallow or stick out your tongue. Imaging tests, such as an ultrasound or CT scan, can help confirm the diagnosis by showing the location and size of the cyst. Sometimes, a small sample of fluid from the cyst may be removed and examined to rule out other conditions. The diagnosis can also be made after the cyst is surgically removed and sent to a pathologist for examination under the microscope.

Microscopic features

When examined under a microscope, a thyroglossal duct cyst typically shows the following features:

• Cyst wall lined by epithelial cells: These cells can be of different types, such as columnar or squamous cells, similar to the cells lining other body parts like the skin or respiratory tract.
• Thyroid tissue in the cyst wall: Small amounts of thyroid tissue may be seen in the cyst’s wall, confirming that it developed from the thyroglossal duct.
• Inflammation: If the cyst has become infected or inflamed, there may be signs of inflammation, such as the presence of immune cells.

These features help pathologists confirm the diagnosis of a thyroglossal duct cyst.

What is the risk of developing cancer in a thyroglossal duct cyst?

While most thyroglossal duct cysts are benign, there is a small risk of developing cancer within the cyst. The most common type of cancer found in thyroglossal duct cysts is papillary thyroid carcinoma, a kind of thyroid cancer. However, this occurs in less than 1% of cases. If cancer is found, treatment typically involves surgery to remove the cyst and any remaining thyroid tissue, along with further treatment if necessary.