Branchial cleft cyst

by Jason Wasserman MD PhD FRCPC
September 11, 2024

A branchial cleft cyst is a fluid-filled sac that forms on the side of the neck, usually just in front of the ear or under the jaw. It develops from tissues in the neck that didn’t fully form during embryonic development. These cysts are typically benign (non-cancerous) and can appear at any age, though they are often noticed in children or young adults.

What are the symptoms of a branchial cleft cyst?

The symptoms of a branchial cleft cyst may vary, but common signs include:

• A soft, painless lump on the side of the neck or just below the ear.
• Swelling in the neck, which may increase in size over time or after an upper respiratory infection.
• Tenderness or discomfort, especially if the cyst becomes infected.
• Drainage of fluid from the cyst if it opens up to the skin.

What causes a branchial cleft cyst?

A branchial cleft cyst forms when parts of the tissue in the neck that develop during early life do not disappear as they normally would. These leftover tissues can form a cyst over time. While the exact reason why this occurs is not fully understood, it is thought to be related to how the neck and throat form during the early stages of fetal development.

How does a branchial cleft cyst develop?

During embryonic development, structures in the neck called branchial clefts normally disappear as the tissues in the neck and throat form. If these clefts don’t close properly, they can leave behind small spaces that may eventually fill with fluid, creating a cyst. These cysts can remain small and unnoticed or grow larger over time, especially if they become infected.

How is this diagnosis made?

The diagnosis of a branchial cleft cyst is typically made based on a physical exam and imaging studies. Doctors can often identify the cyst by its location and appearance. Ultrasound, CT scan, or MRI may be used to confirm the diagnosis and check the size and position of the cyst. In some cases, a sample of fluid from the cyst may be examined to rule out other conditions.

Does a branchial cleft cyst need to be removed?

In most cases, a branchial cleft cyst is surgically removed. While the cyst itself is not harmful, it can become infected, leading to swelling, pain, and drainage. Removing the cyst also helps prevent recurrence or complications. Surgery is usually a simple procedure and is the most effective way to ensure the cyst does not return.

What are the microscopic features of a branchial cleft cyst?

Under the microscope, a branchial cleft cyst typically shows the following features:

• Cyst wall lined by epithelial cells: These epithelial cells can be either squamous (similar to skin cells) or respiratory-type epithelium (similar to the lining of the respiratory tract).
• Lymphoid tissue resembling lymph nodes may also be present in the wall of the cyst.
• Chronic inflammation: If the cyst has become infected, signs of inflammation, including immune cells like lymphocytes and plasma cells, may be visible.

These features help pathologists confirm the diagnosis of a branchial cleft cyst.

Is there any risk of cancer in a branchial cleft cyst?

While the majority of branchial cleft cysts are benign and do not carry a significant risk of cancer, very rare cases of cancer (such as squamous cell carcinoma) have been reported to develop in these cysts. Because of this small risk, surgical removal of the cyst is often recommended to both eliminate the possibility of infection and address the rare chance of malignant transformation.