A branchial cyst, a.k.a. a branchial cleft cyst, is a small, fluid-filled sac that an look like a lump under the skin on the side of your neck, according to the Cleveland Clinic.

Branchial cleft malformations are usually small enough that they don’t have a significant health impact. However, if the mass is large enough, it may block your child's airways.

According to the Cleveland Clinic, it's unknown how common branchial cleft cysts (ones found on the side of the neck) are. "That's because not all branchial cleft cysts cause problems.

A thyroglossal duct cyst may appear similar to other growths around the neck, including: An epidermoid cyst, which is usually closer to the hyoid bone A branchial cleft cyst, which usually forms ...

Tennis legend Serena Williams says she recently underwent surgery to remove a branchial cyst “the size of a grapefruit” from her neck.

Branchial cleft cysts are sacs filled with fluid found in the neck and can appear as lumps or swelling under the skin. They can range from one centimeter to 10 centimeters (almost four inches) in ...

Williams added that the cyst was found in May and showed video of herself in a hospital bed. "They said I don’t need to get it removed if I don’t want," Williams wrote.

A branchial cyst, a.k.a. a branchial cleft cyst, is a small, fluid-filled sac that an look like a lump under the skin on the side of your neck, according to the Cleveland Clinic.

That said, branchial cleft cysts are one of the most common forms of neck masses or lumps, especially in children," the clinic's website notes.

The cyst can also become infected and form an abscess, or a painful, puss-filled pocket. Once branchial cysts begin growing, doctors will advise immediate removal to prevent further infection.