Serena Williams just had a cyst “the size of a small grapefruit” removed from her neck. That’s what it means

Tennis star Serena Williams shared in a TikTok posted Tuesday that she had a cyst removed from her neck, one the size of a “small grapefruit.”

“One day in May, I found this big lump on my neck,” Williams says in the video. “I was mortified. I was tested, everything you can imagine, it was all negative.”

The mass was diagnosed as a benign branchial cyst. In the caption, Williams wrote that her doctors said she didn’t have to take it out, “but it kept growing.” When she got older, her doctors advised her to have it removed as soon as possible, as it could leak or get infected. infected

Here’s what you need to know about the type of cyst Williams had.

What are cysts?

The most common types of cysts are epidermoid cysts, which form under the skin and are small, harmless bumps that are most often found on the face, neck, or trunk, according to the Mayo Clinic. Epidermoid cysts are caused either by cells moving deeper into the skin instead of shedding, or by irritation or injury to the skin or a hair follicle.

They are often slow-growing and painless, rarely causing problems or needing treatment; however, cysts are removed when they are bothersome, open or become painful, or become infected.

What is a benign branchial cyst?

The type of cyst that Williams had is different from the everyday cysts that people usually encounter. A branchial cyst, according to the Cleveland Clinic, is a small fluid-filled sac that can look like a lump under the skin on the side of the neck. It’s considered one of the most common cervical masses, and while Williams admitted she was “a little scared,” it’s largely harmless.

These cysts are considered congenital, meaning they are present at birth. Although children are more likely to be diagnosed with them, they can be noticed later in life if they are infected.

What causes a branchial cyst?

The Cleveland Clinic says that branchial cysts can form during fetal development, when the branchial arches, which are responsible for the development of certain parts of the head and neck, do not fuse or grow together. When gaps are left between the arches, certain branchial abnormalities such as branchial fissure cysts can develop.

How did it get so big?

Branchial cysts can grow if they become infected, usually from an upper respiratory infection like the common cold, according to the National Institutes of Health. The cyst can also become infected and form an abscess, or a painful pocket filled with pus.

Once branchial cysts begin to grow, doctors will advise immediate removal to prevent further infection. The cyst rarely comes back after removal, the Cleveland Clinic says, and surgery is likely to completely resolve the problem.

For Williams, even though the cyst was removed, she was exhausted by the process: In the same video explaining her surgery, she included a clip of herself taking her daughter to the American Girl Doll store, pointing out the bandage around the neck, saying that she “Needed to keep showing up.”

Williams adds, “I’m going to go home and pass out.”

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This story was originally featured on Fortune.com