A cyst is a closed pocket or pouch of tissue. It can be filled with air, fluid, pus, or other material.
Cysts may form within any tissue in the body. Most cysts is the lungs are filled with air. Cysts that form in the lymph system or kidneys are fluid-filled. Certain parasites, such as trichinosis, dog tapeworm (Toxocara canis), and echinococcus, can form cysts within the muscles, liver, brain, lungs, and eyes.
Cysts are common on the skin. They can develop from a clogged sebaceous glands (acne-related cysts) or form around something stuck in the skin. These cysts are benign (not cancer) but can cause pain and changes in appearance.
Cysts can be drained or removed with surgery depending on the type and location of the growth.
A pilonidal dimple is a type of cyst.