Cysts may form within any tissue in the body. Cysts within the lung generally are air-filled, while cysts involving the lymph system or kidneys are fluid-filled. Migrating parasites -- such as trichinosis, dog tapeworm (Toxocara canis), and echinococcus -- form cysts within muscle, liver, brain tissue, the lungs, and the eye.

Cysts are common on the skin and develop as a result of infection, clogging of sebaceous glands, or around foreign bodies. They can also result from developmental abnormalities such as a pilonidal cyst (pilonidal dimple).