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. 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).

Johns Hopkins patient information

Last revised: December 3, 2012
by Martin A. Harms, M.D.

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