What is a cyst?
A cyst is a closed capsule or sac-like structure, usually filled with liquid, semisolid, or gaseous material. Cysts usually occur within almost any type of the body's tissue; they vary in size from microscopic to large structures that can displace internal organs. Although cysts can also refer to any normal bag or sac formation in the body, in this article, we will use the definition stated above and consider it to be an abnormal formation. Consequently, the cysts discussed below are not normal parts of the body. They have distinct membranes or cyst walls. If the sac is filled with pus, it is usually considered an abscess, not a cyst.