What Is A Cyst? What Causes Cysts?

A cyst is a closed sac-like structure - an abnormal pocket of fluid, like a blister - that contains either liquid, gaseous, or semi-solid substances. A cyst is located within a tissue, and can occur anywhere in the body and can vary in size - some are so small they can only be viewed through a microscope, while others may become so big that they displace normal organs.