A
cyst is a closed sac, having a distinct
membrane and
division compared to the nearby
tissue. Hence, it is a cluster of cells that have grouped together to form a sac (not unlike the manner in which water molecules group together, forming a bubble); however, the distinguishing aspect of a cyst is that the cells forming the "shell" of such a sac are distinctly abnormal (in both appearance and behaviour) when compared to all surrounding cells for that given location. It may contain
air, fluids, or semi-solid material. A collection of
pus is called an
abscess, not a cyst. Once formed, a cyst may sometimes resolve on its own. When a cyst fails to resolve it may need to be removed by
surgery but this will depend on what type of cyst it is and where in the body it has formed.
