An ovarian cyst is a fluid-filled sac(follicle) inside or on the surface of an ovary. If the fluid-filled sac grows larger than 2 cm, then it is considered an ovarian cyst.
An ovarian cyst can be anywhere from the size of a pea to the size of a grapefruit. Ovarian cysts affect women of all ages, although most often in women of childbearing years.
Most ovarian cysts are considered to be functional. Functional cysts form during the normal menstrual cycle. The sac(follicle) breaks open to release the egg and then dissolves.
When the sac(follicle) doesn't break, the fluid builds up inside and this in turn causes problems such as bleeding and pain. This is a non-functional cyst.
Ovarian Cysts No More