Ovarian cysts are fluid-filled sacs in or on an ovary. Women normally have two ovaries. They are the female organs that hold and release eggs. They also produce the female hormones estrogen and progesterone.
Functional cysts develop as a part of the normal functions of an ovary.
Usually they are smaller than abnormal cysts and they go away without treatment. A follicular cyst forms when the egg-producing follicle of the ovary gets bigger and fills with fluid. A corpus luteum cyst occurs after an egg has been released from the follicle. If pregnancy does not occur, the corpus luteum usually disintegrates. However, occasionally it swells with fluid or blood and remains on the surface of the ovary as a cyst.