Ovarian cysts are sacs containing fluid or semisolid material that develop in or on the surface of an ovary. Most are harmless, but because they cause some of the same symptoms as ovarian tumors that may be cancerous, ovarian cysts should always be checked out.

The most common types of ovarian cysts are follicular cysts and corpus luteum cysts, which are related to the menstrual cycle. Follicular cysts occur when the cyst-like follicle on the ovary in which the egg develops does not burst and release the egg. These cysts are usually small and harmless, disappearing within two to three menstrual cycles. Corpus luteum cysts occur when the corpus luteum--a small, yellow body that secretes hormones--doesn't dissolve after the egg is released. They usually disappear in a few weeks but can grow to more than 4 in (10 cm) in diameter and may twist the ovary.

Ovarian cysts...