There are several common causes of ovarian cysts. The first is during the ovulation process where the follicle fails to release an egg, resulting in the formation of follicular cysts. The ultrasound typically shows these as simple cysts containing follicular fluid. Another situation is the corpus luteum cyst, which occurs after ovulation when the ovary forms a wound surface and a corpus luteum. Cysts can also develop during the growth of the corpus luteum. These two types of cysts generally disappear after the next menstrual period and are considered physiological cysts that usually require no treatment. However, some cysts result from pathological changes in ovarian cells, or even from tumors. On an ultrasound, these appear differently, often as mixed composition masses, in which case surgical treatment is recommended.