Corpus luteum cyst
This type of functional ovarian cyst occurs after an egg has been released from a follicle.
After this happens, the follicle becomes what is known as a corpus luteum.
If a pregnancy doesn't occur, the corpus luteum usually breaks down and disappears.
It may, however, fill with fluid or blood and persist on the ovary.
Usually, this cyst is found on only one side and produces no symptoms.