A follicular cyst is a type of ovarian cyst. Usually benign, it develops if an ovary does not release a mature egg. The follicle, which is a sac that holds the egg until it is mature enough to be released, typically disintegrates and disappears after the release of the egg. Sometimes, a malfunction in the process results in a persistent, fluid-filled sac called a follicular cyst.
When the ovulation process happens properly, an egg is released from the ovary at the middle point of the reproductive cycle, triggered by a burst of luteinizing hormone (LH). There are times when the LH burst doesn't happen, however, and no signal is given. This results in ovulation not occurring or a mature follicle collapsing instead of being released.
When this happens, the unreleased egg grows into a cyst, and is still attracted to the ovary walls by the follicle. These fluid-filled sacs can reach up to 2 inches (5.08 cm) in diameter, eventually rupturing and, occasionally, causing a sharp pain in the middle of the menstruation cycle. Often, there is no sharp pain, however, and no symptoms to go with the development and bursting of the cyst.
The sharp pain associated with the rupturing of follicular cysts is called mittelschmerz, a German word that means middle pain. It has a number of causes, and in the case of these cysts, it is typically felt about two weeks before menstruation begins, or in the middle of the cycle. The cysts typically happen in only one ovary at a time, and the pain is felt on that side of the body.
Follicular cysts belong to a group of what is called functional cysts. This refers to the fact that they are caused by a misfire in the normal function of the menstruation cycle. Also a part of this family are corpus luteum cysts, which occur when the follicle does not disintegrate as it should.
For the most part, these cysts are harmless and disappear on their own. Approximately a quarter of all woman experience follicular cysts, and as they often have no symptoms accompanying them, the individual is usually unaware of their existence. Cysts such as these are considered a normal part of the function of the reproductive system, and are often referred to as physiologic. While there is no way to prevent these cysts from happening, changes in the menstruation cycle, including sharp pains and irregularities, should be checked with a doctor.