Normal hormonal changes and ovarian cysts
Hormonal changes cause a type of ovarian cysts called physiologic cysts. These cysts can develop even in a female fetus -- as early as 12 weeks' gestation -- due to the hormonal changes in the pregnant woman's body. In most cases, physiologic cysts in the fetus disappear before birth. Those still present at birth generally disappear by age 3 months.
Ovarian cysts also occur frequently in adolescent girls. In adolescence, changes in the levels of hormones can have an unbalanced effect on the ovary that results in cyst formation. This type of hormonal imbalance usually resolves before age 18.
Two types of physiologic cysts can develop during a woman's menstrual cycle: One occurs before ovulation and one occurs after. In the first half of a woman's menstrual cycle, several follicles start to grow. One becomes the prime follicle, which typically continues to develop and release a mature egg. Sometimes this follicle remains a follicle and doesn't release an egg. The follicle can grow quite large and become a painful cyst.
The second type of physiologic cyst occurs after the egg develops and releases during ovulation. The remaining remnant of the follicle, now known as the corpus luteum, can develop into a corpus luteal cyst. These cysts can grow quite large and cause pain. If the released egg is not fertilized and therefore does not implant, hormone levels drop, which normally stops the growth of the corpus luteal cyst.
Other types of ovarian cysts
Non-physiologic cysts can also appear on the ovary: hemorrhagic cysts and endometriomas. A hemorrhagic cyst develops when the growth of an ovarian cyst ruptures a blood vessel, which bleeds into the cyst and causes pain. Hemorrhagic cysts sometimes require surgical removal, although many resolve on their own. Endometriomas are cysts caused by endometriosis, a growth of the tissue that lines the uterus in areas where it doesn't belong, such as on the ovary. Also known as "chocolate cysts" because they contain dark, bloody fluid, endometriomas can range in size and can cause pain. Your doctor may remove them if they interfere with fertility.
Dermoid cysts are unusual cysts; they are an example of “ovarian stem cells gone wild,” with all sorts of different cells, such as nerves, skin, teeth or hair growing in them. Dermoid cysts gave the first real evidence of the potential for stem cell research. Although dermoid cysts can often be left in place, many surgeons remove them, especially because on rare occasions they can become cancerous. Other doctors leave them in place unless they cause pain.