Ovarian cysts often develop naturally in women who have monthly periods.
They can also affect women who have been through the menopause.
Types of ovarian cyst
There are many different types of ovarian cyst, which can be categorised as either:
- functional cysts
- pathological cysts
Functional ovarian cysts are linked to the menstrual cycle. They affect girls and women who haven't been through the menopause, and are very common.
Each month, a woman's ovaries release an egg, which travels down the fallopian tubes into the womb (uterus), where it can be fertilised by a man's sperm.
Each egg forms inside the ovary in a structure known as a follicle. The follicle contains fluid that protects the egg as it grows and it bursts when the egg is released.
However, sometimes a follicle doesn't release an egg, or it doesn't discharge its fluid and shrink after the egg is released. If this happens, the follicle can swell and become a cyst.
Functional cysts are non-cancerous (benign) and are usually harmless, although they can sometimes cause symptoms such as pelvic pain. Most will disappear in a few months without needing any treatment.
Pathological cysts are cysts caused by abnormal cell growth and aren't related to the menstrual cycle. They can develop before and after the menopause.
Pathological cysts develop from either the cells used to create eggs or the cells that cover the outer part of the ovary.
They can sometimes burst or grow very large and block the blood supply to the ovaries.
Pathological cysts are usually non-cancerous, but a small number are cancerous (malignant) and often surgically removed.
Conditions that cause ovarian cysts
In some cases, ovarian cysts are caused by an underlying condition such as endometriosis.
Endometriosis occurs when pieces of the tissue that line the womb (endometrium) are found outside the womb in the fallopian tubes, ovaries, bladder, bowel, vagina or rectum. Blood-filled cysts can sometimes form in this tissue.
Polycystic ovary syndrome (PCOS) is a condition that causes lots of small, harmless cysts to develop on your ovaries. The cysts are small egg follicles that don't grow to ovulation and are the result of altered hormone levels.