There are several different kinds of ovarian cyst, which are categorised as either:
- functional cysts (the most common type): harmless cysts that form as part of the menstrual cycle
- pathological cysts: tumours in the ovaries that are either benign (harmless) or malignant (cancerous)
There are two types of functional ovarian cyst:
- follicular cyst
- luteal cyst
These are described below.
Follicular cysts are the most commonly seen ovarian cysts.
The ovaries are two small, bean-shaped organs that are part of the female reproductive system. They release an egg every month which moves into the womb (uterus) where it is fertilised by a man's sperm.
Each egg forms in a tiny structure inside the ovary called a follicle. The follicle contains fluid to protect the egg as it grows and it bursts when the egg is released.
However, sometimes a follicle does not release an egg, or it does not shed its fluid and shrink after the egg is released. If this happens, the follicle can get bigger as it swells with fluid. The fluid-filled follicle becomes a follicular ovarian cyst.
Usually, only one cyst appears at a time and it will often disappear without treatment after a few weeks.
Luteal cysts are less common than follicular cysts. They develop when the tissue that is left behind after an egg has been released, known as the corpus luteum, fills with blood.
Luteal cysts usually disappear on their own within a few months, but they can sometimes rupture (burst), causing internal bleeding and sudden pain.
A dermoid cyst, is the most common type of pathological cyst in women who are under 40 years old.
In women over 40 years of age, a cystadenoma is the most common type.
Dermoid cysts develop from the cells that are used to create eggs. As eggs have the ability to create any type of cells, dermoid cysts can consist of a wide range of different types of human tissue, including blood, fat, bone and hair.
Dermoid cysts have the potential to grow very large. They can sometimes grow up to 15cm (6 inches) in diameter. They are not usually cancerous, but will usually need to be surgically removed.
Cystadenomas develop from cells that cover the outer part of the ovary. There are two main types of cystadenomas:
- serous cystadenomas
- mucinous cystadenomas
Serous cystadenomas do not usually grow very large but they can cause symptoms if they rupture.
In contrast, mucinous cystadenomas can grow very large (up to 30cm or 12 inches), filling up the inside of the abdomen and placing pressure on other organs, such as the bladder and bowel.
This can result in symptoms such as:
- a frequent need to urinate
Larger mucinous cystadenomas carry the risk of rupturing, or blocking the blood supply to the ovaries (torsion). As with dermoid cysts, mucinous cystadenomas are rarely cancerous.
Conditions that cause ovarian cysts
If you have endometriosis, you may develop ovarian cysts. Endometriosis occurs when pieces of the tissue that lines the womb (the endometrium) are found outside the womb in areas such as the fallopian tubes, ovaries, bladder, bowel, vagina or rectum. Sometimes, blood-filled cysts can form in this tissue.
See the Health A-Z topic about endometriosis for more information.
Polycystic ovarian syndrome
Polycystic ovarian syndrome is a condition that causes lots of small, harmless cysts to develop on your ovaries. The cysts develop if there is a problem with the balance of hormones that are produced by the ovaries.
See the Health A-Z topic about polycystic ovarian syndrome for more information.