There are several different kinds of ovarian cysts, 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 cysts are the most commonly seen type of ovarian cyst. The ovaries are two small, round organs in the female reproductive system that release an egg every month. Each egg is formed in a tiny structure inside the ovary called a follicle. Sometimes, a follicle does not release an egg or does not shed its fluid. If this happens, the follicle can get bigger as it swells with fluid. This becomes a follicular ovarian cyst. It normally goes away without treatment after a few weeks.
Luteal cysts are less common. They develop when the tissue that is left behind after an egg has been released (the corpus luteum) fills with blood. Luteal cysts usually go away on their own within a few months, but can sometimes rupture (split), causing internal bleeding and sudden pain.
Dermoid cysts are the most common type of pathological cysts. They develop from an egg within the ovary and can contain a range of tissues, such as hair, skin or teeth. Dermoid cysts can grow to a large size and there is a risk remaining healthy ovarian tissue will be damaged, they are therefore best removed surgically.
Cystadenomas develop from cells that cover the outer part of the ovary. Some are filled with a watery liquid and others with a thicker, mucous substance.
Cystadenomas are often attached to an ovary by a stalk rather than growing inside the ovary itself, which means they can grow to a large size. They are not normally cancerous, but need to be surgically removed to allow a thorough histology (microscope) assessment.
Endometriomas are blood-filled cysts on the ovary. They can cause pain, in particular painful periods and pain with intercourse (dyspareunia). Laparoscopy and removal of the cyst is often necessary.