A cyst is usually a fluid-filled sac, like a small water balloon. Cysts are almost always harmless, and many go away on their own. Usually they grow slowly. They can vary in size from as small as a pea to larger than a grapefruit. Many cause no symptoms at all. Often they are felt only during a pelvic exam. Ovarian cysts are usually not cancerous.
A functional cyst is the most common kind of cyst. It forms when a follicle does not release a mature egg or continues to grow after releasing the egg. Functional cysts usually occur on only 1 ovary at a time, and shrink on their own in 1 to 3 months. Rarely, a cyst will rupture, causing pain. Pain might also be caused by the twisting of an ovary that is enlarged because of the cyst growing on it.
Sometimes an unfertilized egg will start to grow into different kinds of tissue, such as skin, fat, hair, and teeth. This kind of cyst is called a dermoid cyst. Dermoid cysts can grow on 1 or both ovaries. Usually they cause no symptoms. But if they leak or the ovary becomes twisted, they can cause severe pain.
Endometrioma ("chocolate" cyst)
Sometimes tissue similar to the lining of the uterus (endometrium) grows and becomes part of the ovary. This kind of cyst is often called a “chocolate” cyst because of its dark-brown color. These cysts can grow on 1 or both ovaries. They often cause pain, especially around menstruation or during sexual intercourse.
If the capsule that surrounds the ovary grows, it can form a cystadenoma. These cysts can grow on 1 or both ovaries. Usually they cause no symptoms if they are small. But if they become large, they can press on organs near the ovaries, causing pain. They can also cause pain by stretching the ovarian capsule. A cyst that pushes on the bladder can cause frequent urination. Sometimes these cysts rupture and bleed.
These cysts can invade other tissues or spread to other parts of the body.