A cyst is usually a fluid-filled sac, like a small water balloon. These cysts are almost always harmless, and many go away on their own. No one knows exactly why cysts form. Usually they grow slowly, and they are rarely cancerous in women under 50. 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.
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 one ovary, and shrink on their own in 1 to 3 months. Rarely, a cyst will twist or rupture, causing pain.
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 one or both ovaries. Usually they cause no symptoms. But if they leak or become twisted, they can cause severe pain.
Endometrioma ("Chocolate" Cyst)
Sometimes tissue similar to the lining of the uterus (endometrium) grows and attaches to the outside of the ovary. This kind of cyst is often called a "chocolate" cyst because of its dark-brown color. These cysts can grow on one 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 one or both ovaries. Usually they cause no symptoms. But if they become large, they can press on organs near the ovaries, causing pain. A cyst that pushes on the bladder can cause frequent urination. Sometimes these cysts rupture and bleed.