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What do cysts on the ovary mean?


I've been having some heavier bleeding and increased period cramps. I'm 34 and don't know why, but my doctor sent me for a pelvic ultrasound. He just called me saying the ultrasound showed a big cyst on my ovary. He wants me to see a gynecologist about it.
So I have two questions: What does a cyst on the ovary mean? And does having a cyst imply I must have surgery?


Thanks for your questions. I can best explain about ovarian cysts by reviewing with you the structure of the ovary and the process of ovulation or egg release.

The ovary is composed of a woman's lifetime store of hundreds of thousands of eggs plus supporting tissue, an outer coat and blood vessels that enter the centre of the ovary. Each of a woman's eggs has its own layer of encircling cells, sort of like a skin-this estrogen-making coat of cells together with the egg forms what we call a follicle.

Follicles move from the middle of the ovary toward the outer edge as they mature-this process continues regularly from birth until more than a year after our last period. As follicles mature they make more estrogen, get bigger and develop a lake of fluid in the middle. This fluid filled sac is called a cyst.

A follicle that has grown and matured so that it is ready to ovulate and release its egg has grown to be about 18 mm or half an inch across. With ovulation, that fluid-filled cyst bursts open. The fluid, egg and sometimes some blood are spilled into the abdomen. That can give a one-sided sharp pelvic pain called "Mittelschmertz" (in German, meaning "middle-pain") because it usually occurs about the middle of the menstrual cycle.

However, every month from the time we are babies, some dozen or more follicles start to grow. Some of these even develop enough to form cysts, but usually only one or none matures enough to ovulate. These smaller follicles with their lakes of fluid are called follicle cysts. These cysts are commonly the size of a pea. They are gradually absorbed by the ovary and disappear. These follicle cysts are common, perfectly normal, and occur in our ovaries long before we have our first period, when we are pregnant or on The Pill, and even occasionally after menopause. As we mature before our first period, our ovaries become stimulated and get larger, cysts are common, and occasionally cysts grow large enough to cause the ovary to twist and lose its blood supply (1). These follicular cysts are normal, don't need surgery and should be easy to see on pelvic or vaginal ultrasound as thin-walled fluid-filled circles around outer edge of the ovary.

Other follicles grow, make lots of estrogen and may develop into cysts that can become as large as a soft ball. These large follicles would have ovulated except for some imbalance in the complex system that stimulates ovulation. These cysts may remain in the ovary longer than follicular cysts, continue to grow, and occasionally cause discomfort by pressing on the bowels or bladder. These are anovulatory cysts and arise because of not ovulating. These large cysts are also fairly common, eventually are absorbed by the ovary and don't need surgery.

In some women, however, the hypothalamus and the pituitary have stimulated the ovary's outer coat to get thicker than its normal few cell layers. This outer coat, (called theca externa), makes estrogen and androgens (hormones such as testosterone that are normally high in men). The higher local and whole body levels of estrogen and testosterone interfere with ovulation. Thus anovulation (not ovulating) becomes chronic and often the ovary is ringed with multiple larger and thicker walled cysts. These cysts can make both estrogens and androgens-they are called "functional cysts." The person who has chronic anovulation with increased unwanted face or body hair, and a history of absent or rare periods has what CeMCOR calls Anovulatory Androgen Excess. This is also commonly called Polycystic Ovary Syndrome or PCOS. Either name means that for inherited and other reasons your body is not ovulating regularly, and is making too much estrogen and too much androgen-these changes cause far apart periods, unwanted male pattern hair and are also associated with weight gain especially around the waist, with an increased risk for diabetes. (Note: if you have been diagnosed with PCOS, you may qualify for a new study CeMCOR is just starting).

Occasionally following ovulation a cyst will form. After release of the egg, the part of the follicle left in the ovary, called the corpus luteum, that is now making progesterone as well as estrogen, may close off and fill with fluid. That is called a corpus luteum cyst. It is also not a worry because it is perfectly normal. The corpus luteum cyst should look different on ultrasound than other cysts.

Now to answer your second question-what to do? I suspect that you were not ovulating which caused your heavier flow and increased cramps. You may have a large cyst because of that. If it is a functional or follicular cyst it will be absorbed over several months. From what you said, that large cyst is not causing any discomfort and is unlikely to be pressing on the bladder, bowel or ureter-therefore it does not need surgery. To reassure yourself and your doctor, I'd suggest a repeat ultrasound in three months.

However, and this is important-you need to make sure your ultrasound report shows nothing suspicious of cancer like a solid bit or some non-liquid stuff inside the cyst. Note, also, that the ultrasound can't reliably tell the difference between ovarian cancer and rare but non-cancerous causes of cysts (cysts that grow teeth and hair called dermoids, or cysts filled with gummy stuff called cystadenomas). Because ovarian cancer is a very serious problem and hard to detect early (2), these suspicious-looking cysts need to be removed immediately.

I want to reassure you about ovarian cancer. Ovarian cancer is rare-only about 0.2% likelihood in our lifetimes. And most cysts are not cancer. Therefore even if the cyst on ultrasound looks suspicious, the likelihood of ovarian cancer is low. Also I want you to know that if you need to have surgery, and that one ovary with the cyst needs to be removed, your remaining ovary will do just fine. That's why we have two! One ovary is able to produce all the ovulations you need for your desired fertility and continued menstrual cycles until a usual age at menopause.

Hope this is helpful for you.

All the best,

Jerilynn C. Prior, MD, FRCPC


Reference List

  1. Merrill JA. The morphology of prepubertal ovary: relationship to the polycystic ovary syndrome. S.Med.J. 1963;56:225-31.
  2. Fung MF, Bryson P, Johnston M, Chambers A. Screening postmenopausal women for ovarian cancer: a systematic review. J Obstet Gynaecol.Can 2004;26(8):717-28.


Updated Date: 
Tuesday, November 19, 2013 - 12:00

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