When thinking about cysts, which are simply collections of fluid, it is important to remember the normal function of the ovaries. During our reproductive years, our ovaries normally produce an egg every month. Each egg develops inside a small sac of fluid called a follicle. The follicle grows in the first 2 weeks of the menstrual cycle (during and after the period) and then the sac ruptures and the egg is released. After the egg is released the sac becomes what is called a “corpus luteum” and can continue to be visible as a fluid collection, often containing some blood from when the follicle ruptured.
If we were to do an ultrasound on a menstruating woman around 2 weeks after her period started (around the time of ovulation) it would be normal and expected to see a cyst measuring up to 2-3 cm in size on one ovary or the other. After ovulation we may see a similar sized cyst that appears blood filled. These type of cysts are called “functional” cysts, as they are related to the normal function of the ovaries. Generally they are not painful, and form and resolve monthly without consequence.
Occasionally functional cysts can be acutely painful, especially the corpus lutem variety which can hurt due to the irritation of blood inside the ovary. Rarely do these require surgery, and generally a short course of pain medication and waiting will allow them to resolve. If functional cysts become painful we often prescribe birth control pills, which prevent ovulation and generally will prevent functional cysts from forming. Another common type of blood filled cyst that causes pain in a premenopausal women is due to endometriosis. Endometrisois is a condition in which uterine lining cells (endometrial cells) grow outside the uterus, and bleed monthly as they are programmed to do, causing blood to build up in the affected area.
When endometriosis occurs inside the ovary, it can form a blood filled cyst which grows every month and does not resolve, becoming increasingly painful. These type of cysts do not resolve with pills, and often require surgery to remove. The most common reason to remove a benign cyst is pain. Sometimes cysts can grow very large and cause abdominal swelling or pressure and can sometimes twist or “torse” which is acutely painful as it cuts off the blood supply to the affected ovary.
A common diagnosis in premenopausal patients is Polycystic Ovarian Syndrome (PCO). This is a hormonal disorder which involves elevated testosterone and irregular ovulation. Rather than growing each month and releasing an egg, the follicles in PCO patients often stay small and undeveloped, and on ultrasound we many see a collection of tiny follicles (hence the name), none of which are getting the hormonal signal to grow and release and egg. The treatment for PCO focuses on treating the hormonal condition and does not require surgery on the ovaries themselves, since the ovarian cyts are a symptom of the underlying problem.
Ultrasound is good at differentiating what is inside the cyst, whether is is essentially just water (as in a follicular cyst), blood (as in a corpus luteum cyst or endometriosis) or solid material (as in other cysts). This can help us to understand if we are dealing with something other than a functional cyst. If a cyst appears solid in a premenopausal patient, the most likely diagnosis is a “dermoid cyst”, which is a benign cyst made up of various types of body tissue including teeth, hair, fat and skin. These cysts are not related to the cycle and do not resolve, and frequently grow large enough to cause pain, so they are generally surgically removed. While ovarian cancer is rare in premenopausal women, any solid ovarian mass is generally surgically removed to rule out this possibility.
Since postmenopausal women do not ovulate, they should not have functional cysts. Any cyst in a postmenopausal woman is suspicious for cancer and we will follow it very closely and surgically remove it if grows or looks suspicious. Cancer generally involves solid and cystic areas in combination (a “complex” cyst) and may be associated with an elevated level of CA125 in the blood. The CA125 test is not helpful in premenopausal women as it can be elevated for a variety of reasons, but an elevated CA125 along with a cyst in a postmenopausal woman warrants surgical removal.
If you have questions about ovarian cysts please let your provider know and we will help you to work through those questions.
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