Chocolate cysts are noncancerous, fluid-filled cysts that typically form deep within the ovaries. They get their name from their brown, tar-like appearance, looking something like melted chocolate. They’re also called ovarian endometriomas.

The color comes from old menstrual blood and tissue that fills the cavity of the cyst. A chocolate cyst can affect one or both ovaries, and may occur in multiples or singularly.

Chocolate cysts occur in of women who have endometriosis, estimates the Endometriosis Foundation of America. Endometriosis is a common disorder in which the lining of the uterus, known as the endometrium, grows outside the uterus and onto the ovaries, fallopian tubes, and other areas of the reproductive tract. The overgrowth of this lining causes severe pain and sometimes infertility.

Chocolate cysts are a subgroup of endometriosis. They’re with more severe forms of the disorder.

What are the symptoms?

Chocolate cysts may cause symptoms in some women. Other women may not experience any symptoms. The size of the cyst also doesn’t necessarily affect the severity or presence of symptoms. This means a woman with a small cyst may experience symptoms, while someone with a large one may not. Cysts can range from 2 to 20 centimeters (cm) in size.

When symptoms do occur, they’re similar to those of endometriosis. They can include:

If a chocolate cyst ruptures, it can cause severe, sudden abdominal pain on the side of the body where the cyst is located. A ruptured cyst can be a medical emergency. Seek immediate medical attention if you suspect you have a ruptured cyst.

What causes chocolate cysts?

There’s a lot of debate as to how and why chocolate cysts form. One theory is that they form via something called retrograde menstruation. It may be a result of endometriosis.

Each month, in response to fluctuating levels of the female hormones estrogen and progesterone, the uterine lining grows and then is shed for most women of reproductive age.

But in women with chocolate cysts, it’s thought that instead of some of this menstrual blood and tissue being expelled out the vagina, it adheres to one or both ovaries. It then eventually infiltrates the organ and implants within the ovaries, causing cysts.

The lining of these cysts acts much the way the lining of the uterus does. It grows and is then shed in response to the monthly rise and fall of female hormones. But instead of leaving the body, this tissue becomes trapped within the cavity of the cyst. Here it can produce inflammation and disrupt the ovaries.

How are chocolate cysts diagnosed?

Your doctor may order a pelvic ultrasound if:

  • they feel a cyst during a pelvic exam
  • they suspect you have endometriosis based on your symptoms
  • you’re experiencing unexplained infertility

An ultrasound can identify if a cyst is present. But it can’t necessarily determine what type of cyst it is.

To definitively diagnose a chocolate cyst, your doctor will extract fluid and debris from inside the cyst. This is usually done with a needle biopsy.

During a needle biopsy, your doctor will use ultrasound to help them insert a needle through the vagina into the ovarian cyst. The extracted fluid is then examined under a microscope. Your doctor can diagnose the type of cyst using the results from the needle biopsy.

How are chocolate cysts treated?

Treatment will depend on several factors, including:

  • your age
  • your symptoms
  • whether one or both ovaries are affected
  • whether or not you want to have children

If the cyst is small and not producing symptoms, your doctor may advise a watch-and-wait approach. They may also recommend medication that inhibits ovulation, such as the birth control pill. This can help control pain and slow the growth of cysts, but it can’t cure them.

Surgery to remove the cysts, called an ovarian cystectomy, is often recommended for women who have:

  • painful symptoms
  • cysts larger than 4 cm
  • cysts that may be cancerous (but a 2006 review estimates less than of cysts are cancerous)
  • infertility

The surgery is generally done via a laparoscope. A laparoscope is a thin, long tube with a light and camera on the end that help doctors perform the procedure. It’s inserted through a small incision.

The surgery is controversial in terms of whether it hurts or helps fertility. Even when the surgeon is highly skilled, healthy ovarian tissue can be removed along with the cyst. That may negatively affect ovarian function. However, the inflammation and toxic environment a chocolate cyst can produce may do more harm to fertility than surgery.

Discuss all of your options and concerns with your doctor before beginning treatment.

What effect do chocolate cysts have on fertility?

Chocolate cysts can invade, damage, and take over healthy ovarian tissue. This can be a serious threat to fertility. These cysts can be difficult to treat, and the pelvic surgeries used to control or remove them can lead to ovarian scarring and reduced fertility.

When compared to women without chocolate cysts, women with them also :

  • fewer eggs
  • eggs that are less likely to mature
  • higher levels of follicle-stimulating hormone (FSH), which can indicate problems with the ovaries

Despite the damage chocolate cysts do to ovaries, many women with them can conceive naturally. A followed women with regular menstrual cycles and chocolate cysts on only one ovary. Researchers found 43 percent of them were able to become pregnant naturally. The women were followed for four years.

In vitro fertilization (IVF) is another option if you have chocolate cysts and difficulty becoming pregnant. that women with these cysts have similar pregnancy, implantation, and delivery rates with IVF as women with tubal factor infertility.

What’s the outlook?

Chocolate cysts are common in women with endometriosis. Symptoms can often be managed with medication. In some cases, the cysts will need to be removed.

According to a 2006 study, about of surgically removed chocolate cysts will return, especially if they were large or medically treated. Getting pregnant after surgery may lower the risk of recurrence.

Talk to your doctor about your treatment options. Let them know if you’re planning or considering having children in the future. This will help them develop an appropriate treatment plan for you.