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This is a type of cyst caused by endometriosis on the ovary. They are often known as “chocolate cysts” because they contain brown liquid inside of them that resembles chocolate syrup.

It’s typically never “just an endometrioma”.

Multiple studies have shown that ovarian endometriomas are often an indication that the person also has more severe pelvic and intestinal endometriosis. If your doctor says that you “just have an endometrioma”, you may want to seek a second opinion with an expert excision surgeon. This way you get all of your endometriosis excised at once, without endometriosis being missed or you needing to reoperate for it.

Surgical treatment of endometriomas.

Medical treatment (Lupron, Orilissa, birth control) doesn’t resolve endometriomas, so surgical treatment is typically necessary.

Sometimes it can appear that an endometrioma is “shrinking” when follow up ultrasounds are done. However, this reduction in size is likely due to a change in density of the endometrioma components or a slow leakage of the chocolate fluid out of the endometrioma into the pelvis.

When a person is taking hormonal suppression, there may also be a temporary reduction in size due to decreased inflammation, but once a person goes off the medication, the endometrioma often increases in size again. However, as mentioned above, endometriomas don’t resolve with medical treatment.

Various studies have shown that endometriomas are rarely found by themselves. Typically a person with an endometrioma has more areas of endometriosis, so an endometrioma having a slight decrease in volume doesn’t change the rest of your lesions or their severity. Depending on the size and the endometrioma itself, it can be stuck to the rectum, ureters, the uterus, the other ovary, etc. It can take an hour or more to remove the endometrioma, and then the rest of the surgery has to begin! For all of these reasons, endometriomas, like all endometriosis, is best treated by an expert excision surgeon.

What surgical technique to use?

There are various ways to surgically treat an endometrioma, including drainage, ablation, excision, and sclerotherapy (when the endometrioma is drained and a fluid is injected into the cyst, usually Ethanol. The fluid is usually kept in the cyst for 5-10 minutes, but occasionally it is not removed.)

Excision of an endometrioma is generally preferred. Both the 2022 European endometriosis guidelines as well as ACOG guidelines state that studies show that excision of an endometrioma has lower recurrence rates of endometriosis-associated pain and of the endometrioma itself compared to drainage and ablation of the cyst wall. However, surgery may lower AMH, damage the ovary, or reduce ovarian reserve, so it’s important to:

  • see an expert excision surgeon with the necessary skills to operate on an endometrioma.

“The level of expertise in endometriotic surgery is inversely correlated with inadvertent removal of healthy ovarian tissue along with the endometrioma capsule.” (1)

  • have a conversation with the surgeon about your treatment goals, even if fertility isn’t a concern.

When to operate?

Some doctors prefer to wait until endometriomas reach a certain size, such as 4 cm, before operating. Others will operate depending on a patient’s pain or fertility goals. 

“Endometriomas of 6 cm or more in diameter may be associated with increased risks for infection, rupture, and even malignancy, and therefore, surgical intervention is considered obligatory.” (1)

While surgery may lower AMH, damage the ovary, or reduce ovarian reserve, an untreated endometrioma may also do the same.

“Brosens et al. reported that…[endometriomas are] associated with inflammation independent of the lesion’s size, leading to fibrosis of the ovarian cortex, smooth muscle cells metaplasia, and loss of oocytes.” (1)

Speak to your qualified surgeon about your treatment goals, symptoms, and what/when treatment is right for your individual case.

Hormonal suppression

Endometriomas can be responsive to ovarian hormones, therefore some people taking a wait-and-see approach to their endometrioma may decide to go on hormonal suppression with the goal of suppressing ovarian activity to try and reduce pain and inflammation. I’m personally not familiar with any studies comparing endometrioma growth on and off hormonal suppression. Endometriomas may or may not progress in size with or without medical treatment. If one is taking a wait-and-see approach (whether they are on hormonal suppression or not), they can routinely monitor their endometriomas via ultrasound.

Endometriomas have a higher recurrence rate.

Endometriomas have a higher risk of recurrence than other types of endometriosis, even in the hands of an expert. And when they are not excised (and instead are drained and the cyst wall ablated), the rate of persistence (endometriosis remaining because it was never properly removed in the first place) is even higher.

However, it’s important to know that if your endometrioma recurs, this doesn’t mean that your endometriosis in other areas has also recurred.

Hormonal suppression and endometrioma recurrence.

Some studies done on endometriomas suggest that taking hormones post operatively can sometimes help to slow potential endometrioma recurrence for some people. (Important note: I’m speaking here about endometrioma recurrence, and not recurrence of superficial or deeply infiltrating endometriosis). 

Closer look at the study “Long-term adjuvant therapy for the prevention of postoperative endometrioma recurrence: a systematic review and meta-analysis”

A systematic review and meta-analysis by Vercellini et (2) al looked at 4 studies comparing use of oral contraceptives (OC) for at least 12 months post excision of an endometrioma vs. expectant management (no use of oral contraceptives). Patients were monitored for endometrioma recurrence via ultrasound (endometriomas of at least 1.5 cm in one study or 2 cm in 3 studies) and/or histological confirmation.

Across the 4 studies, there were a total of 965 patients enrolled (726 in three cohort studies and 239 in one randomized controlled trial.) 

They compared the endometrioma recurrence rates in patients who used oral contraceptives during the entire study follow-up period. These were “always” users. There were also “ever” users, which were patients who used oral contraceptives at some points but not during the entire time. “Never” users were patients who didn’t use oral contraceptives post excision during the study follow-up period.

Always vs never users: “A recurrent endometrioma was identified in 33 of 423 (8%) “always” OC users and in 117 of 341 (34%) women [“never” users] who underwent expectant management (pooled odds ratio 0.12; 95% confidence interval 0.05–0.29).”

Always vs ever users: “In order to determine whether duration of OC use had an effect on the study outcome, we considered the three cohort studies and compared the endometrioma recurrence rate observed in the 275 “always” users and in the 179 “ever” users. In the former group, 16 endometriotic cysts were detected (6%; 95% CI 4–9%), compared with 48 in the latter (27%; 95% CI 21–34%).”

This study found that “Postoperative OC use dramatically decreased the risk of ovarian endometrioma recurrence, especially in women who used OCs regularly and for prolonged periods.”

Discussion about this study

The study by Vercellini et al above looked specifically at oral contraceptives taken for at least 12 months post excision of an endometrioma. (In fact, the follow up periods in the 4 studies reviewed were 24-35 months.)

While the “always” and “ever” oral contraceptive users had an overall lower endometrioma recurrence rate than “never” users, some of the patients on oral contraceptives still had recurring endometriomas. Taking oral contraceptives post excision is not a guarantee that you won’t have endometrioma recurrence.

Taking hormonal suppression after surgery is an individual choice, not a requirement.

Some doctors really insist the patient take hormonal suppression to “prevent recurrence” and therefore some patients take hormones even though they don’t want to, or even though the hormones cause them upsetting side effects, because they feel like they need to in order to prevent recurrence.

For superficial and deeply infiltrating endometriosis, there is no solid proof based on good research that hormonal suppression reduces recurrence rates. Even studies on endometriomas don’t all show the same results with hormonal suppression either. (And remember that the studies on endometriomas cannot be applied to superficial or deeply infiltrating endometriosis, because these are different forms of endometriosis. Endometriomas can be responsive to ovarian hormones, and the aim of hormonal suppression post excision would be to suppress ovarian activity.)

Don’t feel like you have to take hormones to prevent endometrioma recurrence because you don’t. You can look at the potential risks vs benefits with your doctor:

  • Did you have an endometrioma excised?
  • How do you tolerate hormonal suppression?
  • Does it cause you a lot of side effects?
  • Have hormones helped your symptoms in the past?
  • Do you want a form of birth control?

Limitations of studies

When looking at studies, it’s important to know that studies can have different limitations and methodologies. Some studies define endometriosis recurrence as visualization of an endometrioma on an ultrasound (this would be actual disease recurrence), while others define recurrence as the return of pain symptoms without actual visual or histological proof of endometriosis, which is quite different because symptoms can return postoperatively due to other pain generators without endometriosis lesions itself actually recurring. In studies, it’s also hard to know if complete or incomplete excision was done during the surgeries – so is it actually recurrence or is it persistence?

Important: as said above, endometriosis is a heterogeneous disease, and endometriomas can be responsive to ovarian hormones. Studies on recurrence or progression are often done on endometriomas because they can be seen on ultrasound. The results of these studies on endometriomas cannot be extrapolated to other types of endometriosis. 


  1. Gałczyński, K., Jóźwik, M., Lewkowicz, D. et al. Ovarian endometrioma – a possible finding in adolescent girls and young women: a mini-review. J Ovarian Res 12, 104 (2019). Accessed Dec 2023.

  2. PAOLO VERCELLINI, SARA DE MATTEIS, EDGARDO SOMIGLIANA, LAURA BUGGIO, MARIA PINA FRATTARUOLO, LUIGI FEDELE. Long-term adjuvant therapy for the prevention of postoperative endometrioma recurrence: a systematic review and meta-analysis. AOGS Volume 92, Issue 1. (2013). Accessed Dec 2023.

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