Endometriomas: what they are and how I remove them

An endometrioma, often called a chocolate cyst, is a cyst on the ovary caused by endometriosis. Endometriosis is tissue a bit like the lining of the womb, growing in places outside the womb. Inside the cyst is old blood that has turned thick and dark brown, a little like melted chocolate, which is where the name comes from.

When one needs taking out, I do it by keyhole surgery. I gently peel the cyst away from the healthy part of the ovary, use as little heat as I can, close the ovary with fine stitches and add a gel to help prevent scar tissue.

More about endometriosis, and every treatment for it, is on the endometriosis page.

How the cyst forms

Endometriosis on the ovary is thought to bleed a little with each period. Over months, the blood collects in a small pocket inside the ovary. The healthy part of the ovary, which holds your eggs, is stretched thinly around it. The cyst wall sticks closely to that healthy part. The ovary itself is often stuck to the side of the pelvis or to the back of the womb by adhesions, which are bands of scar tissue.

Some women have no symptoms at all, and the cyst is found on a scan done for another reason. Others have painful periods, pain during sex, pain on one side low in the tummy, or find it hard to get pregnant. An endometrioma usually shows up clearly on an internal ultrasound scan, where a slim probe is placed gently in the vagina. At Parkside Hospital and the CRP Clinic I can do the scan during your appointment, so we can talk about what it shows there and then.

Not every endometrioma needs an operation

A small endometrioma that is not causing trouble can often be left alone and checked with another scan later, to make sure it is not growing. Hormone treatment can ease the pain of endometriosis, but it does not make the cyst go away, and you cannot take it while you are trying to get pregnant.

The usual reasons I suggest taking one out are pain, a cyst that is large or growing, any doubt on the scan about what the cyst is, and reasons to do with having a baby, which I explain below. We go through the choices together, including leaving it alone, and then decide together what suits you best. There is no need to decide at the first appointment. The ovarian cysts page explains how other kinds of cyst are checked.

The cancer risk is higher, but cancer is still uncommon

Endometriosis is linked with a higher chance of ovarian cancer. The link is strongest with endometriomas and with deep endometriosis, which is endometriosis that has grown into the tissues of the pelvis rather than sitting on the surface. Researchers in Utah followed 78,893 women with endometriosis and compared them with women without it. Women with endometriomas or deep endometriosis had nearly ten times the risk of ovarian cancer. Even so, ovarian cancer stayed uncommon: about 27 more women in every 10,000 ^[1].

That study watched women over time rather than testing a treatment. So it shows a link, but it cannot tell us whether taking a cyst out lowers the risk. Every cyst wall I remove is sent to the laboratory to be looked at under a microscope, and I go through the result with you.

Surgery, your eggs and getting pregnant

Taking out an endometrioma can make it easier to get pregnant naturally. This is one of the reasons the NICE guideline on endometriosis gives for offering the operation.

The downside is that some eggs are lost, because the cyst wall is so tightly stuck to the healthy ovary. A review brought together 22 studies of IVF (in vitro fertilisation) in women with endometriosis. Women who had an endometrioma removed before IVF had a lower level of anti-Müllerian hormone (AMH, a blood test that gives an idea of how many eggs are left) and, on average, about one fewer egg collected ^[3].

The same review found that taking out an endometrioma before IVF did not make a baby more likely ^[3], although the evidence for this is weak (very low certainty). So if you are going straight to IVF, the cyst does not usually need to come out first, unless it is in the way at egg collection or is causing pain.

Because surgery can lower the number of eggs, I often suggest freezing eggs or embryos before the operation if you would like a family in the future. As an honorary consultant at King’s Fertility, I plan the timing of the surgery and the egg freezing with your fertility clinic.

How I remove an endometrioma

You are fully asleep under a general anaesthetic. I use keyhole surgery, which is how I describe both laparoscopic and robotic surgery, through a small cut in the belly button and two or three small cuts lower down. For more complicated cases, such as a large endometrioma with deep endometriosis around it, I prefer robotic surgery. The camera magnifies the view up to ten times, and the instruments bend like a wrist, which lets me work and stitch precisely deep in the pelvis.

First I gently free the ovary from whatever it is stuck to. Then I open the cyst, wash out the old blood and find the thin layer between the cyst wall and the healthy ovary. I peel the wall away along that layer, taking care to protect as much of the healthy ovary as I can.

I use as little diathermy (heat to seal bleeding blood vessels) as possible, because heat can harm the eggs in the healthy part of the ovary. Instead I stop the bleeding with stitches, and the same stitches close the ovary and bring it back to its normal shape. We also suspend the ovary using temporary stitches that dissolve over time, to help stop it sticking to the sides while it heals. Finally I place a gel that helps stop the ovary sticking down again.

Why I remove the cyst wall instead of draining it

The other way is to drain the cyst and destroy its lining with heat or laser (this is called ablation). A Cochrane review brought together the randomised trials, in which women were chosen at random to have one operation or the other. A year after surgery, the cyst had come back in about 37 in every 100 women after draining and ablation, compared with about 5 to 17 in every 100 after the wall was removed ^[2].

Period pain and pain during sex also came back less often when the wall was removed ^[2]. The trials were small and the evidence is of low certainty, so we cannot be completely sure of these results, and the chance of pregnancy was about the same with both methods.

Recovery and the weeks after

Most women stay one night in hospital and are back to most of their usual activities within two to three weeks. It is common to feel sore for a day or two, and to have pain in the tip of the shoulder from the gas used during surgery. I see you afterwards to go through what I found and the laboratory result.

An endometrioma can come back. We talk together about whether hormone treatment afterwards would suit you, which depends on whether you are trying to get pregnant.

When to seek advice

Go to your nearest emergency department or call 999 if you have sudden, severe pain low in your tummy, especially if you feel sick or are being sick, because an ovarian cyst can sometimes twist or burst.

Book an appointment if:

• a scan has shown an endometrioma or a cyst on the ovary
• you have painful periods, pain during sex or pain on one side low in your tummy
• you are trying to get pregnant and have endometriosis or a cyst

My practice manager, Helen, can send you a secure link to upload any scan reports before your appointment. You can read more on the endometriosis and ovarian cysts pages, or book an appointment.