Medically reviewed by Chandre Tina May, Registered Nurse & Menopause Society Certified Practitioner (MSCP). See our editorial policy.
You’ve been handed a diagnosis — or a scan result — that includes the word endometrioma, and maybe someone mentioned “chocolate cyst” in passing, and then the appointment ended. You’re sitting with a strange name, a vague sense of dread, and almost no real information. That is not okay, and it happens far too often to women with endometriosis.
An endometrioma is a specific type of ovarian cyst that grows as a direct result of endometriosis. It is not a rumour, not an overreaction, and not something you should have to decode alone. This post explains what an endometrioma actually is, why it forms, what it can feel like, and what your real options are — in plain language, not medical shorthand.
What’s actually happening: the garden that grows in the wrong place
Think of your uterine lining — the endometrium — as a garden that’s supposed to grow only inside one walled bed. In endometriosis, seeds from that garden escape and take root elsewhere in the pelvis: on the bowel, the bladder, the fallopian tubes, and the ovaries.
When endometriosis tissue settles on an ovary, it responds to your monthly hormonal cycle just as the tissue inside your uterus does — it thickens, breaks down, and bleeds. But because that blood has nowhere to go, it pools inside the ovary and forms a cyst. Over time, the old blood darkens to a thick, dark-brown fluid — which is exactly why clinicians gave it the vivid, slightly unsettling nickname: a chocolate cyst.
The medical term, endometrioma, simply means a cyst made of endometriosis tissue. It is a physical, structural sign that endometriosis is present, and it is visible on an ultrasound scan.
How common are endometriomas?
According to Endometriosis UK, endometriosis affects roughly 1 in 10 women of reproductive age in the UK. Among those with endometriosis, studies suggest that endometriomas develop in a significant proportion — particularly in those with moderate-to-severe disease. They can occur on one ovary or both, and they can range from under a centimetre to several centimetres across.
They are also one of the more frequently missed findings. Because pelvic pain is so often dismissed as “just bad periods,” an endometrioma can quietly grow for years before anyone looks for it.
What does an endometrioma feel like?
The honest answer is: it varies enormously, and that’s part of what makes endometriosis so hard to pin down.
Symptoms you might notice
- Pelvic pain — particularly around ovulation or during your period, often one-sided
- Deep pain during sex — one of the most consistently reported symptoms
- A dull, heavy ache in the lower abdomen that doesn’t fully go away
- Bloating that feels disproportionate to what you’ve eaten
- Fertility difficulties — endometriomas can affect egg quality and ovarian reserve
When there are no symptoms at all
Some endometriomas are found incidentally — during a scan for something else entirely — with the woman feeling no specific pain at the time. This doesn’t mean it isn’t serious or doesn’t warrant attention. It means endometriosis, characteristically, doesn’t follow a predictable script.
If any of this resonates, it’s also worth reading about how endometriosis affects the whole body beyond the pelvis — because the reach of this condition is wider than most people are told.
How is an endometrioma diagnosed?
A transvaginal ultrasound is typically the first-line tool for identifying an endometrioma. An experienced sonographer will look for the characteristic appearance: a smooth-walled cyst with a homogenous, ground-glass internal pattern — the hallmark of old, pooled blood.
MRI may be used for more detail, particularly if the picture is complex. Crucially, a definitive diagnosis of endometriosis itself still requires laparoscopy — keyhole surgery — so the tissue can be directly examined. The scan can strongly suggest an endometrioma, but it cannot confirm endometriosis alone.
Endometriomas are also distinct from other ovarian cysts — such as functional cysts, which often resolve on their own. A functional cyst will typically disappear within a cycle or two; an endometrioma will not. This distinction matters for how it’s managed. For a broader look at how endometriosis is diagnosed and tracked, see understanding endometriosis diagnosis.
What actually helps: your options
Management depends on the size of the cyst, your symptoms, your fertility goals, and your overall picture. There is no single right answer, and any plan should be made with a specialist who knows your case — not applied from a general rule.
Watchful waiting
For smaller endometriomas with manageable symptoms, a specialist may recommend monitoring with regular ultrasound rather than immediate intervention. The garden is being watched, not yet pruned.
Hormonal treatment
Hormonal therapies — such as the combined pill, progestogen-only options, or GnRH analogues — can suppress the hormonal cycle that feeds endometrioma growth and ease symptoms. They do not remove the cyst, but they can slow its progression and significantly reduce pain. A specialist decides which approach fits your situation.
Surgery
For larger cysts, severe symptoms, or when fertility is a concern, surgical removal (cystectomy) via laparoscopy is often recommended. The goal is to remove the cyst wall while preserving as much healthy ovarian tissue as possible. The Menopause Society and NICE guidelines both emphasise that surgery in this area requires careful specialist judgment, particularly regarding ovarian reserve.
It’s worth knowing that endometriomas can recur after surgery, especially if endometriosis itself is not also treated. Recurrence is not a failure — it’s the nature of the condition, and it’s something to plan for with your clinical team.
Pain management — including physiotherapy, nerve pain support, and psychological support — is also a legitimate and important part of care, not a consolation prize. If managing day-to-day symptoms alongside treatment is something you’re working through, managing chronic pelvic pain from endometriosis covers this in more depth.
When to see a doctor
Please don’t wait to be taken seriously — push until you are. See a doctor promptly if you experience:
- Sudden, severe one-sided pelvic pain (a cyst can rupture or cause ovarian torsion — both are medical emergencies)
- Pain that is worsening cycle by cycle
- Difficulty conceiving after six months of trying (or sooner if you’re over 35)
- A known endometrioma that hasn’t been reviewed in over a year
- Any new or changing pelvic symptoms you can’t explain
If you’ve already been told you have an endometrioma and haven’t been referred to a specialist in endometriosis or reproductive medicine, ask for that referral explicitly. You are entitled to specialist care.
Frequently asked questions
Is an endometrioma the same as a regular ovarian cyst?
No. An endometrioma is a specific type of ovarian cyst caused by endometriosis tissue growing on the ovary. Unlike functional cysts, which usually resolve on their own within a few cycles, endometriomas don’t disappear without treatment and can affect ovarian function over time.
Can an endometrioma affect my fertility?
It can. Endometriomas may reduce ovarian reserve — the number of eggs available — and the inflammation they cause can affect egg quality. That said, many women with endometriomas do conceive, naturally or with support. A fertility specialist can give you a personalised picture rather than a general prognosis.
Will it go away on its own?
Unlike some ovarian cysts, endometriomas do not typically resolve on their own. Because they are driven by endometriosis and respond to your hormonal cycle, they tend to persist or slowly grow without intervention. Monitoring and/or treatment with a specialist is the right approach.
Is the “chocolate” colour dangerous?
The dark colour comes from old, altered blood that has pooled inside the cyst over time — it looks like dark chocolate syrup, which is where the nickname comes from. The colour itself isn’t dangerous, but it is a reliable sign that the cyst is an endometrioma rather than another type, and it warrants proper specialist follow-up.
Can endometriomas come back after surgery?
Yes — recurrence is a known feature of endometriosis. Studies suggest endometriomas can return after surgical removal, particularly if the underlying endometriosis isn’t also treated. Hormonal therapy after surgery and regular monitoring are often recommended to reduce the risk of regrowth.
This article is for general information and is not medical advice. It was reviewed by a certified healthcare professional in line with our editorial policy, and we update our content as the science evolves — but every woman’s body is different, so please speak to a qualified healthcare professional about your own symptoms.