Endometrioma on Ultrasound: What Does a Chocolate Cyst Mean?

An endometrioma on ultrasound is a cyst on or in an ovary that has the typical look of an endometriosis cyst. It is often called a chocolate cyst because it is usually filled with thick, brown fluid made of old blood. It suggests endometriosis is affecting the ovary, and the next step depends on your symptoms, the cyst's size and whether pregnancy is a goal.

Cleveland Clinic cites estimates that between 17 and 44 in 100 people with endometriosis develop an ovarian endometrioma. A cyst can be very small or large, and it can affect one or both ovaries.

This guide helps you understand an existing scan report and prepare questions. It cannot confirm what your cyst is or decide on treatment for you.

A cyst can rarely burst or twist the ovary and cut off its blood supply (torsion). Healthdirect describes torsion, bleeding and rupture as medical emergencies. Do not wait for a planned follow-up scan if any of these happen:

• Sudden, severe pain in the pelvis or lower tummy.
• Pelvic pain with feeling faint, dizzy or weak.
• Pain with fever or vomiting.
• Pelvic pain with heavy vaginal bleeding, especially if you could be pregnant.

A transvaginal ultrasound, where a small probe is placed in the vagina, usually gives the clearest view of the ovaries. MRI is sometimes used as well to show a cyst's size and location.

An international consensus statement on ovarian tumour ultrasound (ESGO, ISUOG, IOTA and ESGE, 2021) describes the typical endometrioma as a cyst with one to four compartments (locules) and 'ground-glass' contents. That phrase means evenly spread, faint internal echoes from old blood. Most typical endometriomas show no blood flow inside the cyst on Doppler. The same statement notes this pattern is typical in people who have not reached menopause.

Reports may also use terms such as unilocular, low-level echoes, avascular or O-RADS. The related guide on ovarian cysts on ultrasound explains these risk categories in more detail. If your report says 'atypical', 'solid component' or 'internal vascularity', ask what that means for you, because those words can change the plan.

Endometriomas are linked to endometriosis, a condition where tissue similar to the womb lining grows elsewhere, often on the ovaries, fallopian tubes and pelvic lining. NHS lists common symptoms such as severe period pain, pelvic pain, pain during or after sex, and pain when passing urine or stool.

An ultrasound finding is not the whole picture. The European Society of Human Reproduction and Embryology (ESHRE) guideline recommends ultrasound or MRI as part of the assessment, but says a normal scan does not rule out endometriosis, especially small surface areas. Cleveland Clinic notes that a removed cyst is sometimes sent to a laboratory to confirm what it is. NHS describes medicines as the usual first treatment, so an operation is not always the first step.

CA-125 is a blood protein. MedlinePlus lists endometriosis, fibroids, pelvic inflammatory disease, liver disease, periods and pregnancy among the non-cancer reasons it can be raised. The ESGO/ISUOG/IOTA/ESGE consensus statement lists a raised CA-125 among the typical features of an endometrioma.

That means a raised result alongside a typical-looking cyst is common and does not by itself point to cancer. ESHRE recommends against using blood biomarkers to diagnose endometriosis. Reference ranges differ between laboratories, so compare your result with the range printed on your own report. See the high CA-125 guide for more on how the test is used.

Cancer arising from an endometrioma is rare. ESHRE says endometriosis is linked to a higher rate of ovarian cancer, but the increase in absolute risk compared with the general population is low, and it does not recommend extra cancer screening for everyone with endometriosis. Your team may watch more closely if a cyst changes, develops solid areas or is found after menopause.

Pregnancy is possible with an endometrioma. Cleveland Clinic notes it may be more difficult depending on the cyst's size or if both ovaries are affected. Healthdirect also says these cysts may make it harder to conceive.

Surgery is where fertility questions matter most. ESHRE does not recommend routinely removing an endometrioma before IVF or other assisted reproduction, because surgery is likely to reduce ovarian reserve, meaning the supply of eggs. Surgery may still be considered to relieve pain or to make eggs easier to reach. A blood test called AMH is often used to estimate ovarian reserve, but it does not predict whether you will get pregnant. The low AMH guide explains its limits.

NHS notes that hormonal treatments for endometriosis are not used while trying to conceive, and that referral to a fertility specialist is available.

There is no single plan for every endometrioma. Options described by Cleveland Clinic and NHS include:

• Monitoring with repeat scans, often for small cysts that cause no symptoms. ESHRE says routine ultrasound monitoring of endometriosis without symptoms can be considered.
• Medicines, such as pain relief and hormonal treatments, to manage symptoms when pregnancy is not the current goal.
• Surgery, usually keyhole, when a cyst is painful, growing or large, or when the appearance is uncertain. ESHRE recommends removing the cyst wall (cystectomy) rather than only draining it, with care taken to limit damage to the ovary.
• Endometriomas can come back after treatment, so follow-up is often part of the plan.

Take your full scan report and any blood results to the appointment. These questions can help:

• Does my report describe a typical endometrioma, or are there features that need a closer look?
• How big is the cyst, and is it on one ovary or both?
• Do I need a repeat scan, and when? What change would alter the plan?
• What does my CA-125 result mean alongside the scan?
• If I may want to get pregnant, how would surgery affect my ovary, and should ovarian reserve be checked first?
• Which symptoms mean I should seek urgent care rather than wait?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a similar scan report weighed monitoring, hormonal treatment or surgery can help you notice questions you had not thought of, such as fertility plans or recurrence. Each case is different, and nothing you read there replaces advice from the clinician who knows your history and has seen your images.