Endometrioma
An endometrioma, sometimes called a “chocolate cyst,” is a type of ovarian cyst that forms when endometriosis tissue grows on the ovary. This tissue behaves like the lining of the womb and can bleed during menstrual cycles, leading to the cyst filling with old, dark blood. Endometriomas are benign but can cause pelvic pain, painful periods, discomfort during intercourse, and sometimes fertility difficulties. They are a marker of more deeply infiltrating endometriosis and often occur alongside other pelvic endometriosis lesions.
Overview | Symptoms & Causes | Diagnosis | Treatment Options
What is an Endometrioma?
The ovaries sit on either side of the uterus and are responsible for storing eggs and producing hormones such as oestrogen and progesterone. A normal ovary forms small cysts every month as part of the menstrual cycle. Endometriomas are different - they are related to endometriosis rather than normal ovarian function.
An endometrioma, often called a “chocolate cyst”, is a type of ovarian cyst formed when endometrial tissue (the tissue that normally lines the uterus) implants on the ovary and grows into a cystic structure. These cysts are filled with old, thick, brown blood, giving them their characteristic appearance.
Endometriomas occur as part of endometriosis, a chronic inflammatory condition where endometrial-like tissue grows outside the uterus. Because this tissue responds to hormonal changes during the menstrual cycle, it repeatedly bleeds and triggers inflammation, leading to cyst formation, scarring, and adhesions.
Understanding Endometriomas
Endometriomas can produce a wide range of symptoms, though some individuals may remain asymptomatic. When symptoms occur, they often overlap with general endometriosis symptoms:
- Pelvic pain, often worse before or during periods
- Pain during sex, particularly deep pelvic pain
- Painful periods (dysmenorrhoea)
- Ovarian cyst–related discomfort, such as a feeling of pressure or bloating
- Difficulty conceiving, as endometriomas can be associated with reduced fertility
These symptoms can overlap with other conditions such as fibroids, pelvic inflammatory disease, and irritable bowel syndrome, so proper assessment is important.
Causes and Risk Factors
Endometriomas occur when endometriosis tissue grows on the ovary and becomes trapped, bleeding each month and gradually forming a cyst. Factors that may increase risk include:
| Endometriosis | The primary cause. Endometrial-like tissue on the ovary bleeds and accumulates over time, forming a “chocolate cyst.” |
| Family history | A genetic tendency can increase the likelihood of developing both endometriosis and ovarian endometriomas. |
| Early onset of periods or short menstrual cycles | More lifetime menstrual cycles increase the chance of retrograde menstruation and ovarian involvement. |
| Not having been pregnant | Pregnancy suppresses ovulation and menstruation; without these breaks, endometriosis activity may be higher. |
| Heavy or painful periods | Often associated with more active or extensive endometriosis, increasing the risk of ovarian cyst formation. |
| Hormonal factors | Higher oestrogen levels can stimulate endometriosis growth, making cyst formation more likely. |
Diagnosing Endometriomas
Diagnosing an endometrioma involves a combination of clinical assessment and imaging, supported by specialist evaluation when needed. Because endometriomas occur within the wider spectrum of endometriosis, diagnosis often focuses on identifying both the cyst itself and any associated pelvic disease.
| Ultrasound | Often the first test used. It can detect endometriomas and other structural changes in the pelvis associated with endometriosis, although small lesions may not be visible. Haemorrhagic cysts can mimic endometriomas, so sometimes a follow-up scan may be suggested to check for resolution. |
| MRI Scan | Used when ultrasound findings are uncertain or when detailed mapping of endometriosis is required. MRI can help further distinguish endometiomas from other types of cyst, and evaluate deep infiltrating endometriosis and pelvic adhesions. |
Treatment Options
Management of an endometrioma depends on symptoms, cyst size, fertility goals, and whether there is associated endometriosis. Many people benefit from a combination of lifestyle measures, medical therapy, and, when appropriate, procedural or surgical options.
Conservative Management
| Pain management | NSAIDs and simple analgesics (pain-killers) can help reduce pelvic pain and period-related discomfort. |
| Hormonal therapy | Aimed at supressing ovarian activity and reducing endometriosis-related inflammation. Options can include: -Combined oral contraceptives -Progestin-only methods such as the minipill, implant, or IUS. -GnRH analogues in selected cases |
| Monitoring | Small, asymptomatic cysts can sometimes be monitored with periodic ultrasound, especially in individuals not currently trying to conceive. |
Procedural Options
| Laparoscopic cystectomy (preferred approach) | Involves removing the cyst, which offers the most durable results and may help improve pain and fertility outcomes. During the procedure, a specialist surgeon can also check for and treat other areas of endometriosis, while taking care to preserve as much healthy ovarian tissue as possible. |
| Drainage or fenestration | Not typically recommended due to high recurrence rates, but may be considered in specific scenarios (e.g., complex anatomy, fertility treatment planning). |
Endometrioma treatment is highly personalised, finding the right balance between symptom relief, fertility goals, and long-term wellbeing. With the right combination of medical support, imaging, and specialist care, most people can achieve effective and sustainable management.
How can Lanthorn help?
Ultrasound Uterus & Ovaries - From £300
A first-line, detailed assessment to identify an endometrioma, evaluate its size and characteristics, and look for signs of associated endometriosis.
Pelvic MRI Scan - £550
Provides a more comprehensive view when the ultrasound findings need further clarification or when deeply infiltrating endometriosis is suspected.
Referral to a specialist
If further assessment or treatment is needed, we can refer you to a trusted gynaecologist or endometriosis specialist for advanced management, including laparoscopic surgery where appropriate
