Endometrioma (chocolate cyst)

Definition

• An endometrioma is an endometriotic cyst of the ovary, also called a chocolate cyst because of its old blood content.
• One proposed mechanism is invagination of the ovarian cortex with endometriotic implants that fill the cyst with haemolysed blood.

Classification

• Types include cortical invagination cysts, surface inclusion cyst-related and physiological cyst-related endometriotic cysts, and an unclassified type.
• In endometriosis staging, small endometriomas indicate stage III and large ones stage IV.

Occurrence & epidemiology

Epidemiology and pathogenesis

• Endometriomas occur in 17–44% of patients with endometriosis and account for 35% of all benign ovarian cysts.
• The most accepted theory of endometriosis is implantation of endometrial tissue through retrograde menstruation; the disease is oestrogen-dependent.

Clinical features

• The main manifestations of endometriosis are chronic pelvic pain and impaired fertility; adolescents and, rarely, girls before menarche may also have chronic pelvic pain due to an endometrioma.
• Endometriomas can destroy primordial follicles and thus reduce ovarian reserve; occasionally they rupture, causing acute abdominal pain and peritoneal signs.
• Diagnosis is often delayed, by 8–10 years in some studies.

Histology

• An endometrioma is a pseudocyst with a partial or complete endometrial-like lining.
• The ovarian cortex in the cyst wall contains haemosiderin-laden macrophages and fibrotic components.

Diagnosis

Endometrioma on ultrasound

• On ultrasound, an endometrioma typically appears as homogeneously hypoechoic, smooth-walled cyst.
• On Doppler, there is no internal flow, at most delicate peripheral flow.
• According to IOTA, the endometrioma is benign Easy Descriptor without solid components.

Typical imaging findings

• Ultrasound: Within the ovary lies a rounded cyst whose contents are not anechoic but filled with fine, evenly distributed low-level echoes — the ground-glass appearance. The wall is smooth, with no solid nodules and no papillary components.

• On ultrasound, unilocular or few-loculated cysts (fewer than 5 locules) with homogeneous low-level echoes (ground glass) and poor or absent vascularisation are typical.
• On MRI the shading sign due to old blood products rich in iron and protein is specific; the cysts have higher T1 and lower T2 signal than haemorrhagic cysts.
• Enhancing mural nodules are highly suggestive of malignant transformation, as is loss of the typical shading sign.

Keep learning in the app

Further reading (selection)

1. Ovarian endometrioma - a possible finding in adolescent girls and young women: a mini-review (J Ovarian Res 2019, PubMed Central)
2. StatPearls: Endometriosis
3. MSD Manual Professional: Endometriosis
4. DocCheck Flexikon, Endometriom

Cross-references