Endometrioma

Endometriomas, also known as chocolate cysts or endometriotic cysts, are a localised form of endometriosis and are usually within the ovary. They are readily diagnosed on ultrasound, with most demonstrating classical radiographic features. 

These occur women of reproductive age.

Endometriomas contains dark degenerated blood products following repeated cyclical haemorrhage. The cysts may be up to 20 cm in size although they are usually smaller (2-5 cm).

Location

Typical locations include:

  • ovaries: ~75%
  • anterior/posterior cul-de-sac: ~70%
  • posterior broad ligament: ~50%
  • uterosacral ligaments: ~35%
  • uterus: ~10 %
  • colon: ~5%
Plain radiograph

Not usually helpful in diagnosis; ~10% of endometriomas can calcify.

Ultrasound

The appearances of endometriomas can be quite variable. The classical example is an unilocular cyst with acoustic enhancement with diffuse homogeneous ground-glass echoes as a result of the haemorrhagic debris. This appearance occurs in 50% of cases 7.

Less typical features include 7:

  • multiple locules (~85% will have <5 locules)
  • hyperechoic wall foci (present in 35%)
  • cystic-solid lesion (~15%) or purely solid lesion (1%)
  • anechoic cysts (rare; 2%)
MRI

Signal characteristics vary according to the age of any complicating haemorrhage 6:

  • T1
    • typically, lesions appear hyperintense while acute haemorrhage occasionally appears hypointense
    • endometriomas with high T1 signal characteristically do not show loss of signal on T1 fat suppressed sequence, which is important to differentiate from mature cystic teratoma of the ovary
  • T2
    • typically hypointense owing to the presence of deoxyhaemoglobin and methaemoglobin (shading sign), which is very suggestive of endometrioma 3
    • T2 dark spot sign is specific for chronic haemorrhage and is helpful in diagnosing endometriomas 9
    • old haemorrhage occasionally appears hyperintense
  • DWI
    • variable restricted diffusion
  • T1C+
    • may have wall enhancement
    • the presence of an enhancing mural nodule is suggestive of malignant transformation

Although endometriomas are usually a benign entity, there is an ~1% rate of malignant transformation. Endometrioid tumours of the ovary and clear cell adenocarcinoma are the most common histological pattern seen 8. They are mostly seen in women >40 years after several years of latency, with endometriomas larger than 9 cm 4-5.  Malignant transformation is uncommon in masses <6 cm.

If not surgically excised, follow-up should be at least yearly 4. GnRH agonists may be used for medical management.

General imaging differential considerations include:

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Article Information

rID: 9042
System: Gynaecology
Section: Pathology
Synonyms or Alternate Spellings:
  • Chocolate cyst
  • Chocolate cysts
  • Endometriomas
  • Endometriotic cyst
  • Endometriotic cysts
  • Endometriomata

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    Case 2: endometrioma, fibroid and ovarian cyst
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    Endometriosis
    Case 7: chocolate cyst in right adnexa
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