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).
Typical locations include:
- ovaries: ~75%
- anterior/posterior cul-de-sac: ~70%
- posterior broad ligament: ~50%
- uterosacral ligaments: ~35%
- uterus: ~10 %
- colon: ~5%
Not usually helpful in diagnosis; ~10% of endometriomas can calcify.
The appearances of endometriomas can be quite variable. The classical example is a 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%)
Signal characteristics vary according to the age of any complicating haemorrhage 6:
- 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 for differentiating it from mature cystic teratoma of the ovary
- variable restricted diffusion
- may have wall enhancement
- the presence of an enhancing mural nodule is suggestive of malignant transformation
Treatment and prognosis
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:
- 1. Lee SI. Radiological reasoning: imaging characterization of bilateral adnexal masses. AJR Am J Roentgenol. 2006;187 (3): S460-6. doi:10.2214/AJR.05.2226 - Pubmed citation
- 2. Lee, Susanna I. Imaging Evaluation of Adnexal Masses: Self-Assessment Module American Journal of Roentgenology. 187 (3_Supplement): S457. doi:10.2214/AJR.06.0785 -
- 3. Glastonbury CM. The shading sign. Radiology. 2002;224 (1): 199-201. Radiology (full text) - doi:10.1148/radiol.2241010361 - Pubmed citation
- 4. Levine D, Brown DL, Andreotti RF et-al. Management of asymptomatic ovarian and other adnexal cysts imaged at US: Society of Radiologists in Ultrasound Consensus Conference Statement. Radiology. 2010;256 (3): 943-54. doi:10.1148/radiol.10100213 - Pubmed citation
- 5. Kobayashi H. Ovarian cancer in endometriosis: epidemiology, natural history, and clinical diagnosis. Int. J. Clin. Oncol. 2009;14 (5): 378-82. doi:10.1007/s10147-009-0931-2 - Pubmed citation
- 6. Umaria N, Olliff JF. Imaging features of pelvic endometriosis. Br J Radiol. 2001;74 (882): 556-62. Br J Radiol (full text) - Pubmed citation
- 7. Van Holsbeke C, Van Calster B, Guerriero S et-al. Endometriomas: their ultrasound characteristics. Ultrasound Obstet Gynecol. 2010;35 (6): 730-40. doi:10.1002/uog.7668 - Pubmed citation
- 8. Takeuchi M, Matsuzaki K, Uehara H et-al. Malignant transformation of pelvic endometriosis: MR imaging findings and pathologic correlation. Radiographics. 2006;26 (2): 407-17. doi:10.1148/rg.262055041 - Pubmed citation
- 9. Corwin MT, Gerscovich EO, Lamba R et-al. Differentiation of ovarian endometriomas from hemorrhagic cysts at MR imaging: utility of the T2 dark spot sign. Radiology. 2014;271 (1): 126-32. doi:10.1148/radiol.13131394 - Pubmed citation