Endometrioid carcinoma of the ovary

Last revised by Dr Bahman Rasuli on 24 Nov 2020

Endometrioid carcinomas of the ovary are a sub-type of epithelial ovarian tumors. The vast majority are malignant and invasive. On imaging, they are usually characterized as complex nonspecific solid-cystic masses and found associated with endometriosis

Endometrioid carcinomas account for 8-15% of all ovarian carcinomas. It is considered the second commonest malignant ovarian neoplasm 8

Both endometrioid and clear cell tumors are frequently associated with endometriosis 9

The typical gross appearance of these tumors is similar to that of other epithelial lesions, with variable cystic and solid components. Occasionally, it may be completely solid.

Histologically, an endometrioid carcinoma is characterized by the appearance of tubular glands and bears a strong resemblance to the endometrium. Gross morphological appearance is that of a mass with both solid and cystic areas 2.  Squamous differentiation can be present in more than a third of patients 8.

A benign endometrioid carcinoma is relatively uncommon and when it is benign it tends to be an ovarian cystadenofibroma 3.

  • synchronous endometrial carcinoma or endometrial hyperplasia may be present in up to a third of cases
    • the endometrial abnormality is thought to represent an independent, primary lesion rather than metastatic disease
  • endometrioid carcinoma is the most common malignant neoplasm arising within an endometrioma, although overall this is an uncommon occurrence

Bilateral involvement can be seen in 25-40% of cases 1-2,8.

Imaging findings are often non-specific and include a large, complex cystic mass with solid components.

There may be associated endometrial thickening, evidence of endometriosis or a contralateral mass.

Reported signal characteristics include:

  • T2:
    • relatively low signal intensity of the tumor wall
    • shading sign may be seen 3
  • T1 C + (Gd): can show mild enhancement 3

Endometrioid histology may carry a slightly better prognosis than a serous or mucinous cystadenocarcinoma of the ovary (not a serous tumor in general) independent of stage 5,8. Pure endometrioid tumors carry a far better outcome than a mixed variety.

Metastases to the ovary with colon cancer could be considered especially if the ovarian lesion is bilateral or if there is a known colonic mass, especially due to strong histological similarity. Differentiation from metastatic endometrial cancer can also sometimes be difficult.

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Cases and figures

  • Case 1: endometrioid adenocarcinoma
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  • Case 2: synchronous endometrioid carcinoma of the uterus and ovaries.
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