Rare lesions in the pathologic examinations of endometriosis.

To be familiar with some unusual histologic appearances with endometriosis would serve to make prediagnosis of premalignant or a malign disease.

Key Points

Importance:

• It would be wrong to consider endometriosis as a premalignant lesion, but despite its relatively low incidence, it still has the potential to develop a malignancy.

Highlights:

• In most cases, the histopathologic definition of endometriosis is endometrioid type glands with stroma often associated with pigment-laden macrophages. 
• In some cases the presence of polypoid endometriosis, stromal endometriosis, mesothelial hyperplasia associated with endometriosis and atypical endometriosis may result in diagnostic problems.

What's done here:

• In this review, the expert author underlined unusual lesions that can arise in endometriosis by giving examples through histologic knowledge and pointed out the misinterpreted or overlooked pathologies during the endometriosis diagnosis. 

Unusual endometriosis database:

• Stromal endometriosis: the absence of the glands is the characteristic feature.
• Mesothelial hyperplasia associated with endometriosis: This is a common lesion where we can notice it on ovarian surfaces and peritoneum in case of pelvic inflammation, tuba-ovarian abscess, torsion, endometriosis, and ovarian tumors.
• Atypical endometriosis: Not a well-defined universal entity, but mostly a degree of nuclear atypia or an endometrial hyperplasia-like lesion is found in atypical endometriosis involving the epithelial lining of ovarian endometriotic cysts.
• Polypoid endometriosis: This rare condition consists of focal endometriosis forming a mass that resembles endometrial polyp microscopically.
• Risk of neoplastic transformation of endometriosis: This has been estimated to occur 1% of ovarian endometriosis.
• Endometriosis associated ovarian neoplasms: The rare tumors arising in endometriosis. The most common are endometrioid carcinoma and clear cell carcinoma of ovaries. Adenocarcinoma, low grade endometrial stromal sarcoma, and carcinosarcoma could also be seen, but even less. Furthermore, in ovarian endometrioid carcinomas, some pathologic alterations like metaplastic and cytoplasmic changes, sex-cord like formations, and spindle cell differentiation, and immunohistochemical pitfalls may occur while diagnosing endometrioid carcinomas. 

Lay Summary

Dr. Glenn McCluggage from the Department of Pathology, Belfast Health, and Social Care Trust, penned a review about selected uncommon variants of endometriosis or benign alterations that may cause difficulties of pathologic diagnosis and provided all related histopathological illustrations in a recent periodical of Histopathology.

The potency of some endometriosis undergoing a malignant transformation like ovarian clear cell carcinoma and endometrioid is well known. Besides them, uncommon tumor types that may arise in endometriosis also be under debate.

The author shared some of this own pathological illustrations just to make clear some of the overlooked or misinterpreted pathologies throughout the diagnosis of endometriosis.

After describing the benign pathologic conditions that can take place in some of the endometriosis cases which are atypical, polypoid, stromal endometriosis and mesothelial hyperplasia associated with endometriosis he attracted the attention to the risk of neoplastic transformations in endometriosis. 

The morphologic appearance of endometrioid carcinoma in the ovary can be confusing when compared with uterine corpus endometrioid ca. or other primary ovarian tumors and metastatic adenocarcinomas. The presence of foci of typical endometrioid carcinoma, endometriosis, adeno-fibromatous areas, and squamous elements altogether shaped the suspicion about the diagnosis.

The occurrence of clear cells in ovarian endometrioid carcinoma is common while immunohistochemistry has a limited value in distinguishing between clear cell areas within an endometrioid carcinoma.

To clarify the diagnosis of endometrioid carcinoma some Mullerian markers like CK7, PAX8, CA125, and ER are helpful as well as CK20, CDX2, SATB2, thyroid transcription factor 1, and WT1.

Other rare ovarian tumors like somatically derived from yolk sac (YST), seromucinous neoplasms, mesonephric like carcinoma are widely discussed in this paper and supported with their literature reviews.

Research Source: https://www.ncbi.nlm.nih.gov/pubmed/31846535