Endometrial metaplasia

Epithelial metaplasia refers to the replacement of normal epithelium at a given site by mature benign epithelium inappropriate to that site. The endometrium is not unique in that it too demonstrates a spectrum of metaplastic epithelia. Some of these cytoplasmic alterations are better termed “changes” as they are thought not to represent true metaplastic transformation of the endometrial epithelium. The terminology is rather confusing as these two terms have been used interchangeably in the literature. This process may be encountered in benign conditions but can also be seen in association with endometrial hyperplasia and adenocarcinoma. The presence of endometrial metaplasia can significantly complicate the histological interpretation of endometrial biopsy material due to glandular architectural complexity and crowding which can lead to an erroneous diagnosis of endometrial hyperplasia or even carcinoma if the pathologist is unaware of the potential pitfalls. Endometrial metaplasia although commonly seen involving endometrial epithelium, may also on occasions involve the stroma. This review will describe the spectrum of histological features that can be seen in endometrial metaplasia of both epithelium and stroma and will aim to emphasize those histopathological features that will be helpful in distinguishing endometrial metaplasia from hyperplasia and carcinoma.