Endometrium, squamous morular metaplasia

The epithelium of the endometrium may undergo changes in differentiation either in isolation, or in association with hyperplasia or carcinoma. Squamous morular metaplasia is the formation of inert intraglandular deposits of squamous epithelium. Keratinization is not frequent, and there is usually a rounded/concentric arrangement. Central necrosis can sometimes be seen, as in this case. In this case, the background endometrium is proliferative/disordered with polyp(s).

On their own, squamous morules are benign, although they can recur and cause infertility. When present in clusters, however, they can mimic the complexity and appearance of hyperplasia or carcinoma. A diagnosis of atypical hyperplasia, for example, should not be made unless there is true crowding and atypia of the glandular epithelial component. Because of its tendency to recur, a diagnosis of (benign) squamous morular metaplasia warrants periodic follow-up.