Endometrial-myometrial interface: Relationship to adenomyosis and changes in pregnancy

The endometrial-myometrial interface (EMI) is an important region of the hu man uterus, which has attracted little research attention. This mucosal-mus cular interface has characteristic features when compared with other simila r interfaces in the human body, It lacks an intervening tissue layer and as a result, the endometrium sits directly on the myometrium rendering it vul nerable to invasion by the endometrium. Both endometrium and myometrium are sensitive to sex steroids, and their structure and function depend to a la rge extent on the sex hormonal milieu, Endometrium, which forms one border of the EMI, is a complex tissue consist ing of several polarized microenvironments. At a cellular level, sex steroi ds interact with local mediators secreted by a variety of cell types and ar e important in maintaining the complex structure and function of the endome trium, Basal endometrium contains prominent aggregates of leukocytes that m ay be important in controlling local cell growth and function, Myometrium also has a distinct zonal anatomy, The recently described juncti onal zone differs structurally and functionally from the outer myometrium, although these functions are not yet clearly understood. Embryologically, i t originates from mullerian ducts together with endometrium, whereas the ou ter myometrium has a non-mullerian origin. During early pregnancy, the EMI is disturbed by invading trophoblast, Alter ations of myometrial intercellular matrix proteins together with expression of appropriate receptors by the trophoblast seem to regulate this unique i nteraction. The EMI also is disrupted in adenomyosis. The sequence of event s taking place at the EMI during development of this pathology is still deb ated, Target Audience: Obstetricians & Gynecologists, Family Physicians Learning Objectives: After completion of this article, the reader will be a ble to describe the endometrial-myometrial interface, including its structu ral and functional features, to summarize the embryologic development of th e uterus and specifically the endometrial-myometrial interface, and to list examples of clinical situations where the endometrial-myometrial interface is disrupted and how these interactions are regulated.