Microarchitecture of the Human Endometrium by Scanning Electron Microscopy: Menstrual Desquamation and Remodeling

Abstract

Twenty-two hysterectomy specimens were collected over a period of two decades in order to investigate the morphological sequence of menstrual desquamation and its consecutive remodeling of the endometrium. The technique used was described earlier by H. Ludwig and H. Metzger (1976). Scanning electron microscopy is the only way to illustrate and describe the microarchitecture of the endometrial surface. At the beginning of the menstrual bleeding, glandular stumps surviving the desquamation of the layer functionalis stick out from the debris at the top of the basal layer. Fibrin mesh formation, the liberation of lysosomes, and the emigration of white blood cells and macrophages, both being already present in the midluteal endometrial stroma, can be observed. They are interrelated with the clearance of the menstrual wound. Coincidentally with the process of desquamation the re-epithelization starts and takes the first four to six days of the normal cycle. The events are illustrated by selecting specimens of uteri from women with comparable data but from different days of the normal cycle. Surprisingly transitory excess formation of epithelial outgrows (micropolyps) are observed. They disappear later in the cycle, some might persist and form micropolyps, which will be the source of occasional intermenstrual bleeding--so far the polyps are vascularized. The endometrial surface is covered de novo by a lining surface epithelium at the sixth day. Ciliogenesis occurs within this epithelium. Other ciliated cells emanate from the glandular epithelium. In early stages of menstrual regeneration the growth pattern of the epithelial monolayer forming the lining surface in spiral traces according to their origination from the circle-structures of the endometrial glands. Before the incoming menstrual break-down small crevices, clefts or defects appear within the lining surface endometrium, a few white blood cells, enriched in the stroma around the vessels, might even reach the surface. The apical membranes of several non-ciliated cells exhibit rounded leaks, others show ruptures. It is the tissue break-down around the superficial endometrial vessels, what creates the onset of menstrual blood flow. In the very early preparations of the bleeding endometrium those opened capillary vessels could be identified.