Adhesion of shed menstrual tissue in an in-vitro model using amnion and peritoneum: a light and electron microscopic study

We have investigated the adhesion of endometrial tissue isolated from antegradely shed menstrual effluent to amnion and peritoneum. This endometrial tissue was cultured overnight on either side of intact and stripped amnion and on the mesothelial side of peritoneum. Light and electron microscopy were applied to evaluate adhesion. With light microscopy adhesion of endometrial fragments to stripped membranes was observed in nine out of 12 specimens and in 12 out of 13 specimens when layered on the extracellular matrix side of amnion. Adhesion when layered on the epithelial side was seen in only four out of 13 specimens. However, when using scanning electron microscopy adhesion of menstrual endometrial tissue could be visualized in all samples. Numerous adhering fragments were seen when layered on the extracellular matrix side of untreated amnion. On several occasions not only adhesion but also spreading of cells was observed. When layered on the epithelial side of untreated amnion or peritoneum, adhesion was exclusively seen at locations where the epithelium was damaged or absent. These findings were confirmed by transmission electron microscopy. These observations indicate that endometrial tissue isolated from antegradely shed menstrual effluent preferentially adheres to subepithelial structures of amnion and peritoneum. The lack of adhesion to epithelial cells suggests that an intact mesothelial lining prevents adhesion of menstrual endometrial tissue.