The role of the peritoneum in the pathogenesis of endometriosis.

BACKGROUND Endometriosis affects 6-10% of women of reproductive age and is associated with chronic pelvic pain, dysmenorrhoea, dyspareunia and infertility. Endometriosis is defined by the presence of endometrial tissue outside the uterus, most commonly attached to the pelvic peritoneum. The endometrium in women with endometriosis is reported to be altered and there is increasing evidence that the phenotype of the pelvic peritoneum may also play a role in the establishment and maintenance of the disease. The aim of this review is to discuss the putative role of the pelvic peritoneum in the pathophysiology of peritoneal endometriosis. METHODS A review was undertaken of the published literature on (i) the anatomy and physiology of the peritoneum and (ii) the potential roles played by peritoneal cells in the establishment and maintenance of peritoneal endometriosis. The current understanding of the biology of peritoneal endometriosis is summarized and the potential interaction of the peritoneum with ectopic endometrial cells in endometriosis is highlighted. RESULTS Several studies indicate that differential expression of peritoneal mesothelial adhesion factors occurs in women with endometriosis, providing potential ectopic endometrial cell attachment sites for the establishment of endometriosis lesions. Changes in the peritoneal mesothelial cell phenotype, including loss of tight junctions, may allow ectopic cells to bind to, or early lesions to invade into, the extracellular matrix. Epithelial-to-mesenchymal transition of peritoneal mesothelial cells may also lead to an increase in lesion invasion and formation of fibrotic tissue in and around the lesion. There is evidence that the peritoneal mesothelium may also play a role in the invasion potential of ectopic cells by production of MMPs increasing local tissue remodelling. Peritoneal immune scavenging function may be lowered in women with endometriosis; for example there is a notable increase in macrophage-derived secretion products in women with endometriosis associated with increases in cell proliferation, cell adhesion and neovascularization. CONCLUSIONS The pelvic peritoneum appears to play a key role in the development and maintenance of endometriosis.