Page 12 - Diagnostic delay of endometriosis

concept that endogenous substances released from degenerating menstrual endometrium induce a metaplastic process in coelomic epithelium covering the ovary and the serosa of the peritoneum to develop into endometrial tissue and 3) Sampson’s retrograde menstruation theory, which is currently considered the most widely accepted theory regarding the pathogenesis of endometriosis. According to this theory, reflux of viable endometrial cells through the fallopian tubes occurs during menstruation. Once these cells reach the peritoneal cavity, they can implant, grow and invade into pelvic structures. However, menstrual reflux through the fallopian tubes into the peritoneal cavity is a common physiologic event in all menstruating women with patent tubes, and subtle lesions occur frequently in asymptomatic women.15-17 This has led to the hypothesis that mild peritoneal endometriosis may be considered a temporarily physiologic phenomenon rather than a disease.17 In women with an incapacity to clear the peritoneal cavity, the endometrial cells and lesions may have the opportunity to adhere, vascularize, grow and invade surrounding structures and organs. Why these endometrial cells and implants are resolved by the immune system in some women, whilst other women appear incapable of clearing the peritoneal cavity remains unclear.18 It is suggested that several epidemiological and biological factors affect this process. One of these factors is the reproductive and menstrual pattern of women, which has changed over the last decades, at least in Western nations, due to the decrease in number of pregnancies and duration of breastfeeding, and increased life expectancy. This has led to an increased number of ovulations and menstrual flows, which have been linked to a higher risk of developing endometriosis.19, 20 Other determinants, including (epi)genetic factors and biological factors related to molecular and cellular alterations that favour the progression of cell implantation and growth at ectopic locations may be involved in the development of endometriosis as well.18 Finally, there is accumulating evidence that adult stem cells are involved in the pathogenesis of endometriosis. These cells can either originate from the endometrium or directly from the bone marrow entering the peritoneal cavity by hematogenous or lymphatic dissemination.21 A stem cell origin of endometriosis may be the missing link between some of the previously postulated theories on pathogenesis, since endometriosis could arise from the retrograde menstruation of endometrial stem cells, the dissemination of stem cells derived from bone marrow or endometrium and/or stem cells in persistent Müllerian remnants. Efforts are still being made to further elucidate the exact pathogenesis of endometriosis. This is of major importance, since it may reveal new targets for the development of treatment regimens.
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