What are the causes of endometriosis?

Endometriosis can be roughly divided into three types: implantation theory, serosal theory, and immune theory. Endometriosis actually has a great impact on the health of the uterus. Patients cannot conceive because the uterus is not suitable for pregnancy at this time, so patients need timely treatment to reduce the damage of the disease.

Implantation Theory

As early as 1921, some people believed that the occurrence of pelvic endometriosis was caused by the backflow of endometrial fragments with menstrual blood, entering the pelvic cavity through the fallopian tubes and implanting in the ovaries or other parts of the pelvic cavity. Clinically, during laparotomy during the menstrual period, menstrual blood can be found in the pelvic cavity, and the endometrium can be found in the menstrual blood. The abdominal wall scar formed after cesarean section is a good example of the implant theory.

Serous membrane theory

Also known as the metaplastic theory, it believes that ovarian and pelvic endometriosis arise from the metaplasia of the mesothelial cells of the peritoneum. The paramesonephric duct develops from the primitive peritoneal invagination, and is differentiated from the coelomic epithelium along with the germinal epithelium of the ovary, the pelvic peritoneum, and closed peritoneal invaginations, such as the processus vaginalis (Nook's duct) in the inguinal region, the rectovaginal septum, and the umbilicus. All tissues arising from the epithelium of the body cavity have the potential to metaplasia into tissues that are almost indistinguishable from the endometrium. Therefore, peritoneal mesothelial cells may be easily stimulated by mechanical factors (including fallopian tube ventilation, retroverted uterus, cervical obstruction), inflammation, ectopic pregnancy, etc., and may easily undergo metaplasia and become ectopic endometrium. The germinal epithelium on the surface of the ovary is a primitive coelomic epithelium and has greater potential for differentiation. Under the influence of hormones and inflammation, it can differentiate into various tissues that can be formed during the embryo, including the endometrium. The ovary is the most easily affected site in external endometriosis, which can be easily explained by the metaplastic theory. The implantation theory cannot explain the occurrence of endometriosis beyond the pelvic cavity.

Immunology

In 1980, Weed et al. reported that the ectopic endometrium was infiltrated by lymphocytes and plasma cells, and the macrophages contained hemosiderin deposition and varying degrees of fibrosis. They believe that this is because the ectopic endometrial lesions act as foreign bodies and activate the body's immune system. Since then, many scholars have explored the etiology and pathogenesis of endometriosis from the aspects of cellular immunity and humoral immunity.