What causes endometriosis?

Sex hormones must play a significant role in endometriosis as the condition is not found before the onset of menstruation and is rare after the menopause. Removing the ovaries usually cures endometriosis.

The origin of endometriosis remains an area of debate. No single theory explains all aspects of endometriosis so there is presumably more than one cause. The implantation theory remains the most likely explanation for the majority of occurrences. During a period, although most of the blood is passed out through the vagina, some passes in a retrograde fashion up through the Fallopian tubes and into the peritoneal cavity (Figure 23.2). Some of this blood will contain live endometrial cells, which can implant on to structures around the pelvis. This would explain why the most common sites of endometriosis are the ovaries and the pouch behind the uterus where the fluid will collect as a result of gravity. As a result of effective contraception and reduction of breast feeding, women today experience a ten-fold increase in the number of periods they experience compared to their great-grandmothers. This may explain the increased incidence of endometriosis.

Other theories include:- Coelomic metaplasia and changes in the immune system. "metaplasia" refers to the transformation of one kind of tissue into another. Coelomic metaplasia refers to cells that transform into endometrial cells, perhaps as a result of chronic inflammation or irritation from retrograde menstrual blood. There may be a genetic predisposition.

The transplantation theory - That Endometriosis spreads via the circulatory and lymphatic system.

Latrogenic transplantation - Endometriosis is accidentally transported during surgery. Endometriosis occasionally occurs in wounds following caesarean section or hysterectomy

Coelomic metaplasia - This theory holds that certain cells, when stimulated, can transform themselves into a different kind of cells.

The hereditary theory - Women with family members who have Endometriosis are more likely, or are susceptible to developing the disease. Studies of twins have shown that there is a genetic predisposition to endometriosis. At one time it was thought that Caucasian women were more susceptible than others but the latest data shows that the only group with a genuine increased incidence is the Japanese. African women seem to be at lower risk.

Auto-immune disorder - Of all the theories being postulated for the cause of Endometriosis, the idea that this disease is an autoimmune disease seems the very likely, credible and feasible. Autoimmune diseases are now widely believed to occur based on genetic predisposition that may be triggered by environmental and other external factors.

Thin women seem to be more at risk. Endometriosis is more common in those who have not been pregnant.

If deposition of live endometrial cells in the peritoneal cavity is a common, monthly occurrence, why do the majority of women have just a few tiny spots of endometriosis at most, whilst others have severe disease? It is likely that there are a variety of mechanisms which can facilitate the development of endometriosis and others that remove endometriotic deposits. The effectiveness of these mechanisms must vary between individuals. It would seem that there is a normal dynamic process so that small endometriotic deposits develop and are then removed by natural processes. The tiny spots of endometriosis so frequently seen at laparoscopy may be a normal event that nature will usually remove without intervention. Some experts now question whether minimal endometriosis is a disease or just a normal biological process.

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