Endometriosis Causes
What Causes Endometriosis?
The term endometriosis is used to describe the presence of endometrial tissue outside the uterine cavity. The first morphologic description of the condition was made in 1690 by Daniel Schroen, a German physician, on a skin lesion. In 1860, Carl von Rokitansky, an Austrian physician and pathologist, first presented endometriosis from a pathological point of view.
Despite intensive research around the world and the long history of the condition, a unified root cause of endometriosis is still not 100% evident and to date, there is not one single universally accepted theory that explains all cases. This is most likely because endometriosis does not have a single disease pathway, a fact that is reflected by the many different clinical manifestations of the disease, the different areas of the body affected by it, the different levels of severity and the different symptoms experienced by many women. The complexity of the condition and its many different presentations suggest that many different factors may play a part.
Different forms of endometriosis are currently recognised and they may develop in different ways. These are typical or peritoneal endometriosis, cystic or ovarian endometriosis and deep infiltrating endometriosis, where nodules infiltrate other pelvic organs, most commonly the bowels, bladder and pelvic ligaments.
Common to all theories, is that oestrogen is required for endometriotic lesions to grow and expand. That is why endometriosis is hardly ever seen in young girls before they start menstruating and no lesions are seen in women who have reached menopause.
The main theories proposed by scientists and researchers are:
Retrograde menstruation
One of the most recognised theories assumes that the cause of endometriosis has to do with so-called retrograde menstruation. Every time a woman has a period, cells from the endometrium inside the uterus shed and come out with the menstrual flow. Part of that flow moves backwards through the Fallopian tubes and reaches the pelvis and abdomen. While this might sound strange and unusual, 9 out of 10 women experience retrograde menstruation. This process does not only occur during the menstrual period, but also in between periods during the menstrual cycle. Shortly before ovulation, the uterus generates suction whereby endometrial cells (as well as sperms) are drawn into the fallopian tubes.
Some of the endometrial cells that reach the abdominal cavity, manage to implant into the pelvic and abdominal organs and continue to grow, generating the ectopic endometrial implants. This phenomenon has been demonstrated in animal models with the main experiments conducted in baboons.
Coelomic metaplasia
This theory states that endometriosis directly develops on the affected regions outside the uterus from cells already present in areas such as the pelvic peritoneum, ovaries, recto-vaginal septum, bladder and bowel. Cells within these areas have the same embryonic origin as the endometrial cells, and under specific circumstances, can transform into endometrial cells and become endometriosis. This theory is believed to explain how endometriosis can develop in areas distant from the pelvis such as the diaphragm and lungs.
Immunologic and genetic theories
Other explanations state that endometriosis has to do with changes in the immune system. Antibodies against endometrial cells can be found in the blood which then lead to an immune response and inflammation in the affected areas damaging surrounding tissues. However, it is still unclear whether this immune change causes endometriosis or whether it is a response to endometriosis that was already present in the body.
Endometriosis occurs more often in certain families than others. Women with a close female relative with endometriosis such as the mother or sister, have an increased risk of up to seven times of developing endometriosis suggesting a genetic predisposition. To date, no specific ‘endometriosis gene’ has been identified and the mechanism is believed to be multifactorial or polygenic.
Genetic/Epigenetic theory
This most recent theory suggests that endometriotic lesions can originate from endometrial, bone marrow or stem cells that have inherited genetic and/or epigenetic defects.
According to the theory, most women develop microscopic endometriotic lesions. These can either regress spontaneously or progress into bigger lesions depending on additional factors.
This theory is similar to the one used to explain multistep development of some tumours.