On a purely mechanical level, endometriosis is caused by endometrial cells, or the cells that usually line the uterus, growing where they shouldn’t. The places where endometrial cells shouldn’t be growing but do include:
Outside of the uterus
Lining of the pelvic area
The endometrial cells that grow outside the uterus then act just like endometrial cells inside the uterus: they thicken, dissolve, and are shed. This process, happening in a part of the body that isn’t designed for it, causes endometriosis. Why those endometrial cells sometimes grow outside of the uterus, though, is less clear. Doctors aren’t completely sure why, but there are a few strong theories.
The Mayo Clinic describes this theory as the most likely cause of endometriosis. Sampson’s theory suggests that endometriosis happens when, during menstruation, menstrual blood which includes endometrial cells gets backed up, and flows backwards up the fallopian tube and into the pelvic cavity. Then, those endometrial cells attach themselves to the outside of the uterus, where they grow.
However, this back-flowing of menstrual blood and endometrial cells is fairly common – much more common than an endometriosis diagnosis.
A complementary theory says that there is an immune system disorder, which may be genetic, since endometriosis sometimes runs in families. The theory says that this immune system disorder gets in the way of the body’s defense when endometrial cells try to implant themselves outside the uterus.
Since most people don’t have this immune system disorder, they’re able to keep the endometrial cells from implanting and growing, and endometriosis doesn’t form.
The base of this theory is that, instead of coming from inside the uterus to implant itself outside, the cells that are already present in the organs outside the uterus are transformed into endometrial cells. This theory suggests that existing cells instead underwent metaplastic changes, perhaps affected by hormones.
The gist of this theory, though, is that existing cells from other organs might change into endometrial cells, and as those endometrial cells grow, they can turn into endometriosis.
This theory suggests that the endometrial cells that start out inside the uterus, exactly where they’re supposed to be, can be transported to different parts of the body through the blood vessels. If they make it into the abdomen through the blood vessels, they can implant on the outside of the uterus and start to grow.
In certain cases, another theory suggests that surgery can cause endometriosis. In these cases, endometrial cells might implant themselves along the surgical incision after a C-section or hysterectomy, and from there they might grow outward. This may then cause endometriosis, though endometriosis after a hysterectomy is only possible in women who did not have both ovaries removed as well.
While it’s not entirely clear why the physical changes that cause endometriosis happen, once endometriosis is diagnosed, there is a strong understanding of what is going on, which is the key piece of information for management and treatment.
“Endometriosis.” MedlinePlus. U.S. National Library of Medicine, September 26 2016. Web.
“Endometriosis: A Guide for Friends, Siblings, and Significant Others.” youngwomenshealth. Boston Children’s Hospital, July 30 2014. Web.
Mayo Clinic Staff. “Endometriosis.” Mayo Clinic. Mayo Clinic, April 2 2013. Web.
- Paul J. Q. van der Linden. “Theories on the pathogenesis of endometriosis.” Human Reproduction. 11 (suppl 3): 53-65. Web. 1996.