Women's Health

Pelvic Pain & Vulvar Disease Center

Endometriosis

What Causes Endometriosis?

The cause of endometriosis is not known. Several theories exist as to how endometriosis begins, but no one of them seems to account for all cases. During a period most of the menstrual blood comes out through the vagina, but some blood also passes backward through the fallopian tubes into the abdominal cavity. This is called retrograde menstruation. Contained within this menstrual blood are fragments of endometrium, and one theory is that during menstruation some of the menstrual tissue backs up through the fallopian tubes, implants in the abdomen, and grows. This is referred to as the retrograde menstruation or transtubal migration theory. We do not know why these cells seed in some women and not in others. Some experts on endometriosis believe all women experience some menstrual tissue backup and that an immune system problem or hormonal problem allows this tissue to take root and grow in women who develop endometriosis.

Another theory suggests that the endometrial tissue is distributed from the uterus to other parts of the body through the lymph system or the blood system. A genetic theory suggests that it may be carried in the genes of certain families or that certain families may have predisposing factors to endometriosis.

Another theory suggests that remnants of tissue from when the woman was an embryo may later develop into endometriosis or that some adult tissues retain the ability they had in the embryo stage to transform into reproductive tissue under certain circumstances. Surgical transplantation has also been cited as a cause in cases where endometriosis is found in abdominal surgery scars, although it has also been found in such scars when direct accidental implantation seems unlikely.