What is endometriosis?
Endometriosis is the abnormal growth of endometrial tissue similar to that which lines the interior of the uterus, but in a location outside of the uterus. Endometrial tissue is shed each month during menstruation. Areas of endometrial tissue found in ectopic locations are called endometrial implants. These lesions are most commonly found on the ovaries, the Fallopian tubes, the surface of the uterus, the bowel, and on the membrane lining of the pelvic cavity (i.e. the peritoneum). They are less commonly found to involve the vagina, cervix, and bladder. Rarely, endometriosis can occur outside the pelvis. Endometriosis has been reported in the liver, brain, lung, and old surgical scars. Endometrial implants, while they may become problematic, are usually benign (i.e. non-cancerous).
What causes endometriosis?
The cause of endometriosis is unknown. One theory is that the endometrial tissue is deposited in unusual locations by the retrograde flow of menstrual debris through the Fallopian tubes into the pelvic and abdominal cavities. The cause of this retrograde menstruation is not clearly understood. It is clear that retrograde menstruation is not the only cause of endometriosis, as many women who have retrograde menstruation do not develop the condition.
Another possibility is that areas lining the pelvic organs possess primitive cells that are able to develop into other forms of tissue, such as endometrium. (This process is termed coelomic metaplasia.)
It is also likely the direct transfer of endometrial tissues at the time of surgery may be responsible for the endometriosis implants occasionally found in surgical scars (for example, episiotomy or Cesarean section scars). Transfer of endometrial cells via the bloodstream or lymphatic system is the most plausible explanation for the rare cases of endometriosis that are found in the brain and other organs remote from the pelvis.
Finally, there is evidence that some women with endometriosis have an altered immune response in women with endometriosis, which may affect the body’s natural ability to recognize ectopic endometrial tissue.
Endometriosis and Infertility
Endometriosis can be associated with severe pain and fertility problems. About 30% to 40% of women with endometriosis have some trouble conceiving. The reason for this is not well understood, and scarring of the reproductive tract, or hormonal factors may be involved. Over time endometrial implants may grow, or cysts may result because of endometriosis, which also may cause fertility problems.