What causes endometriosis?
The cause of endometriosis is unknown. One theory is that the endometrial tissue is deposited in unusual locations by the backing up of menstrual flow into the Fallopian tubes and the pelvic and abdominal cavity during menstruation (termed retrograde menstruation). The cause of retrograde menstruation is not clearly understood. But retrograde menstruation cannot be the sole cause of endometriosis. Many women have retrograde menstruation in varying degrees, yet not all of them develop endometriosis.
Another possibility is that areas lining the pelvic organs possess primitive cells that are able to grow into other forms of tissue, such as endometrial cells. (This process is termed coelomic metaplasia.)
It is also likely that direct transfer of endometrial tissues during surgery may be responsible for the endometriosis implants sometimes seen in surgical scars (for example, episiotomy or Cesarean section scars). Transfer of endometrial cells via the bloodstream or lymphatic system is the most likely explanation for the rare cases of endometriosis that develop in the brain and other organs distant from the pelvis.
Finally, there is evidence that shows alternations in the immune response in women with endometriosis, which may affect the body's natural ability to recognize and destroy any misdirected growth of endometrial tissue.
What are endometriosis symptoms?
Most women who have endometriosis, in fact, do not have symptoms. Of those who do experience symptoms, the common symptoms are pain (usually pelvic) and infertility. Pelvic pain usually occurs during or just before menstruation and lessens after menstruation. Some women experience painful sexual intercourse (dyspareunia) or cramping during intercourse, and or/pain during bowel movements and/or urination. Even pelvic examination by a doctor can be painful. The pain intensity can change from month to month, and vary greatly among women. Some women experience progressive worsening of symptoms, while others can have resolution of pain without treatment.
Pelvic pain in women with endometriosis depends partly on where the implants of endometriosis are located. Deeper implants and implants in areas with many pain-sensing nerves may be more likely to produce pain. The implants may also produce substances that circulate in the bloodstream and cause pain.
Lastly, pain can result when endometriosis implants form scars. There is no relationship between severity of pain and how widespread the endometriosis is (the "stage" of endometriosis).
Endometriosis can be one of the reasons for infertility for otherwise healthy couples. When laparoscopic examinations are performed for infertility evaluations, endometrial implants can be found in some of these patients, many of whom may not have painful symptoms of endometriosis. The reasons for a decrease in fertility are not completely understood, but might be due to both anatomic and hormonal factors. The presence of endometriosis may involve masses of tissue or scarring (adhesions) within the pelvis that may distort normal anatomical structures, such as Fallopian tubes, which transport the eggs from the ovaries. Alternatively, endometriosis may affect fertility through the production of hormones and other substances that have a negative effect on ovulation, fertilization of the egg, and/or implantation of the embryo.