Tissues normally found in the uterus latch onto other organs and develops into growths. These growths are commonly found in the abdomen and on the ovaries, bowel, and bladder, among other locations. Each month this tissue builds up and breaks down, just as it would in the uterus, which results in bleeding. Because there is no way for the blood to leave the body the result is internal bleeding and often inflammation of the surrounding areas, formation of scar tissue, problems with bladder function, and a host of other problems, depending on the location of the tissue. Even small growths can be extremely painful and problematic.
Endometriosis is the leading cause of female infertility.
When the growths first appear they look like tiny, dark spots scattered around the pelvic area. These small, flat patches are called implants. In some cases, the growths disappear, in others they become scar tissue or don't change at all. Implants are small, flat patches of endometrial cells growing outside the lining the uterus. If endometriosis spreads to the ovaries it can produce cysts filled with blood, called endometriomas, which can range from very small to grapefruit-sized.