Endometrial tissue lines the inside of the uterus. In endometriosis, the same type of tissue also grows in places outside of the uterus.
Implants or patches of endometriosis may develop in the:
Outside surface of the uterus
Pelvis and lower abdomen
Spaces between the bladder, uterus and rectum
Wall of the rectum, bladder, intestines or appendix (less commonly)
Lung, arm, thigh and skin. (This is rare.)
Misplaced endometrial tissue behaves like endometrial tissue in the uterus. It responds to the monthly rise and fall of female hormones. It also can ooze blood during menstruation. This can cause pelvic or abdominal pain.
If the misplaced endometrial tissue enlarges to cover or grow into the ovaries, or if it blocks the fallopian tubes, it can it can interfere with a woman's fertility. .
Endometrial tissue on the ovaries may form into large fluid-filled cysts. These are called endometriomas.
A woman may have an increased risk of endometriosis if:
She has a heavy menstrual flow.
She has a short menstrual cycle (27 days or less).
She has a close female relative with endometriosis.
A woman's risk is probably lower than average if:
She is slightly underweight.
She exercises regularly.
She has had multiple pregnancies.
She has used oral contraceptives.