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.
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