PELVIC PAIN: ENDOMETRIOSIS endometrium is the lining of the uterus. In some, this tissue grows outside the uterus such as on the ovaries, fallopian tubes, bladder, intestines and other parts. This builds up just like your uterine lining and sheds but unlike uterus, this shed material has no where to go so they build up and can cause pain, blood filled cysts called endometriomas and scarring; this can interfere with conceiving