Adenomyosis is a non-cancerous disease of the uterus in which in inner lining of the uterus, the endometrium, is found within the muscular layer of the uterus, the myometrium. The cause of adenomyosis is unknown. The most common symptoms associated with adenomyosis are abnormal uterine bleeding, usually in the form of heavy and/or prolonged bleeding, and pelvic pain, especially during bleeding. The only definitive treatment is hysterectomy (removal of the uterus).