Adenomyosis is a benign uterine condition that involves the invasion of tissue and glands typically confined to the inner mucous membrane of the uterus (termed the endometrium) into the adjacent muscle layer of the uterine wall, the myometrium. The actual incidence of adenomyosis is unknown due to the fact that the condition is often asymptomatic and is very difficult to diagnose, estimates ranging widely from 20 to 65 percent of the female population. When symptoms do occur, they typically consist of abnormal bleeding, cramping, and a distended, tender uterus. Chronic pelvic pain may also develop and intercourse may be difficult. Occasionally the pain associated with adenomyosis may radiate to other nearby areas, especially the lower back. Approximately 80 percent of the time adenomyosis occurs in women that also have another pathologic condition of the uterus, such as endometriosis or the growth of fibroids or polyps. Though the cause of adenomyosis is unknown, other risk factors appear to include childbirth, tubal ligations, Caesarean sections, and termination of pregnancy.