endometriosis (ĕnˌdəmēˌtrē-ōˈsĭs) [key], a condition in which small pieces of the endometrium (the lining of the uterus) migrate to other places in the pelvic area. The endometrial fragments may move to the fallopian tubes, ovaries, or other pelvic structures (e.g., the bladder or rectum). The migrated tissue retains its character and changes with the fluctuations of the menstrual cycle, bleeding at the time of menstruation. The blood becomes trapped in cysts that can grow from the size of a pinhead to the size of a grapefruit. Symptoms of endometriosis can be absent or can include painful menstruation, severe abdominal or low back pain, painful intercourse, and rectal bleeding at the time of menstruation. Symptoms often disappear with pregnancy, but 30%–40% of women who have endometriosis are infertile.
The cause of endometriosis is unknown. One hypothesis is that the endometrial fragments move back up through the fallopian tubes rather than leaving the body with the menstrual flow. Diagnosis is by pelvic examination or laparoscopy. Treatment, which depends on the severity of the disease, may include a course of oral contraceptives, or danazol if the patient is trying to conceive. In severe cases surgical removal of the cysts or hysterectomy may be performed.