Adenomyosis occurs as a result of some of the cells lining the inside of the uterus migrating into the wall of the uterus. Since these cells respond in the same way to the hormones secreted from the ovaries i.e. Oestrogen and Progestrone, it will grow, and bleed a small amount inside the muscles each month. This results in enlargement of the uterus and heavy periods. It may be diagnosed by ultrasound but MRI is more accurate. Medical treatment usually controls the bleeding.