Illustration of three types of uterine fibroma. - at the top, the intramural fibroma is the most common. It forms within the wall of the uterus. - on the right and left, subserosal fibroma which develops outside the uterus on a peduncule attached to the uterus. - in the middle, on the left, a submucosal fibroma which is rarer and forms in the mucus membrane causing heavy bleeding. - in the middle, on the right, a pedunculated submucosal fibroma forms in the mucus membrane inside a pedicle.