Fibroids in the uterus. Illustration of a section through the human uterus (pink), showing fibroids (round, whitish). Fibroids are benign tumours consisting of smooth muscle bundles and connective tissue growing slowly in or on the uterine wall. At top are two pedunculated subserous fibroids, which grow on stalks attached to the uterus. There is a pedunculated submucous fibroid inside the uterine cavity causing heavy menstrual bleeding (menorrhagia). Five fibroids are growing within the uterine wall, and there is one in the cervix. Small fibroids usually require no treatment. Large or numerous fibroids may cause obstruction, and can be surgically removed.