Benign tumour of muscle fibres in the wall of the womb. Uterine myomas usually occur in the muscular wall of the uterus itself (intramural), but they may also be located below the layer of mucous membrane (submucous) or below the capsule on the outside edge (subserous). The myoma grows in the direction of least resistance and is effectively encapsulated by surrounding tissue. The size of the tumour can vary between a few millimetres and the dimensions of a small football. Sometimes more than one myoma occurs at once. Myomas grow under the influence of oestrogens, therefore do not occur before puberty. A uterine myoma usually becomes smaller after the menopause, and no new myomas then arise. They can increase in size during the first half of pregnancy. Uterine myomas may cause discomfort, but need not necessarily do so; this depends on size and location. Uterine myomas are often discovered by chance. When the myoma is below the layer of mucous membrane, lengthy and copious menstration can occur because the uterus can no longer contract so well. Anaemia can then arise. A uterine myoma does not in itself cause pain, but if the uterus attempts to expel a myoma from the cavity, this can lead to intense cramp. Complications are unusual, and malignant degeneration is extremely uncommon. A uterine myoma can sometimes die if it grows quickly and there is an insufficient supply of blood (during pregnancy or when it turns on its own axis). A large uterine myoma can also lead to complications of presentation: the foetus may enter an abnormal position because of the lack of space. On internal examination the presence of a uterine myoma is detected as a lumpy mass. It is sometimes necessary to perform a laparascopy in order to be certain.