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Muscle tumours, abnormal tissue growths located in or originating from muscle tissue. Tumours may either arise in muscle tissue or spread to it. Three major tumour types may appear; they are known as leiomyomas, rhabdomyomas, and rhabdomyosarcomas.
The leiomyoma is a tumour of smooth muscles (such as those in the walls of the intestines and of blood vessels). It is most frequently located in the uterus (womb). Leiomyomas have been found in the ovaries, the fallopian tubes, the alimentary canal, the bladder, and the ureters. The tumour is hard or firm, encapsulated, and easily removed. The inside of the leiomyoma appears whorled when cut; there are numerous bundles of muscle fibres interlacing in various planes. The tissue may contain crystals or may become totally calcified so that it is converted into a mass of stone. Although part of the tumour has been known to become malignant, it usually does not spread out of the uterus or recur once it is removed. The rhabdomyoma is a tumour of striated (striped) muscles. Its commonest location is the heart. Some forms of the tumour do spread: metastases (secondary tumours at distant sites) have been found in the uterus, the bladder, the prostate, the esophagus, the digestive tract, the sex glands, and the kidneys. The tumour may be in nodes, flat masses, round clusters, or polyps. Sometimes it is closely contained in the tissue, and at other times it may be diffuse and difficult to remove. The tissue of the rhabdomyoma is soft and gray, with strands of white fibres; some tumours take on a reddish-yellow appearance. The cells are generally large with a spider- or spindle-shaped appearance.
Rhabdomyomas of the heart grow in the wall and may project into the heart cavities.
The tissue invaded is loose and vacuolated (with large spaces). It is thought that the tumour is a result of an embryologic disorder in the development of the heart. Rhabdomyomas affecting other parts of the body commonly involve both the smooth and the striated muscles. Many of the mixed tumours are likely to be malignant and may grow to great proportions. Tumours of this type appearing in the uterus, the vagina, or the prostate are large and polyp- shaped masses that protrude from these structures; occasionally they rupture, giving off blood and malodorous discharges. In the prostate they may obstruct the bladder. The prostate tumours may be found at birth, in early childhood, or, more rarely, in the adult. Their symptoms are fever, difficulty in urinating, and a general wasting away. They tend to invade the adjacent pelvic tissue.
The rhabdomyosarcoma is extremely malignant; it arises in the skeletal muscles of the body. Most tumours of this type are located in the leg or arm muscles. The rhabdomyosarcoma usually recurs even after amputation of the involved extremity.
The tumour itself is generally the only clinical symptom; it appears most often in the fifth or sixth decade of life. It is soft and often necrotic (showing degeneration) or hemorrhagic. The amount of bleeding determines the colour, which varies from pale yellow to pink or dark red. The tumour is removed as soon as it is found, Radiation does not seem to be of much help. The tumour has been estimated to grow 10 or more years in most cases before it is discovered.
