MUSCLE TUMOUR

abnormal tissue growth 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. Although part of the tumour has been known to become malignant, it usually does not spread, nor does it recur once it is removed. The rhabdomyoma is a tumour of striated (striped) muscles. Its most common 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 is soft and 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. Rhabdomyomas of the heart grow in the wall and may project into the heart cavities. Rhabdomyomas affecting other parts of the body commonly involve both the smooth and the striated muscles. Many of these 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. In the prostate they may obstruct the bladder and 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 to sixth decade of life and has usually grown for 10 or more years before it is discovered.