Intramuscular myxoma--a clinicopathological study of twenty-three cases.

Twenty-three cases of intramuscular myxoma were analyzed clinically and histologically. The mean age of the patients was 54 years, and two-thirds were women. Clinical follow-up of 2 to 17 years' duration revealed no recurrences or metastases. Intramuscular myxoma thus appears to be a completely benign tumor. One patient simultaneously had a myxoma in the muscle of the thigh and a lesion of fibrous dysplasia in the femur. In addition, 14 of 16 patients studied with x-ray had a significantly higher incidence of minor abnormalities in bones as compared with the normal population. The myxomas were characterized histologically by sparse cellularity, abundant intercellular material digestible with hyaluronidase, and lack of mitotic figures. At the ultrastructural level, the tumor cells showed characteristics of fibroblasts and myofibroblasts. Immunohistochemical analysis of intermediate filament proteins revealed vimentin- but no desmin-positivity in the tumor cells, and endothelial cell markers as well as S-100 protein were absent. This is compatible with fibroblastic-myofibroblastic nature of the myxoma cells.