Fetal rhabdomyoma.An analysis of nine cases

Nine cases of a distinctive yet uncommon soft tissue tumor are reported with the pertinent clinical and pathologic features. The tumor, which was usually present shortly after birth, occurred, with one exception, in children 3 years of age and under. Male patients outnumbered females 8:1. The lesion was most common in the subcutaneous tissues of the head and neck region, especially the posterior auricular area. The histologic features revealed myoblasts in different stages of differentiation bearing a striking resemblance to fetal skeletal muscle in the 6th to 10th week of development. Electron microscopic study of formalin‐fixed paraffin‐embedded tissue demonstrated unequivocally the striated muscle origin of the tumor. After local excision, none of the tumors recurred in the follow‐up interval, which ranged from 1 to 10 years (median survival 5.5 years). This tumor can be clearly distinguished from the adult rhabdomyoma. The only other neoplasm that may produce some confusion in the differential diagnosis is the well‐differentiated embryonal rhabdomyosarcoma. A means of separating these two entities is discussed.