Juvenile rhabdomyoma. An intermediate form of skeletal muscle tumor in children.

Two tumors of the buccal soft tissues in children with rhabdomyomatous features are described and further characterized by immunohistochemical studies in both cases and by electron microscopy in one case. Discrete microscopic nodules of elongated, uniform spindle cells with readily identifiable cytoplasmic cross striations replaced existing normal skeletal muscle. In contrast to fetal rhabdomyoma and embryonal rhabdomyosarcoma, there were no immature mesenchymal cells, nor were there individual rhabdomyomatous cells with short, tapered cytoplasmic processes and overtly malignant cytologic features, including mitotic activity. Following excision, one child remains well 46 months later and the other is doing well 7 months after surgery. Some confusion has been created in the literature by the introduction of the terms cellular rhabdomyoma and myxoid fetal rhabdomyoma. We propose that the so-called cellular fetal rhabdomyoma is distinct from the classic fetal rhabdomyoma and may represent the more differentiated juvenile rhabdomyoma.