Primary rhabdomyosarcoma of brain and cerebellum. Report of four cases in infants: an immunohistochemical study.

Tumors of the central nervous system (CNS) composed of pure mesenchymal derivatives with both embryonal and mature striated muscle cells devoid of neuroblastic elements should be considered rhabdomyosarcomas. Some 13 cases have been reported, and here we study four additional cases in infancy under 3 years of age which represent 0.82% of 483 intracranial tumors studied by us at the Children's Hospital in the last 12 years. Two cases were localized in the temporal lobes, and two were in the cerebellar vermis. All of them were typical embryonal rhabdomyosarcomas at various stages of differentiation including undifferentiated mesenchymal cells, embryonal cells, and rhabdomyoblasts. Tumor cells achieved a higher degree of differentiation in the cerebellum, as shown by readily detectable immature muscle fibers which were consistently absent in tumors involving the brain. Myoglobin [peroxidase-antiperoxidase (PAP) technique] was positive throughout in rhabdomyoblasts and in immature muscle cells, whereas glial fibrillary acidic protein was negative in all four tumors. In spite of the well differentiated appearance of the cerebellar tumors, their behavior was highly malignant with extensive infiltration of brainstem leptomeninges in one case, and all patients survived for only a short time after surgery. These tumors may be observed in the midline structures of the posterior fossa and in the brain, but we suspect their true incidence might be higher if immunohistochemical techniques were applied.