POLYPHENOTYPIC SMALL-CELL ORBITOCRANIAL TUMOR

A male infant was born with a massive orbitocranial tumor without evid ence of metastasis. On light microscopy, the histologic pattern of the tumor was that of a largely necrotic and highly undifferentiated smal l round cell neoplasm of uncertain origin. Ultrastructural features of the primitive cells included a rare tight junction and myofibril. Imm unohistochemical studies showed positive staining for cytokeratin, vim entin, muscle-specific actin, neuron-specific enolase, and S100 protei n and negativity for desmin and leukocyte common antigen. We believe t his case represents an example of a polyphenotypic small-cell tumor of childhood with epithelial, rhabdomyoblastic, and neuroectodermal diff erentiation.