Intracranial Ewing sarcoma/'peripheral' primitive neuroectodermal tumor ofdural origin with molecular genetic confirmation

Ewing sarcoma/'peripheral' primitive neuroectodermal tumor (ES/pPNET) is th e designation given to a family of small cell neoplasms that typically aris e in bone or soft tissue and are unified by their common expression of the MIC2 antigen and specific translocations involving a gene on chromosome 22q 12 [the most common being t(11;22)(q24;q12)]. ES/pPNET of intracranial orig in is extraordinary. We report the case of a 6-year-old boy with a large le ft frontal region mass that adhered to dura and was extracerebral at surger y. Histologic study revealed a high-grade, undifferentiated-appearing neopl asm of small cell type that was negative on immunostudy for glial fibrillar y acidic protein, synaptophysin, desmin, leukocyte common antigen, smooth m uscle actin and epithelial membrane antigen, but positive for vimentin and neuron-specific enolase and diffusely labeled by antibody O13 (which recogn izes the MIC2 gene product). RNA-based polymerase chain reaction assay conf irmed the diagnosis of ES/pPNET by demonstrating fusion transcripts indicat ive of t(11;22) translocation. Bone scan, computerized tomography of the ch est and bone marrow examination revealed no systemic tumor. The limited obs ervations published to date suggest that primary intracranial ES/pPNET is m ost likely to present in childhood as a circumscribed, contrast-enhancing a nd dural-based extracerebral mass. It must be distinguished from a variety of small cell neoplasms, particularly PNETs of central neuroepithelial orig in.