Central nervous system extraosseous Ewing sarcoma: radiologic manifestations of this newly defined pathologic entity.

Although these entities are histologically similar, recent advances in molecular genetics have allowed the distinction of central nervous system extraosseous Ewing sarcoma (CNS-EES) from central primitive neuroectodermal tumors (c-PNET) including medulloblastoma and supratentorial PNET. We present 2 cases of pathologically confirmed CNS-EES. Knowledge of CNS-EES as a distinct entity enables the neuroradiologist to suggest the proper diagnosis and the need for special immuno-histochemical and molecular studies to confirm the diagnosis. Because treatment and prognosis are vastly different, the proper diagnosis of CNS-EES versus c-PNET is critical.