Secondary supratentorial primitive neuroectodermal tumor following irradiation in a patient with low-grade astrocytoma.

We report a case of a supratentorial primitive neuroectodermal tumor (PNET) that occurred 12 years after cranial irradiation for a grade II astrocytoma. Neuroimaging was unable to distinguish between a recurrence of the original neoplasm and the development of a new, distinct entity. Pathologic review assisted by immunohistochemical staining, however, revealed a high-grade PNET. Although rare, PNET needs to be included in the differential diagnoses for previously irradiated patients, who develop recurrent brain tumors in the presence of uncharacteristic imaging features.