A 15-year-old female with progressive myelopathy

March 2005. A 15-year-old female presented with urinary retention, inability to walk and low back pain. MRI disclosed an elongated epidural mass in the thoracic spine with cord compression and invasion into the surrounding bone and soft tissue. Cytologic preparation at intraoperative consultation disclosed a rather monotonous small tumor cells with hyperchromatic nuclei and vacuolated cytoplasm. These vacuoles were best visualized with DiffQuick stain. Pathologic studies revealed an Ewing sarcoma/peripheral primitive neuroectodermal tumor (EWS/pPNET) with typical features including periodic acid Schiff positive diastase sensitive cytoplasmic substance; strong membranous pattern of immunoreactivity for CD99, and a reciprocal translocation of t(11;22)(q24;q12) that was demonstrated by fluorescent in situ hybridization (FISH). The vacuolated cytoplasm was produced by glycogen as demonstrated by electron microscopy. Although primary vertebral EWS/pPNETs are uncommon, they should be considered in the differential diagnoses of extradural/epidural mass of the spine in young patients.