Primitive neuroectodermal tumor in sinonasal region.

An elderly woman having a nasal tumor diagnosed as alveolar rhabdomyosarcoma was referred to our hospital. Histological reexamination of the patient revealed that the tumor was composed of lobules of compactly arranged small round atypical cells. The atypical cells contained large oval to round vesicular nuclei, and scanty cytoplasm showing PAS positive glycogen material. The tumor cells were immunohistochemically positive for NSE, S-100 protein and vimentin, but showed negative reaction for myoglobin, desmin, EMA, keratin, LCA, chromogranin and MIC2. Ultrastructurally, the tumor cells contained a few cluster of glycogen particles and less organellae and filaments, and there were no cytoplasmic processes, neurosecretory granules or neurofilaments. Pathological findings suggested primitive neuroectodermal tumor resembling extraskeletal Ewing's sarcoma, but negative reaction for MIC2 immunohistochemically could not ascertain the diagnosis. Location of the tumor and age of the patient of the present case were unusual.