This patient had a right-sided sinonasal mass notable for bone erosion and orbital invasion on CT, marked restricted diffusion on MRI, and intense FDG avidity on PET scan. The findings suggested a highly aggressive and cellular sinonasal malignancy.

The radiological appearance is not specific to particular histopathology but suggests a small round blue cell tumor of the sinonasal tract ¹. This differential includes high-grade carcinomas (sinonasal undifferentiated carcinoma, sinonasal neuroendocrine carcinoma, squamous cell carcinoma, NUT carcinoma), olfactory neuroblastoma (esthesioneuroblastoma), mucosal melanoma, hematolymphoid tumors (lymphoma, plasmacytoma), and sarcomas (Ewing sarcoma/primitive neuroectodermal tumor, rhabdomyosarcoma, mesenchymal chondrosarcoma, small cell osteosarcoma).

An endoscopic biopsy was obtained, with frozen sections showing a small blue-cell tumor. Immunohistochemistry detected diffuse nuclear positivity for the NUT1 protein. The final pathologic diagnosis was NUT carcinoma. NUT carcinoma is a rare, aggressive malignancy that has a predilection for midline sites, is defined by translocations of the NUT (nuclear protein in testis) gene, and carries a poor prognosis.

Co-author: Dr. Francis Deng