Sinonasal undifferentiated carcinoma: A distinctive clinicopathologic entity

The sinonasal undifferentiated carcinoma (SNUC) is an aggressive and rare n eoplasm arising in the nasal cavity and the paranasal sinuses. To date, ove r 50 cases of histologically proven SNUCs have been reported since its orig inal description in 1986. Presenting symptoms include facial pain, nasal ob struction, diplopia, epistaxis, proptosis, and periorbital swelling. The hi stologic features of this neoplasm include cohesive cells arranged in nests , ribbons, and trabeculae. The cells exhibit hyperchromatic nuclei and a hi gh nuclear to cytoplasmic ratio. A brisk mitotic rate, tumor necrosis, and vascular invasion are prominent features. Confirming the diagnosis of SNUG at the light microscopic level can be challenging, since the microscopic di fferential diagnosis includes olfactory neuroblastoma, rhabdomyosarcoma, un differentiated nasopharyngeal carcinoma (lymphoepithelioma), malignant lymp homa, malignant melanoma, and neuroendocrine (small. cell undifferentiated; oat cell) carcinoma. Sinonasal undifferentiated carcinoma can be different iated from these other neoplasms by correlating clinical, light microscopic , histochemical, immunohistochemical, and ultrastructural characteristics. Aggressive, multimodal therapy can provide the best opportunity for local c ontrol of this neoplastic process, but the optimal treatment has yet to be determined.