Intra-epithelial neuroendocrine carcinoma of the nasal cavity.

We describe a distinctive neuroendocrine carcinoma (NEC) that proliferated intra-epithelially. The tumor was 35 mm in diameter and arose from the right superior turbinate of a 46-year-old woman. Histologically, the tumor exhibited papillary growth and the tumor cells were localized in the thickened mucosal epithelium. The tumor cells had round to oval and vesicular or hyperchromatic nuclei, and cohered without any specific structure such as a fibrillary background, rosette or glandular structure. No stromal invasion by the tumor was observed. Immunohistochemically, the tumor cells were positive for neuron-specific enolase focally. In addition, many tumor cells expressed cytokeratin (AE1/AE3 and CAM 5.2), mostly with characteristic perinuclear dot-like patterns. Electron microscopy revealed focal but well-eveloped cytoplasmic processes containing arrays of microtubules and a few dense core granules. The tumor was considered to be a poorly differentiated neuroendocrine carcinomas (NEC) that exhibited exceptional intra-epithelial proliferation. The tumor completely disappeared after the stereotactic radiosurgery and has not recurred for 40 months. It might be difficult to distinguish a poorly differentiated NEC in the sinonasal region from other neuroectodermal tumors, including olfactory neuroblastoma, but the differential diagnosis is important because each tumor has different clinicopathological characteristics.