Undifferentiated carcinoma in oncocytic Schneiderian papilloma. A rarity.

The term Schneiderian mucosa refers to the ectodermally derived lining of the nasal cavity and paranasal sinuses, composed generally of stratified ciliated columnar cells, loose abundant lamina propria, and minor salivary glands and their ducts. This unique mucosa may give rise to three distinct histomorphologic papillomas collectively called Schneiderian papillomas. Hyams has described these variants and categorized them as inverted, fungiform (exophytic, squamous) and oncocytic Schneiderian papilloma (cylindrical cell papilloma) based on their pattern of growth. Schneiderian papillomas are uncommon, representing only 0.4%--4.7% of all sinonasal tumors. Oncocytic Schneiderian papillomas are the rarest of the three morphological variants, accounting for only 3 per cent of all sinonasal papillomas. Sinonasal papillomas have a small but distinct risk of malignant transformation. Here, we report a case of undifferentiated carcinoma arising from oncocytic Schneiderian papilloma (OSP). To the best of our knowledge, the current patient is the fourth reported case of undifferentiated carcinoma arising in OSP in English literature.