Schneiderian papilloma of the sinonasal tract.

The sinonasal tract, lined by ciliated respiratory mucosa (Schneiderian epithelium), gives rise to three distinct papilloma morphologies. Collectively, these lesions are referred to as Schneiderian papillomas and include inverted (∼50%), exophytic (∼47%), and oncocytic (∼3%) types. The tumors are uncommon, with an incidence of about 2.3 cases per 100,000 population. The lesions develop over a broad age range but peak in the fifth decade, with males affected more often than females (3:1). Malignant transformation develops in about 2% of Schneiderian papillomas.