Fig. 6.

Oncocytic sinonasal papilloma at low power demonstrates both inverted and exophytic growth (a). The lining epithelium is oncocytic, with cells that have abundant granular eosinophilic cytoplasm and small round nuclei. Like other types of sinonasal papilloma, transmigrating neutrophils and microabscesses are commonly seen (b). Oncocytic sinonasal papillomas frequently exhibit numerous pink microcysts in the oncocytic epithelium. (c) This example of carcinoma ex-oncocytic sinonasal papilloma has a very abrupt transition (arrow) between benign (right) and malignant (left) epithelium (d)