Inverted (Schneiderian) papilloma

Low power (left panel) and high power (right panel) photomicrographs of inverted papillomas, which usually arise from the lateral nasal wall or paranasal sinuses. They may be entirely endophytic, or they may also have an exophytic component. These lesions may have, albeit rarely, malignant potential. Cytologically, they are composed of non-keratinized squamous cells that preserve scattered mucin-containing cells of the surface during their inverted growth. These appear as mucin-containing "microcysts".