Answer: Schneiderian papilloma, cylindrical cell type

Histology: The lesion has a prominent exophytic growth: folds of mucosa are thrown into papillary projections. These projections are lined by a multilayered oncocytic epithelium. The cells have abundant pink granular cytoplasm and uniform round nuclei with prominent nucleoli. The epithelium is heavily infiltrated by neutrophils that form numerous intraepithelial microabscesses. Within these areas are intraepithelial mucinous cysts that are reminiscent of certain fungal organisms (i.e. Rhinosporidium).

Discussion: Schneiderian papillomas are neoplastic proliferations of the ectodermally-derived Schneiderian mucosa lining the sinonasal tract. Three variants are recognized: fungiform, inverted, and cylindrical (oncocytic). The cylindrical cell variant of Schneiderian papilloma variant is the least common. It is architecturally characterized by multilayered papillary epithelial proliferations, and cytologically by oncocytic appearing cells with associated intraepithelial mucin cysts containing pink acellular material. These cysts should not be mistaken for sporangia of rhinosporidiosis.

In addition to the propensity for disease recurrence following incomplete excision, the inverted and cylindrical cell types share a significant potential for malignant transformation. Although the reported incidence of malignant transformation is widely variable, in our experience about 3-5% of inverted Schneiderian papillomas are associated with a carcinoma. The vast majority of these malignancies are squamous cell carcinomas. For this reason, Schneiderian papillomas should be entirely submitted for histologic evaluation of a carcinomatous component. There are no reliable histologic indicators to indicate those papillomas that are most likely to harbor a carcinoma.