Answer: Schneiderian papilloma, cylindrical cell type

Histology: The specimen consists of a polypoid fragment of edematous respiratory mucosa. The normal pseudostratified ciliated columnar epithelium is largely replaced by multilayer columnar cells with tall and pink cytoplasm. This epithelium is most notable for the presence of infiltrating neutrophils with intraepithelial microabscess formations, and intraepithelial microcysts filled with pink globules. This altered epithelium extends deeply into the edematous submucosa as branching tubular structures. There is no evidence of dysplasia or carcinomatous transformation.

Discussion: Papillomas arising from the Schneiderian membrane are known as “Schneiderian papillomas”. The neoplastic nature of these lesions is manifest by:
1) their ability to grow along the mucosal surfaces with contiguous involvement of multiple sinonasal sites,
2) their high recurrence rate following surgical resection,
3) their ability to compress and erode into adjacent anatomic structures if left untreated, and
4) their significant association with malignant transformation.

Based on current understanding of clinical features and morphologic patterns, it is appropriate to subdivide papillomas of the Schneiderian membrane into 3 variants: fungiform papillomas, inverted papillomas, and the cylindrical cell variant of Schneiderian papilloma. The least common of these variants is the cylindrical cell papilloma. Architecturally, it tends to demonstrate architectural complexity including inverted nests, papillary fronds and elaborate branching. At higher power, multilayered columnar cells with striking eosinophilic cytoplasm and round nuclei characterize this subtype. This epithelium contains prominent small mucous-containing cysts, a feature that is frequently mistaken for the cysts seen in rhinosporidia. Unlike rhinosporidia where the cysts occur within the submucosa, the cysts of cylindrical cell papilloma is confined to the epithelium.

The major problems with Schneiderian papillomas are their propensity for recurrence and, in the case of inverting and cylindrical papillomas, malignant transformation. Resections of Schneiderian papillomas should be entirely submitted for histologic evaluation of an associated carcinoma, an association that is noted in 10 to 15% of the inverted papillomas (the malignant transformation rate of cylindrical cell papillomas is probably lower). For inverted papillomas, the vast majority of these associated carcinomas are squamous cell carcinomas – either in the form of an in-situ lesion or as an invasive process. Squamous cell carcinomas and mucoepidermoid carcinomas have been found in association with cylindrical cell papillomas. There are no reliable features that predict which papillomas will give rise to malignant transformation.

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