Answer: Cylindrical cell papilloma

Histology: A small biopsy was taken of an intranasal papillary lesion and submitted for frozen section analysis. Even in this small sample, one can discern both endophytic and exophytic growth components. The epithelium is multilayered and composed of cells with abundant pink cytoplasm. At the surface, the cells are ciliated. The epithelium is most striking for the abundant presence of round intraepithelial cysts filled with round pink secretions. These cysts are confined to the epithelium and do not occur in the submucosa.

Discussion: The least common subtype of Schneiderian papilloma is the cylindrical cell papilloma. Architecturally this subtype is quite complex demonstrating papillary fronds and elaborate branching. Its growth usually demonstrates both exophytic and endophytic components. 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. In contrast to rhinosporidia, the cysts of cylindrical cell papilloma are intraepithelial and do not occur in the submucosa.

The cylindrical cell papilloma has a predilection for the maxillary sinus, but often shows contiguous involvement of the lateral nasal wall. Like the inverted type of Schneiderian papilloma, the cylindrical cell papilloma has a marked potential for intramucosal spread. This tendency toward intramucosal spread is also felt to account for the high recurrence rate of these papillomas following surgical excision. Although it has been difficult to define the risk of malignant transformation of the cylindrical cell papilloma, it is probably closely related to the inverted papilloma with a malignant transformation rate of 10% to 13%.