Abstract
Transitional papilloma (inverted papilloma, Schneiderian papilloma) is a relatively common, benign epithelial neoplasm of the sinonasal tract that also occurs in the lacrimal drainage system. The name transitional papilloma is recommended because it reflects the key histological features required for pathological diagnosis, as well as the histogenesis of the tumour. The histogenesis of the tumour is reviewed, together with its natural history, which is characterized by bone remodelling and destruction, a tendency to recur and to undergo malignant transformation. Biomarkers associated with these features have been identified in the sinonasal tumours and may also be of relevance to the lacrimal sac tumours, although the necessary studies have not yet been undertaken.