Course Map: Epithelial Tumors: Benign: Urothelial Papilloma, Inverted Type

Urothelial Papilloma, Inverted Type
As with the papilloma, the cells are not atypical but the growth is endophytic rather than exophytic. They are solitary lesions, usually on a pedicle (Figure 1), and most of them occur in the bladder neck or trigone. The surface epithelium is smooth and histologically normal or slightly thinned. Invaginations from the surface extend into the stroma to form a maze-like proliferation of anastomosing cords of urothelium. Figure 2, Figure 3, and Figure 4 show three different examples of inverted papilloma to illustrate their repetitive morphology, and Figure 5 is a high magnification showing the typical cellular features. In the center of many cores some epithelial cells are spindled. Mitoses are rare and usually absent. As described above, these have no malignant potential [24].
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	Figure 1: Inverted papilloma on a pedicle.
	Figure 2: Inverted papilloma.
	Figure 3: Inverted papilloma.
	Figure 4: Inverted papilloma.
	Figure 5: Note orientation of epithelial cells. In the center of many cores, the cells tend to be elongated (arrows A). Otherwise, the cells are oriented at right angles to the core (arrows B).