Inverted Urothelial Papilloma : Microscopic Features

On cystoscopy, a typical case of inverted urothelial papilloma (IUP) appears as a small, solitary, slightly raised nodule covered by smooth urothelial mucosa. However, some cases may form an exophytic mass on a stalk, as shown here. Yet, these polypoid masses lack true papillae with fibrovascular cores and show typical anastomosing cords and trabeculae with an endophytic growth pattern. Rare cases of otherwise classic IUP may show rare papillary fronds with true fibrovascular cores. It is acceptable to still call these IUP as long as the true papillary areas are limited to one or two fronds. Rare hybrid cases with areas of classic IUP as well as benign exophytic urothelial papilloma have been documented. These cases warrant follow-up with periodic cystoscopic examination.