Inverted Urothelial Papilloma : Microscopic Features

Comments:
Microscopic Features: Inverted urothelial papilloma shows inverted (endophytic) growth pattern and a trabecular architecture in a typical case. Exophytic papillary structures are absent or minimal. Urothelial cells form branching and anastomosing cords and trabeculae of relatively uniform width that arise from the overlying smooth-surfaced urothelium and proliferate in the lamina propria. Muscularis propria is not involved. The trabeculae are usually 5-10 layers thick and show basophilic, palisaded basal cells on the outside and maturing urothelial cells on the inside due to the inverted growth pattern. There is scant intervening stroma composed of loose fibrovascular tissue without inflammation.