Benign Urothelium : Brunn Nests
Brunn nests represent a commonly encountered reactive change and consist of solid nests of urothelial cells within the lamina propria. Some nests may retain connection with the overlying urothelium, where as others appear free in the lamina propria. The most important differential diagnosis is with nested variant of urothelial carcinoma. Brunn nests are usually large, superficially located, regular in shape and spacing, and lack cytologic atypia.