Pseudocarcinomatous hyperplasia of the urinary bladder.

We review the morphology and differential diagnoses of pseudocarcinomatous hyperplasia of the bladder, using a study case to illustrate the discussion. Pseudocarcinomatous hyperplasia is a rare, reactive response to an ischemic insult, classically to radiation therapy, and consists of proliferative, pseudoinfiltrative urothelial nests within the stroma. The presence of background radiation therapy-related changes, such as numerous dilated thrombosed vessels, reactive-appearing endothelial and stromal cells, edema, and hemorrhage, can provide clues to the diagnosis. The main differential diagnoses include invasive urothelial carcinoma and the nested variant of urothelial carcinoma; morphologic features, such as the presence or absence of background therapy-related changes and the architecture and the cytologic atypia of the nests, can help distinguish between pseudocarcinomatous hyperplasia and urothelial carcinoma.