The urothelial nuclei are enlarged and hyperchromatic and there is architectural disorganization. Nuclear chromatin is smudged. Mitotic activity is not increased. Atypical nuclei of radiation cystitis have more bizarre shapes than those seen in carcinoma-in-situ. In some cases, however, the distinction between the two may be extremely difficult. Urothelial atypia may last for years after the last radiation dose.