Neoplastic surface changes in urothelium of rats after portacaval anastomosis. A combined light and scanning electron microscopic study.

The development of preneoplastic and neoplastic alterations in the urinary tract was investigated by light and scanning electron microscopy in rats after portacaval anastomosis. The changes consisted of slight hyperplasia to papillary hyperplasia after 24 weeks. Carcinomas were present in all animals after 52 weeks. Surface characteristics can be correlated with the sequence of changes in urothelial cells. Short uniform microvilli appear in moderate hyperplasia and a cobblestone formation of the cells is typical of papillary hyperplasia. In transitional cell carcinomas the cells varied in shape and size and they were densely covered with pleomorphic microvilli. Although the cause of tumour induction after portacaval anastomosis is not clearly understood, possible mechanisms are discussed.