Tubulo-papillary adenoma (so-called nephrogenic adenoma) arising in the renal pelvis. Report of a case with a critical consideration of histogenesis and terminology.

This is the first detailed clinical and histopathologic report of a tubulo-papillary adenoma (so-called nephrogenic adenoma) arising in the renal pelvis of a 35-year-old woman. The tumor showed a polypoid exophytic growth and consisted of closely packed tubular formations lined by cuboidal to low columnar cells with an admixture of delicate papillary structures. Its benign nature was indicated by the lack of cellular atypias, the extremely low proliferative activity and the absence of invasiveness. We favor the metaplastic theory of origin rather than an embryologic (dysontogenetic) derivation from mesonephric remnants as the underlying histogenetic principle. The descriptive term "tubulo-papillary adenoma" seems more appropriate than the designation "nephrogenic adenoma". True tumors of this type should clearly be distinguished from metaplastic tubular, papillary or tubulo-papillary cuboidal hyperplasias of the urothelium (so-called nephrogenic metaplasia) which are considered preneoplastic and assumed to be immediate precursors of adenomas of the lower urinary tract.