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 tu bulo-papillary adenoma (so-called nephrogenic adenoma) arising in the renal Pelvis of a 35-year-old woman. The tumor showed a polypoid exoph ytic growth and consisted of closely packed tubular formations lined b y cuboidal to low columnar cells with an admixture of delicate papilla ry 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-p apillary adenoma'' seems more appropriate than the designation ''nephr ogenic adenoma''. True tumors of this type should clearly be distingui shed from metaplastic tubular, papillary or tubulo-papillary cuboidal hyperplasias of the urothelium (so-called nephrogenic metaplasia) whic h are considered preneoplastic and assumed to be immediate precursors of adenomas of the lower urinary tract.