The nephroblastomatosis complex and its relationship to Wilms' tumor.

Nephroblastomatosis (NB), a persistence of abnormal embryonal renal tissue beyond 36 weeks' gestation, is often associated with Wilms' tumor. The exact relationship of NB to the development of Wilms' tumor is unclear. Four cases are presented that elucidate the entire morphological spectrum of this disease. Analyses of these cases suggest these conclusions: (1) the NB complex is a spectrum of lesions from benign multifocal nodular renal blastema, resembling residual nephrogenic zones of immature fetal kidney, to Wilms' tumor; (2) infantile NB is a premalignant variant of Wilms' tumor with a favorable outcome usually, when treated early; (3) neonatal nephromegaly requires a complete evaluation and follow-up imaging; persistence mandates biopsy; (4) "second-look" laparotomy is unnecessary with state-of-the-art imaging; and (5) standardization of terminology is essential.