A new precursor lesion of Wilms' tumour (nephroblastoma): intralobar multifocal nephroblastomatosis.

Almost half of the kidneys containing Wilms' tumours also contain persistent renal blastema in one or more of its forms. Persistent renal blastema is present in almost all cases of bilateral nephroblastoma. Multifocal superficial nephroblastemomatosis is the best known form of persistent renal blastema, and there is good evidence that it is a precursor of nephroblastoma. This paper reports four cases of a second, deep cortical type of nephroblastomatosis. This type of persistent renal blastema appears to be a precursor of a distinct histologic subtype of nephroblastoma, and differs from multifocal superficial nephroblastomatosis also in its teratological background.