Primary extrarenal Wilms'' tumour: identification of a putative precursor lesion

We report a case of primary extrarenal Wilms' tumour which, on histological examination, revealed a zone of hyalinized blastema adjacent to, and within the tumour capsule. The tumour showed a predominant stromal component. The presence of the hyalinized blastema adjacent to the tumour raises the possibility that some cases of extrarenal Wilms' tumour may have a precursor lesion.