Pathological Insights into Non-Neoplastic Renal Parenchyma in Wilms Tumor: Implications for Nephron-Sparing Surgery.

Introduction:  This study aimed to evaluate the non-neoplastic renal parenchyma in Wilms tumor (WT) and investigate its impact on nephron-sparing surgery (NSS).

Materials and methods:  The non-neoplastic renal parenchyma of WT patients was prospectively collected for pathological examination. The histology of non-neoplastic renal parenchyma was assessed from two perspectives: nephrogenic rests (NRs) and nephrons.

Results:  A total of 46 non-neoplastic renal parenchyma specimens were collected from 42 WT patients. The surgeons assessed the median proportion of non-neoplastic renal parenchyma as 30%, whereas using ellipsoid volume, it was calculated to be 27%. The Youden index of surgeons' assessment peaked at a 15% proportion of non-neoplastic renal parenchyma. The bilateral WT (BWT) group and NSS group exhibited significant differences compared with the unilateral WT group and radical nephrectomy group, respectively, with the BWT group showing a tendency toward thickened basement membrane.

Conclusion:  The presence of NRs and endogenous nephron alternations should be given due attention in WT. The probability of abnormalities is low when the proportion of non-neoplastic renal parenchyma exceeds 15%, providing pathological support for expanding the adaptation of NSS.