Tumor size is associated with compensatory hypertrophy in the contralateral kidney after radical nephrectomy in patients with renal cell carcinoma

To assess the association between tumor size and postoperative compensatory hypertrophy of the contralateral kidney estimated with preoperative and postoperative CT in patients with renal cell carcinoma (RCC). We prospectively identified 728 patients who underwent radical nephrectomy for RCC between 2012 and 2014. Contrast-enhanced CT was done within 3 months preoperatively and 1 year postoperatively. A tissue segmentation tool program with CT images was used to estimate kidney volume. We divided patients into three groups according to tumor size (A: a parts per thousand currency sign4 cm, B: 4-7 cm, C: > 7 cm). Preoperative and postoperative volumetric kidney parameters were compared and multivariable linear regression model was used to analyze predictors associated with postoperative compensatory hypertrophy. The preoperative median contralateral kidney volume was significantly larger in group C than in groups A and B (A: 170.3, B: 176.9, C: 186.8 mL, p < 0.05); the median tumor-side renal parenchymal volume was smaller in group C than in the other groups (A: 168.4, B: 171.1, C: 139.0 mL, p < 0.001). However, the postoperative median contralateral kidney volume among the three groups was not significantly different; the median contralateral kidney volume change after surgery was significantly larger in groups A and B than in group C (A: 37.8, B: 37.5, C: 27.4 mL, p < 0.05). Tumor size (a parts per thousand currency sign7 cm) (p = 0.001) and male gender (p < 0.001) were significantly correlated with increased contralateral kidney volume on multivariable analysis. Tumor size showed the strongest positive association with postoperative contralateral kidney volume (A vs. C, partial regression coefficient = 10.6; B vs. C, partial regression coefficient = 10.5). Tumor size (a parts per thousand currency sign4 or 4-7 cm) and male gender are significant factors associated with compensatory hypertrophy after surgery.