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

Purpose: 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).

Methods: 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: ≤4 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.

Results: 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 (≤7 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).

Conclusions: Tumor size (≤4 or 4-7 cm) and male gender are significant factors associated with compensatory hypertrophy after surgery.