A useful method for assessing differences of compensatory hypertrophy in the contralateral kidney before and after radical nephrectomy in patients with renal cell carcinoma: ellipsoid formula on computed tomography.

Objective: To investigate the usefulness of the ellipsoid formula for assessing compensatory hypertrophy of the contralateral kidney on pre-operative and post-operative CT in renal cell carcinoma (RCC) patients. Methods: We retrospectively identified 389 patients who had radical nephrectomy for RCC between 2011 and 2015. Contrast-enhanced CT was performed within 3 months pre-operative and at 1 year post-operative. The kidney volumes were calculated from CT using the ellipsoid formula. We subdivided patients into three groups based on tumour size (I: <= 4 cm, II: 4-7 cm, III: > 7 cm). Volumetric renal parameters were compared and multivariate analyses were performed to determine predictors associated with pre-operative and post-operative compensatory hypertrophy. Results: Kidney volume calculation using the ellipsoid method took a median of 51 s. Group III had a significantly larger median pre-operative contralateral renal volume than Groups I and II (I: 140.4, II: 141.6, III: 166.7 ml, p < 0.05). However, the median ratio of post-operative contralateral renal volume change was significantly higher in Groups I and II than Group III (I: 0.36, II: 0.23, III: 0.12, p < 0.001). On multivariate analysis, tumour size revealed the strongest positive association with pre-operative contralateral kidney volume (partial regression coefficient: beta = 30.8, > 7 cm) and ratio of post-operative contralateral kidney volume change (beta = 0.214, I vs III; beta = 0.168, II vs III). Conclusion: Kidney volume calculation for assessing pre- and post-operative compensatory hypertrophy of the contralateral kidney in RCC patients can be easily and rapidly performed from CT images using the ellipsoid formula.