Changes in Kidney Volume after Robot-Assisted Partial Nephrectomy and Impact on Postoperative Renal Function.

Introduction: The objectives of this study were to measure the changes in kidney volume after robot-assisted partial nephrectomy (RAPN) and examine the impact on the postoperative renal function. Methods: This study included 58 patients undergoing RAPN at our institution between July 2017 and November 2019. Kidney volume was measured with Synapse VINCENTv3.1 (Fujifilm Medical Co., Tokyo, Japan) based on the findings on contrast-enhanced CT before and after RAPN. Results: At 1 week post-RAPN, kidney volumes on the operated side, contralateral side, and overall were significantly larger compared with preoperative measurements (110.6%, p < 0.001; 113.2%, p < 0.001; 112.1%, p < 0.001, respectively). By 1 year postoperation, the operated-side and total kidney volumes had significantly decreased compared with the preoperative levels (83.2%, p < 0.001; 92.7%, p < 0.001), whereas the contralateral kidney volume showed a slight but significant increase (102.1%, p = 0.027). In addition, the estimated glomerular filtration rate (eGFR) decreased by 12.8% at 1 year after RAPN compared with the preoperative value. Multivariate analysis revealed that age, warm ischemia time, and changes in total kidney volume at 1 year had independent impacts on changes in eGFR. Furthermore, only changes in kidney volume on the operated and contralateral sides were shown to be independently associated with changes in total kidney volume 1 year after RAPN. A higher R.E.N.A.L. nephrometry score, L score, and a smaller preoperative total kidney volume were identified as independent predictors of contralateral renal enlargement 1 year after RAPN. Conclusions: This study confirmed the occurrence of compensatory hypertrophy of the contralateral kidney after RAPN. This phenomenon associated with a higher R.E.N.A.L. nephrometry score, L score, and a smaller preoperative total kidney volume.