Patient background **data** extracted from the charts included age, sex, number of kidneys, and estimated glomerular filtration rate. Extracted **data** regarding lesion characteristics included maximum tumor diameter, laterality, tumor location and tumor histology. The tumor location was categorized as follows based on the definition by Gervais et al. [13] : Exophytic tumors were defined as those with a component extending into the perirenal fat but no component extending into the renal sinus fat. Parenchymal tumors were defined as those limited to the confines of the renal parenchyma, without extension into either the perirenal fat or the renal sinus fat. Central tumors were defined as those with extension into the renal sinus fat. Mixed tumors were defined as those that had components extending into both the renal sinus fat and the perirenal fat.