Benign primary renal masses include simple renal cysts, psuedotumours, angiomyolipomas, oncocytomas, juxtaglomerular tumours, multilocular cystic nephromas, mesoblastic nephromas and papillary adenomas. In a recent surgical series of 228 patients who underwent partial or radical nephrectomy with lesions ≤4 cm, 26.3% were benign [3]. The relatively high percentage of patients with benign renal cortical neoplasms who undergo surgery highlights the importance of new diagnostic technology in avoiding over-treatment.