To determine the incidence of benign pathologic findings at partial nephrectomy for a solitary renal lesion when preoperative imaging is reviewed by an experienced team of academic genitourinary radiologists.

From 1996 to 2004, 143 patients underwent resection of a solitary renal lesion for presumed renal cell carcinoma amenable to partial nephrectomy. Our experienced team of genitourinary radiologists interpreted all preoperative imaging scans. Of the 143 patients, 44 underwent partial nephrectomy for a solitary lesion less than 2 cm, 85 for a lesion 2 to 4 cm, and 14 for a lesion greater than 4 cm.

Of the 143 solitary masses resected, 23 revealed benign pathologic findings (16.1%). Ten lesions (43.5%) were angiomyolipomas (AMLs), eight (34.8%) were oncocytomas, three (13.0%) were benign Bosniak-type cysts, and one each was a low-grade spindle cell lesion most consistent with mesoblastic nephroma, and a metanephric adenoma.

A significant fraction of small solitary renal masses presumed to be renal cell carcinoma had benign pathologic findings on resection, despite thorough expert radiologic review. Management should favor parenchyma-sparing approaches, because resection serves not only a therapeutic but also a diagnostic function. Patients should be counseled accordingly when faced with the diagnosis of renal mass.