This Journal feature begins with a case vignette highlighting a common clinical problem. Evidence supporting various strategies is then presented, followed by a review of formal guidelines, when they exist. The article ends with the authors' clinical recommendations.
A 65-year-old man with a history of well-controlled hypertension presents for a follow-up visit after an incidental finding of a small mass in the right kidney on an abdominal computed tomographic (CT) scan. (The scan had been ordered to evaluate pain in the lower quadrant, which resolved.) The mass is 3.2 cm in its largest dimension, anterior, heterogeneous, and solid, and it is in the right renal hilum near the main renal artery, vein, and ureter; the left kidney appears normal. The patient feels well, and his physical examination is unremarkable. His serum creatinine level is 1.2 mg per deciliter (106 μmol per liter). How should this patient be further evaluated and treated?
THE CLINICAL PROBLEM
One result of the widespread use of advanced cross-sectional imaging is that small, incidental renal masses have become common radiologic findings. Approximately 13 to 27% of abdominal imaging studies incidentally identify a renal lesion.1,2 The majority of these lesions are small, simple cysts that do not show enhancement after the administration of contrast material, are benign, and require no treatment. A minority of small renal masses are solid masses or complex cystic masses, show contrast enhancement on CT images, and are suggestive of cancer. An enhancing mass is a mass that is seen on CT to have an increase in density of more than 15 Hounsfield units after the administration of contrast material.3
For the purposes of this article, a small renal mass is defined as a contrast-enhancing mass with a largest dimension of 4 cm or less on abdominal imaging.4 From 1988 to 2003, the incidence of small renal masses increased relative to other renal tumors, and they now make up 48 to 66% of all renal tumors that are diagnosed and 38% of all renal tumors that are excised5,6; often the patient has had no symptoms. Of small renal masses, approximately 80% are malignant and 20% are benign. 7 When a small renal mass is identified incidentally on imaging, the clinical-management challenge involves distinguishing benign masses from those likely to be malignant and determining the appropriate treatment of malignant masses.