Pitfalls in renal mass evaluation and how to avoid them.

Characterization of renal masses with computed tomography (CT) and magnetic resonance (MR) imaging is usually clear-cut and accurate. However, potential pitfalls exist in diagnosis of renal masses, and it is necessary to understand these pitfalls to avoid misdiagnosis and possibly unnecessary surgery. Although some of the pitfalls are related to technical factors of the CT and MR imaging equipment, others are related to errors in image interpretation. To maximize detection and characterization of renal masses, the study should include images obtained before and after administration of intravenous contrast material, including images obtained during the nephrographic phase of enhancement. One should be aware of the potential unreliability of absolute Hounsfield unit measurements and of the existence of possible CT pseudoenhancement. When CT results are indeterminate, MR imaging may be helpful in demonstrating enhancement in renal masses. Before diagnosing a renal mass as a malignant neoplasm or suggesting surgery for a renal mass, one should consider alternative benign diagnoses; when appropriate, previous images or a supporting history should be obtained.