Radiologic assessment of renal masses: Implications for patient care

THE ability to detect and characterize a mass arising in a kidney has been refined to an unprecedented degree over the past 2 decades due to technologic developments in sonography, computed tomography (CT), and magnetic resonance (MR) imaging (1-9). As these technologies have evolved, the varied imaging characteristics of renal masses have become apparent on the basis of both extensive formal investigations as well as a widely shared clinical experience. Criteria for the radiologic diagnosis of simple and complicated nephrogenic cysts (10-12), abscess (13,14), angiomyolipoma (15-17), hemangioma (18-21), benign and malignant neoplasms (22-39), and inflammatory mass (40) have been thoroughly described. The value of these advances can hardly be disputed. However, it is also clear that their prospective application in a given patient is often subject to uncertainty or associated with wastefulness and futility (1,2,4). For example, the radiologic characteristics of different pathologic entities may overlap. Some features are highly diagnostic of a certain pathologic condition, whereas others are equivocal (11,35,36,41-44). The use of multiple imaging modalities frequently produces data that are either redundant or contradictory. Further, radiologic interpretation is sometimes confounded by small size of the lesion (44,45). In any of these circumstances, the diagnostic radiologic effort may fail to provide data that usefully inform subsequent therapeutic choices and/or patient outcome. Contemporary imaging has also opened a Pandora's box, revealing conditions previously undetectable with imaging. These conditions include the discovery of a small solid mass or a hyperattenuating fluid-filled mass in the kidney of an asymptomatic patient (25,46-64). Many of these small solid masses prove to be cancer at an early stage, and their early detection may account for the much heralded improvement in survival rates for renal cancer recently reported (65-67). The true implications of these apparent salutary effects of CT and sonography, however, are yet to be determined, as emphasized by questions regarding lead time bias of early detection and the biologic activity of incidentally discovered small lesions (68). In this review of the role of the radiologic evaluation of a renal mass in clinical decision making, we use pathologic characteristics as our benchmark. Radiologic data are considered as indirect analogues for these pathologic features. Further, a final tissue diagnosis is considered the province of the pathologist, not the radiologist. In this sense, a proper radiologic diagnosis is viewed as a prediction of a final tissue diagnosis, with an implied level of probability that is based on what is known about the inherent pathologic characteristics of the proposed diagnosis, on the sensitivity of the modality or modalities used, and, to a lesser extent, on the prevalence and demographic features of the diagnoses under consideration.