Initial imaging. Arteriography Kidney Cross-sectional imaging has replaced arteriography for the evaluation of indeterminate renal masses. There is no relevant literature regarding the use of arteriography in the evaluation of an indeterminate renal mass. Although CT with and without IV contrast is optimal for evaluation of indeterminate renal masses, CT without IV contrast can provide some information. For example, homogenous renal masses measuring <20 HU or >70 HU [1,2] or lesions containing macroscopic fat can be characterized as benign lesions on noncontrast CT. Other studies have also shown that dual-energy CT can differentiate between solid tumors and hyperdense cysts incidentally detected on a single-phase postcontrast CT [13-15] and can be useful when a comprehensive multiphase renal protocol CT is not available. Indeterminate Renal Mass Cystic Renal Masses The Bosniak CT classification system for cystic renal masses encompasses the spectrum from simple renal cyst to cystic RCC, with the likelihood of malignancy increasing with the complexity of the mass [28,29]. Because the presence of any enhancing nodules, walls, or thick septa within a cystic mass is key to determining the probability of malignancy using the Bosniak classification, CT without and with IV contrast is usually necessary for evaluating these lesions. One retrospective study of 156 Bosniak IIF lesions showed that 10.9% of the lesions progressed to malignancy between 6 months and 3.2 years [30]. Another retrospective study of 69 Bosniak IIF lesions and 144 Bosniak III lesions showed malignancy rates of 25% and 54%, respectively [31]. In one study of 312 prospectively classified Bosniak lesions, the malignancy rate at pathology was 38% for Bosniak IIF, 40% for Bosniak III, and 90% for Bosniak IV renal lesions [32]. Oncocytoma is another benign tumor that mimics RCC, and to date there are no specific CT features to reliably differentiate between the two [37].
Indeterminate Renal Mass. Initial imaging. Arteriography Kidney Cross-sectional imaging has replaced arteriography for the evaluation of indeterminate renal masses. There is no relevant literature regarding the use of arteriography in the evaluation of an indeterminate renal mass. Although CT with and without IV contrast is optimal for evaluation of indeterminate renal masses, CT without IV contrast can provide some information. For example, homogenous renal masses measuring <20 HU or >70 HU [1,2] or lesions containing macroscopic fat can be characterized as benign lesions on noncontrast CT. Other studies have also shown that dual-energy CT can differentiate between solid tumors and hyperdense cysts incidentally detected on a single-phase postcontrast CT [13-15] and can be useful when a comprehensive multiphase renal protocol CT is not available. Indeterminate Renal Mass Cystic Renal Masses The Bosniak CT classification system for cystic renal masses encompasses the spectrum from simple renal cyst to cystic RCC, with the likelihood of malignancy increasing with the complexity of the mass [28,29]. Because the presence of any enhancing nodules, walls, or thick septa within a cystic mass is key to determining the probability of malignancy using the Bosniak classification, CT without and with IV contrast is usually necessary for evaluating these lesions. One retrospective study of 156 Bosniak IIF lesions showed that 10.9% of the lesions progressed to malignancy between 6 months and 3.2 years [30]. Another retrospective study of 69 Bosniak IIF lesions and 144 Bosniak III lesions showed malignancy rates of 25% and 54%, respectively [31]. In one study of 312 prospectively classified Bosniak lesions, the malignancy rate at pathology was 38% for Bosniak IIF, 40% for Bosniak III, and 90% for Bosniak IV renal lesions [32]. Oncocytoma is another benign tumor that mimics RCC, and to date there are no specific CT features to reliably differentiate between the two [37].