Differentiation of Exophytic Renal Masses with Determination of the Angular Interface with Renal Parenchyma in US and CT

Purpose: To determine whether benign exophytic renal masses can be distinguished from malignant lesions by using the angular interface sign in ultrasonography (US) and computerized tomography (CT). Materials and Methods: A total of 71 cases with exophytic renal mass (2 cm or greater) were examined on the basis of angular interface in US (n = 23), CT (n = 21) and US + CT (n = 16) between January 2008 and June 2010 were included in this study. The renal interface relationships were examined by 2 radiologists and classified as having angular or wide interface. Results: No statistically significant difference was found between the findings of two readers. There was almost perfect interobserver agreement for the interface sign. For cystic lesions, the angular interface sign was determined in all but two Bosniak category 1 cases. Also, the angular interface sign was positive in all but one Bosniak category 2 - 3. For cystic lesions with solid component and pure solid lesions, in the benign group, the angular interface sign was positive in all except three cases (vascular malformation, oncocytoma and Xanthogranulomatous pyelonephritis). In the malignant group, the angular interface sign was determined in only two RCC cases; in other primary or metastatic malignant lesions there was a wide interface sign. Conclusion: Exophytic renal masses can be differentiated as malignant or benign with 87% accuracy using only the angular interface sign in US or CT and also in opposition to dynamic-contrast examinations. This method entails a lack of additional radiation or contrast media exposure, time-saving, and costeffectivity.