Renal Masses: Evaluation with Contrast-Enhanced Ultrasound, with a Special Focus on the Pseudocapsule Sign

The aim of this study was to analyze the diagnostic performance of contrast-enhanced ultrasound (CEUS) in differentiating between benign and malignant renal masses, with a special emphasis on the value of the pseudocapsule sign. A total of 163 consecutive patients with 163 renal masses were involved. The conventional ultrasonography and CEUS features were assessed. Sensitivity, specificity and the area under the receiver operating characteristic curve (Az) were calculated for qualitative CEUS, and a multivariate analysis was performed to analyze the correlation between the sonographic features and malignancy. Time to peak (TTP) and peak intensity (PI) were compared between benign and malignant renal masses for quantitative CEUS analysis in 72 of 163 patients. Intraclass correlations were calculated for variability in intensity and time parameters between qualitative and quantitative evaluation. Among all qualitative CEUS features, the pseudocapsule sign showed the highest Az (0.777; 95% confidence interval: 0.701-0.853) and yielded the highest sensitivity (67.4%) and specificity (88.0%); multivariate logistic regression analysis showed that the pseudocapsule sign and color Doppler flow imaging patterns were the two strongest independent predictors for malignancy. For quantitative CEUS analysis, higher PI and shorter TTP were found in malignant renal masses than those in benign ones. The Intraclass correlation coefficient values among qualitative and the quantitative assessments were 0.00 for time and 0.03 for intensity. The pseudocapsule sign offered the most efficient performance among all the qualitative and quantitative CEUS features.