Differentiation of Renal Tumor Histotypes: Usefulness of Quantitative Analysis of Contrast-Enhanced Ultrasound

The purpose of this study is to evaluate quantitative analysis of contrast-enhanced ultrasound (CEUS) in the differential diagnosis of renal tumor histotypes. Between January 2010 and December 2013, 106 clear cell renal cell carcinomas (RCCs) (mean [± SD] diameter, 3.7 ± 1.8 cm), 34 angiomyolipomas (mean diameter, 4.1 ± 1.4 cm), 25 papillary RCCs (mean diameter, 3.5 ± 1.1 cm), and 28 chromophobe RCCs (mean diameter, 2.9 ± 0.9 cm) underwent CEUS quantitative analysis. The dynamic vascular pattern was analyzed with the Fisher exact chi-square test, and rise time, time to peak (TTP), and tumor-to-cortex enhancement ratio were analyzed with the independent-sample t test. Dynamic vascular pattern types I and III (hyperenhancement) were more common among clear cell RCCs, whereas type II (hypoenhancement) was more common among angiomyolipomas, papillary RCCs, and chromophobe RCCs. Irrespective of dynamic vascular pattern class, the rise time and TTP were the shortest in clear cell RCCs and were equal in angiomyolipomas, papillary, and chromophobe RCCs. The tumor-to-cortex enhancement ratio was the highest in clear cell RCCs, was second highest in angiomyolipomas, and was lowest but equal in papillary and chromophobe RCCs. Clear cell RCCs and angiomyolipomas accounted for the majority of the hyperenhancing group. The tumor-to-cortex enhancement ratio of clear cell RCCs was higher than that of angiomyolipomas. With tumor-to-cortex enhancement ratio greater than 146.0% as the cutoff to differentiate clear cell RCC from angiomyolipoma in the hyperenhanced group, the sensitivity and specificity were each 71.4%. In the hypoenhanced group, the tumor-to-cortex enhancement ratio was the same in clear cell RCCs and angiomyolipomas but was higher in papillary and chromophobe RCCs. With tumor-to-cortex enhancement ratio greater than 54.2% as the cutoff point to differentiate clear cell RCCs from papillary and chromophobe RCCs, the sensitivity and specificity were 95.5% and 94.8%, respectively, whereas with a tumor-to-cortex enhancement ratio greater than 57.4% as the cutoff point to differentiate angiomyolipomas from papillary and chromophobe RCCs, the sensitivity and specificity were 90.0% and 96.4%, respectively. Quantitative analysis of CEUS can show quantification of enhancement features of different renal tumor histotypes and may be helpful in their differential diagnosis.