Triphasic and epithelioid minimal fat renal angiomyolipoma and clear cell renal cell carcinoma: qualitative and quantitative CEUS characteristics and distinguishing features

Purpose: To determine the contrast-enhanced ultrasonography (CEUS) characteristics of minimal fat renal angiomyolipoma (AML) (triphasic and epithelioid) and compare them to each other and to clear cell renal cell carcinoma (ccRCC) to explore their differential diagnostic clue. Methods: Qualitative and quantitative CEUS analyses were retrospectively conducted for epithelioid renal AMLs (EAMLs) (n = 15), triphasic minimal fat AMLs (TAMLs) (n = 25), and ccRCCs (n = 113). Enhancement patterns and features with CEUS were qualitatively evaluated. As for the quantitative parameters, rise times (RT), time to peak (TTP), and tumor-to-cortex enhancement ratio (TOC ratio) were compared among these renal tumor histotypes. Results: No significant differences were detected on conventional ultrasound in the three histotypes of renal tumor. On qualitative CEUS analysis, centripetal enhancement in cortical phase (73.3% in EAMLs, 84.0% in TAMLs vs. 18.6% in ccRCCs, p < 0.001 for both), homogeneous peak enhancement (100.0% in both EAMLs and TAMLs vs. 43.4% in ccRCCs, p < 0.001 for both), and iso-enhancement in parenchyma phase (53.3% in AMLs, 52.0% in TAMLs vs. 26.5% in ccRCCs, p = 0.034 and 0.013, respectively) were valuable traits for differentiating EAMLs and TAMLs from ccRCCs. Furthermore, with quantitative analysis, RT and TTP were much shorter in ccRCCs than those in EAMLs and TAMLs. However, all these qualitative and quantitative characteristics made no significant difference between EAMLs and TAMLs. In the differential diagnosis of EAMLs from TAMLs, pseudocapsule sign was valuable (40.0% in EAMLs vs. 0.0% in TAMLs, p < 0.001), and TOC ratio was much higher in EAMLs (166.01 +/- 64.47%) than that in TAMLs (93.74 +/- 46.56%)(p < 0.001), though they did make overlaps with ccRCCs. With either heterogeneous peak enhancement or the presence of pseudocapsule or TOC ratio > 97.34% as the criteria to differentiate ccRCCs and EAMLs from TAMLs, the sensitivity and specificity were 80.0% and 87.5%, respectively. Conclusions: Qualitative and quantitative CEUS analyses are helpful in the differential diagnosis of ccRCCs, EAMLs, and TAMLs.