Purpose: The purpose of this study is to evaluate qualitative and quantitative analysis of contrast-enhanced ultrasound (CEUS) in differential diagnoses of hypo-echoic renal tumor histotypes.
Methods: Our study cohort comprised 103 clear cell renal cell carcinomas (ccRCCs), 24 papillary renal cell carcinomas (pRCCs), 28 chromophobe renal cell carcinomas (cRCCs), and 34 angiomyolipomas (AMLs), hypo-echoic on ultrasound, and imaged between January 2011 and December 2013. Enhancement homogeneity and tumor-to-cortex intensity ratio (TOC ratio) were retrospectively analyzed.
Results: Overall, heterogeneous enhancement was more common in ccRCCs than AMLs, pRCCs, and cRCCs. TOC ratio showed the trend ccRCC > AML > pRCC = cRCC. Similar trends were seen in tumors <4 cm. Using heterogeneous enhancement or TOC ratio >107.5% to differentiate ccRCC from other histotypes, the sensitivity, specificity, positive and negative predictive values were 93.1%, 74.5%, 84.8%, and 87.5%, respectively. Tumors >4 cm exhibited considerable overlap in enhancement homogeneity among different histotypes. TOC ratios were similar between homo- and heterogeneously enhancing tumors for ccRCCs and for pRCCs and cRCCs, but higher in homogeneously enhancing than heterogeneously enhancing AMLs. In homo- and heterogeneously enhancing tumors, TOC ratios followed the trends ccRCCs > AMLs > pRCCs = cRCCs and ccRCCs > AMLs = pRCCs = cRCCs, respectively. With TOC ratio >105.81% and >72.37% to differentiate homo- and heterogeneously enhancing ccRCCs from other histotypes in tumors >4 cm with same enhancement homogeneity, the sensitivity, specificity, positive and negative predictive values were 70.0%, 85.7%, 70.0%, 85.7%, and 91.7%, 94.4%, 95.7%, 89.5%, respectively.
Conclusion: CEUS homogeneity and TOC ratio are helpful in differential diagnosis of hypo-echoic renal tumor histotypes. Diameter and enhancement homogeneity should be considered when deciding the diagnostic TOC ratio cutoff.