Figure 4b: Cystic renal cell carcinoma in a 69-year-old man. (a) Coronal baseline US image of the right kidney shows a well-defined 5-cm-diameter exophytic complex cystic mass (arrow). A round hyperechoic structure (*) is present in the mass. (b) Coronal contrast-enhanced US image obtained with the contrast-specific mode during the early arterial phase. The cystic mass (arrow) appears almost completely anechoic due to the suppression of fundamental signals by the software. Initial enhancement of hepatic arterial vessels and renal cortical parenchyma is seen. (c) Coronal contrast-enhanced US image obtained with the contrast-specific mode during the nephrographic phase. Enhancement of a solid endocystic nodule (*) with irregular contours is demonstrated. This complex cystic renal mass was classified as a Bosniak IV lesion. (d) Transverse unenhanced CT image of the right kidney shows an exophytic high-attenuation hemorrhagic cyst (*) with a small low-attenuation endocystic component. (e) Transverse contrast-enhanced CT image of the right kidney obtained during the nephrographic phase shows enhancement of an intracystic nodule that became isoattenuated with hemorrhagic fluid (Bosniak category IV lesion). Microscopic examination of the resected specimen (not shown) revealed cystic clear cell carcinoma.