**8. CEUS for solid renal lesions**

For solid renal masses, revealed by mode B ultrasonography, the differentiation between benign and malignant lesions is very important. The most frequent malignant lesion is renal cell carcinoma (RCC). Angiomyolipoma (AML) and oncocytoma are renal benign lesions [19]. The vascular pattern is a major criterion of differentiation and might be done with CEUS. A different vascular behavior of the renal mass compared with the adjacent parenchyma is specific for a tumor lesion and might be suggestive for malignancy [20]. CEUS has a higher accuracy than Doppler technique for renal cancer detection (100% compared to 71%) [21].

Tumor thrombus in the renal vein is a parenchymal structure with similar vascularization as the origin tumor. CEUS identifies the arterial vessels inside this parenchymal structure developed in the renal vein for the identification of the tumor's nature due to the presence of arterial time within the thrombus of the vascular signal (**Figure 6**). However, an emphasis on this character depicted in the renal vein regions of interest requires an experienced operator [11].

**Figure 6.** Malignant thrombus in inferior vena cava. Sagital evaluation of the retroperitoneal space with representation of inferior vena cava and a large parenchymal structure in the vessel. The aspect is typical for a thrombus. In the presence of a kidney tumor, the aspect suggests a vascular invasion.
