**7. CEUS in renal pseudo-tumors**

Renal pseudotumors refer to persistent fetal lobulation, dromedary hump, and hypertrophied column of Bertin. These mass-like lesions are frequently detected on conventional ultrasound. The characteristic features are: location between overlapping portions of two renal sinus systems, clear demarcation from the renal sinus, size <3 cm, similar echogenicity to renal parenchyma, and lesions being bordered by a junctional parenchyma line; the Doppler mode demonstrates the regular, branch-like blood flow in the lesion [15].

There are, however, a number of situations in which their diagnosis is difficult—they may be miss-interpreted as kidney tumors through 2D gray scale techniques. This confounding is found in the following circumstances: modified echogenicity compared to the parenchymal environment, infiltrative tumor formations (metastases and lymphomas) [16], abnormal vascular tracts [17], and obese or noncooperative patients (**Figure 3**).

As CEUS is able to depict the microcirculation, this procedure could make the differential diagnosis between a pseudotumor and a solid mass. The vascular pattern of the "pseudotumors" is similar to adjacent parenchyma [18] (**Figures 4** and **5**). The accuracy of CEUS is similar to contrast-enhanced computer tomography (CE-CT) or magnetic resonance imaging (MRI) for the depiction of a normal vascular pattern in a pseudotumor mass [18].

**8. CEUS for solid renal lesions**

**9. Renal cell carcinoma (RCC)**

of a kidney tumor, the aspect suggests a vascular invasion.

necrosis (**Figure 8**) [8].

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].

Harmonic Contrast-Enhanced Ultrasound (CEUS) of Kidney Tumors

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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].

The clear cell renal cell carcinoma (ccRCC) is the most frequent common variant of renal cancer. Histologically is characterized by numerous thin-walled blood vessels with rich blood flow. The frequent morphological features correspond to intratumoral necrosis, hemorrhage, and calcifications [22]. In ultrasound B mode, the small tumors are often hyperechoic, corresponding to the thin-walled blood vessels with rich blood flow and can mimic angiomyolipoma (**Figure 7**) [8]. Larger tumors are hypoechoic and exophytic, with central anechoic

**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

**Figure 3.** (a and b) Pseudotumor of the left kidney. In the middle part of the kidney, there is an area of parenchyma with hypoechoic and heterogeneous pattern suggesting a tumor. The aspect is uncertain and needs additional data especially from the vascular point of view.

**Figure 4.** (a and b) Pseudotumor of the left kidney (same case as previous). Evaluation with microbubbles demonstrates no tumor in the middle of the kidney. This is a proof of how useful can be CEUS in suspicion of tumors of the kidney.

**Figure 5.** (a–c) Pseudotumor of the left kidney. In gray scale ultrasonography (a), there is a suspicion of a tumor in the middle of the organ. In Doppler color mode (b), there is a small vessel in the suspected tumor, insufficient for an accurate diagnosis. In CEUS focused on the middle of the kidney, there is no specific pattern for neoplasia.
