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

**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

**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 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.

124 Evolving Trends in Kidney Cancer

diagnosis. In CEUS focused on the middle of the kidney, there is no specific pattern for neoplasia.

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

The papillary renal cell carcinoma are described in B mode ultrasound as unilocular and hypoechoic. The CEUS features of this type of RCC are: hypoenhance to renal parenchyma

Harmonic Contrast-Enhanced Ultrasound (CEUS) of Kidney Tumors

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Typically, AMLs contain macroscopic fat and in B mode ultrasound, there are homogeneously echogenic. There are lipid-poor AMLs that correspond to isoechoic feature on B mode ultrasound. The CEUS reveals for AMLs the following vascular pattern: homogeneous, hypoenhanced compared to adjacent renal parenchyma (**Figure 9**). The contrast agent persists in delayed phases. This characteristic is very important in differential algorithm for RCC [8].

Oncocytoma are considered benign lesions. In B mode ultrasound, a hypoechoic central scar might be present, and color Doppler might show central radiating vessels (**Figure 10**) [8]. The differential diagnosis with chromophobe RCC of low malignant potential might be difficult. The vascular pattern depicted on CEUS was described differently in published case reports. It was documented a spoke wheel configuration of vessels on CEUS in an oncocytoma [20]. But other authors depicted an enhancement from periphery to center [8, 23]. The majority of the reports found hyperenhancement early compared with normal renal parenchyma and persis-

**Figure 9.** (a and b) Angiomyolipoma. CEUS (left) and gray scale ultrasonography (right). There is a tumor, round, well defined, and hypoechoic, with peripheral vascularity. The aspect suggests the presence of a neoplasia, but is not entirely

throughout examination and homogeneous [8].

**10. Angiomyolipoma**

**11. Oncocytoma**

typical for angiomyolipoma.

tent (greater delayed) compared to ccRCC [8, 23].

**Figure 7.** Renal cell carcinoma. Gray scale ultrasonography of the right kidney. At the upper pole, there is a hypoechoic tumor, relatively well defined.

**Figure 8.** Renal cell carcinoma. Gray scale ultrasonography of the right kidney. At the lower pole, there is a round, well defined parenchymal tumor. The aspect is typical for a renal cell carcinoma.

The accuracy of CEUS to predict malignancy was intensively studied, but the results were not similar among authors. These confounding results are due in part to different terminology regarding the arterial and delayed phases, in part due to different contrast agents, and in part due to different features corresponding to natural development of the tumor (different CEUS characteristics depending on size) [8]. Reviewing the literature, ccRCC shows on CEUS the following vascular pattern: early hyperenhancement compared no normal adjacent parenchyma, wash-out on delayed phase, and perilesional enhancement, rim-like, corresponding to a pseudocapsule. There is also a heterogeneous enhancement, which increases with the lesion size [8].

A meta-analysis studied 11 comparable studies (including 567 malignant lesions and 313 benign lesions) and found a sensitivity of 88% and a specificity of 80% for CEUS to differentiate between malignant and benign renal tumors [23].

The papillary renal cell carcinoma are described in B mode ultrasound as unilocular and hypoechoic. The CEUS features of this type of RCC are: hypoenhance to renal parenchyma throughout examination and homogeneous [8].
