**11. Oncocytoma**

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 differenti-

**Figure 8.** Renal cell carcinoma. Gray scale ultrasonography of the right kidney. At the lower pole, there is a round, well

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

ate between malignant and benign renal tumors [23].

defined parenchymal tumor. The aspect is typical for a renal cell carcinoma.

tumor, relatively well defined.

126 Evolving Trends in Kidney Cancer

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

Few case reports depicted CEUS vascular pattern of renal metastasis, which are hypovascular on all phases [8]. Renal lymphoma was also described as hypovascular throughout renal per-

Harmonic Contrast-Enhanced Ultrasound (CEUS) of Kidney Tumors

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At imaging studies, approximately 10% of kidney cancers have a complex cystic appearance. Nonmalignant renal tumors may also have a complex appearance. This is most commonly due to the hemorrhage, infection, inflammation or ischemia. Differentiation between complex cysts requiring surgical treatment or monitoring is essential. The identification of vascularity in the solid area or septa of cystic lesions by CEUS simplifies the diagnosis of lesions with

The Bosniak classification differentiates five categories of renal cysts named I, II, IIf, III, and IV based on the imaging criteria (ultrasound and CT), being used for further clinical manage-

First Bosniak category, called I, depicts thin walls of the cyst, without septa and sharp margins. There are no solid components or calcifications. No enhancement is depicted on CEUS. There

**Figure 12.** (a and b) Renal cyst. CEUS evaluation (a); an gray scale evaluation (b). In CEUS (asterisc), the lack of vascular

signal suggests an avascular lesion compatible with the diagnosis of cyst.

fusion after contrast agent administration on ultrasound (**Figure 11**) [8].

**13. Cystic renal lesions**

high malignancy potential [24].

is no malignancy potential (**Figure 12**) [8, 25].

ment of the patient [8, 25].

**Figure 10.** Oncocytoma. Round, parenchymal mass with enhancement of the peripheral vascular bed in the arterial time (Section 22).
