Qualitative and quantitative characteristics of CEUS for renal cell carcinoma and angiomyolipoma: a narrative review

Abstract

Incidental findings of renal masses are increasing. However, a substantial portion of surgically treated renal masses turn out to be benign on histopathological examination. Thus, there is a clear need for improved pre-surgical assessment to minimize unnecessary invasive procedures. The challenge intensifies when distinguishing between renal cell carcinoma (RCC) and angiomyolipoma (AML) in renal lesions smaller than 4 cm with minimal adipose tissue. In such cases, contrast-enhanced ultrasound (CEUS) has emerged as a valuable diagnostic tool, by utilizing both qualitative and quantitative parameters. Quantitative measures offer objectivity, reliability, and reproducibility compared to qualitative parameters, enabling the characterization of RCC subtypes and differentiation from AML. Qualitative features as enhancement pattern, degree, and peak were less helpful in distinguishing triphasic minimal fat AML (TAML) from epithelioid AML (EAML), with the pseudocapsule sign potentially being the only distinguishing qualitative feature. The pseudocapsule sign was more frequently observed in ccRCCs (38.0%) than in AMLs (15.6%). Moreover, it was detected in 40.0% of EAMLs and 34.5% of ccRCCs but not in TAMLs due to similar growth patterns between EAMLs and low-grade ccRCCs. Quantitative measures such as the time-to-peak (TTP) ratio can further enhance diagnostic accuracy and also TOC ratio should be considered, as it was higher in clear cell RCCs (ccRCCs) and in EAMLs compared to TAMLs, indicating behavior similar to ccRCCs. However, CEUS remains an operator-dependent exam.

Contrast-Enhanced Ultrasound in the Diagnosis of Solid Renal Lesions

“…The results of studies conducted in the recent past have confirmed that the presence of a pseudo-capsule, rapid wash-out, and high and heterogeneous enhancement on CEUS examination indicate the malignant nature of the lesion and most often indicate a diagnosis of renal cell carcinoma [19,22,24]. In contrast, benign lesions usually show slow centripetal enhancement, homogeneous peak enhancement, and gradual wash-out [19,24].…”

“…The most common benign solid tumors of the kidney are AML and renal oncocytoma [18]. AMLs are hamartomatous benign tumors composed of newly formed vessels, smooth muscle cells, and well-differentiated adipose tissue [19]. About 80% of AMLs occur as isolated entities, but they can also be associated with the tuberous sclerosis complex [20].…”

“…Malignant lesions on CEUS examination are most often characterized by heterogeneous enhancement, rapid wash-out, and the presence of a pseudo-capsule sign (Figure 1). By contrast, benign lesions usually show slow centripetal enhancement, homogeneous peak enhancement, and gradual wash-out [19]. Taking into account the different histotypes of both benign and malignant lesions, a typical picture can be presented on CEUS examination.…”

Contrast-enhanced ultrasound for differentiating benign from malignant focal solid renal lesions in pediatric patients

“…CEUS is a useful method to visualize the contrast enhancement features of RCC subtypes in adults 23 , 24 . Clear cell RCCs show typical hyperenhancement with wash-out, while papillary RCCs and chromophobic RCCs show hypoenhancement throughout the enhancement phases 10 , 25 .…”