Ultrasound CEUS Characteristics for Renal Cell Carcinoma vs. Angiomyolipoma: A Narrative Review

The rise in incidental findings of renal masses through imaging highlights the importance of accurate pre-surgical evaluations, as many masses found to be benign on histopathology often lead to unnecessary surgeries. Differentiating between renal cell carcinoma (RCC) and angiomyolipoma (AML) is especially challenging for small renal lesions (under 4 cm) with minimal fat content. In this context, contrast-enhanced ultrasound (CEUS) has become a valuable diagnostic tool, using both qualitative and quantitative parameters to improve assessment accuracy. Qualitative CEUS features, such as enhancement patterns and the pseudocapsule sign, are particularly effective in distinguishing RCC, especially clear cell RCC (ccRCC), from AML. The pseudocapsule sign, an enhanced border seen on CEUS, is more prevalent in RCCs than AMLs, appearing in 38% of ccRCC cases and only 15.6% of AML cases. Quantitative measures, like the time-to-peak (TTP) ratio and the tumor-to-cortex (TOC) enhancement ratio, also enhance diagnostic accuracy. TOC ratios are notably higher in ccRCCs and epithelioid AMLs (EAMLs) than in triphasic minimal fat AMLs (TAMLs), helping to differentiate the benign TAML from the malignant-prone EAML. CEUS offers additional benefits, as it is radiation-free and safe for patients with renal impairment or metal implants, providing real-time imaging that reduces reliance on more invasive techniques. Nevertheless, CEUS remains dependent on the operator’s expertise and, although effective, it is often used in conjunction with CT and MRI for comprehensive evaluations. With continued advancements in CEUS technology and increasing expertise, CEUS is positioned to become a highly reliable tool for characterizing renal lesions, offering significant potential for accurate, minimally invasive renal mass assessments.