LAUSR

Contrast-enhanced ultrasound (CEUS) markedly improves the diagnostic accuracy of gray-scale (B-mode) US in the detection and evaluation of focal liver lesions. Moreover, this technique has been adopted in many international guidelines as a reliable imaging tool for the diagnostic work-up of patients at high-risk for developing hepatocellular carcinoma (HCC). According to the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) guidelines, updated in 2020, CEUS plays an active role for the characterization of focal liver lesions, being recommended in patients with inconclusive findings at computed tomography (CT) or magnetic resonance imaging (MRI). Indeed, Wu and colleagues, in a recent meta-analysis, found that CEUS showed excellent diagnostic accuracy in differentiating malignant from benign focal liver lesions with a pooled sensitivity of 0.92, specificity of 0.87, and an area under the curve of 0.96. CEUS enables real-time visualization of specific enhancement patterns during all vascular phases (arterial, portal-venous, and late), providing further morphological information in the characterization of liver lesions, including well-differentiated HCC (w-HCC) and hepatocellular adenoma (HCA). HCAs are benign, generally hormone-induced, liver tumors with female predominance even though male predominance has been increasingly reported in Asian men with hepatitis B infection. The differential diagnosis of HCA and HCC is of crucial significance in highrisk situations for choosing the appropriate clinical workup. At CEUS, HCAs typically show arterial hyper-enhancement, with rapid centripetal filling, without a spoke-wheel or peripheral globular enhancement patterns. However, HCCs as well as hyper-enhancing metastases may present similar arterial features. Moreover, up to 30% of HCAs can show mild delayed central washout, making it difficult the differential diagnosis from malignancies. In this issue of the Journal of Clinical Ultrasound, the authors investigated the usefulness of color parametric imaging (CPI) analysis as an adjunct to CEUS to characterize enhancement patterns of HCA and w-HCC. The application of CPI to the dynamic CEUS loops permits the extraction of perfusion parameters such as the arrival times of US contrast agent at different parts of the liver lesion displayed as a color-coded map. Besides, CPI has been previously reported to improve the qualitative assessment of the lesion's dynamic vascular pattern providing a better depiction of the extent and pattern of the vascular supply. Liu et al included in their study 38 liver lesions (from 38 adult patients) who underwent liver gray-scale US, CEUS examination and were diagnosed by biopsy or surgical pathology. CEUS examinations were performed according to the EFSUMB guidelines using SonoVue as contrast agent, and all images were independently reviewed by two readers with different levels of expertise. Finally, CPI analysis of each CEUS examination was elaborated on the offline software loaded in the US scanner. Discriminant features (p < 0.05) were found mainly in CEUS and CPI features. With regard to the CEUS evaluation, the presence of hyperor iso-enhancement in the portal phase was more common in the HCA than w-HCC (p = 0.022). On CPI qualitative assessment, the centripetal arterial enhancement pattern, and the presence of pseudocapsule enhancement were more frequently observed in patients with HCA than in those with w-HCC (p < 0.05). Interestingly, on quantitative CPI analysis comparison, the arrival time of HCA was significantly earlier than that of w-HCC (p = 0.006). Of note, an almost perfect inter-reader agreement was observed for the differentiation of enhancement patterns and pseudocapsule sign using CPI. Although this study provides preliminary data in the field of CPI, it expands the current application of CEUS examination as a complementary problem-solving role for indeterminate focal liver lesions. However, further investigations with a larger sample size and deeply exploring different pathological subtypes of HCA, with correlation to CT/MRI findings, are needed.