Small (≤ 3 cm) hyperechoic renal masses are challenging to characterize due to overlapping features between angiomyolipomas (AMLs) and renal cell carcinomas (RCCs). Contrast-enhanced ultrasound (CEUS) offers a noninvasive alternative, particularly when CT or MRI are inconclusive or contraindicated. This study assessed CEUS diagnostic accuracy in differentiating RCC from AML and identified predictive enhancement patterns. In this retrospective single-center study, 104 patients with incidentally detected small hyperechoic renal masses underwent CEUS between December 2021 and July 2024. Two blinded radiologists independently assessed wash-in and wash-out dynamics, peak intensity, homogeneity, and perilesional rim-like enhancement. Histopathology was obtained when available; lesions with ≥ 18 months of stable imaging follow-up were considered benign. Diagnostic metrics, interobserver agreement (ICC), and multivariate logistic regression (IBM SPSS Statistics 29.0) were used to identify independent predictors, reported as odds ratios (ORs) with 95% confidence intervals (CIs). Of 104 lesions, 80 were classified as AMLs and followed with ultrasound, while 28 were biopsied, confirming 26 RCCs (papillary 53%, chromophobe 32%, clear cell 15%) and 2 atypical AMLs. Rapid wash-out (sensitivity = 84%, specificity = 91%, AUC = 0.90) and perilesional rim-like enhancement (specificity = 95%, PPV = 90%) were the strongest CEUS predictors of RCC. Multivariate analysis identified rapid wash-out (OR = 5.0; 95% CI, 2.0-12.0) and perilesional enhancement (OR = 3.8; 95% CI, 1.5-10.0) as independent predictors. Combined CEUS features achieved an AUC = 0.93. Interobserver agreement was good (ICC 0.75-0.9). CEUS accurately differentiates RCC from AML in small hyperechoic renal masses. Rapid wash-out and perilesional rim-like enhancement are independent predictors of malignancy and may guide biopsy versus surveillance decisions.

Introduction: Small hyperechoic renal masses are frequently detected incidentally on conventional ultrasound and are often presumed to represent benign lesions, particularly angiomyolipomas. However, malignant renal tumors, including renal cell carcinoma, may also appear hyperechoic when small, creating a diagnostic challenge at first-line imaging. This study aimed to evaluate the feasibility and exploratory diagnostic performance of B-mode ultrasound radiomics for differentiating benign and malignant small hyperechoic renal masses. Methods: This retrospective single-center study included adult patients with incidentally detected small hyperechoic renal masses measuring ≤3 cm and examined between July 2022 and April 2025. All lesions underwent standardized B-mode ultrasound assessment and multidisciplinary review. Final diagnosis was established by histopathology when available or by longitudinal ultrasound follow-up stability for lesions considered benign. Lesions were manually segmented on representative B-mode DICOM images, and original radiomic features were extracted using PyRadiomics version 3.0 according to standardized definitions compatible with the Image Biomarker Standardisation Initiative framework. A total of 114 original radiomic features were extracted from each lesion. The primary comparison was benign versus malignant lesions. Diagnostic performance was assessed using feature-level receiver operating characteristic analysis. Results: Forty-two lesions were included in the final radiomic cohort, including 26 malignant renal cell carcinomas and 16 benign angiomyolipomas. Malignant lesions included papillary renal cell carcinoma, chromophobe renal cell carcinoma, and clear-cell renal cell carcinoma. All malignant lesions were histologically confirmed. Among benign lesions, 14 angiomyolipomas were classified based on longitudinal ultrasound stability, whereas 2 were confirmed by ultrasound-guided percutaneous biopsy after mild dimensional increase during imaging surveillance. Among the extracted radiomic features, firstorder_Variance and firstorder_MeanAbsoluteDeviation showed the highest exploratory discriminatory performance, each achieving an area under the receiver operating characteristic curve of 0.837. Both features are first-order measures of gray-level dispersion within the segmented lesion. Higher values were observed in malignant lesions, suggesting greater intralesional grayscale heterogeneity compared with benign angiomyolipomas. Conclusions: B-mode ultrasound radiomics is feasible for the quantitative assessment of small hyperechoic renal masses and may provide complementary information for differentiating benign angiomyolipomas from malignant renal cell carcinomas. firstorder_Variance emerged as a representative candidate imaging biomarker of grayscale dispersion, with firstorder_MeanAbsoluteDeviation showing concordant performance as a related dispersion measure. These findings should be considered preliminary and hypothesis-generating and require validation in larger multicenter cohorts before clinical implementation.