Diagnostic Accuracy of Contrast-Enhanced Ultrasound in Differentiating RCC from AML in Small Hyperechoic Renal Masses (≤ 3 cm): A Retrospective Single-Center Study.

BACKGROUND

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.

METHODS

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).

RESULTS

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).

CONCLUSION

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.