Prospective evaluation of CT indeterminate renal masses using US and contrast-enhanced ultrasound.

OBJECTIVE: The aim of this study was to assess the accuracy of Ultrasound (US) and contrast-enhanced ultrasound (CEUS) in the characterization of renal nodules indeterminate on CT by identifying benign cystic lesions not requiring further examination.

METHODS: 72 patients with 83 indeterminate renal nodules on CT underwent baseline US and CEUS that classified lesions as benign (Bosniak I, II or IIF cysts) or potentially malignant (Bosniak III or IV cysts, solid nodules). The accuracy of US and CEUS in the differentiation between benign cysts and potentially malignant nodules was analyzed and compared with the final diagnosis obtained by histology or follow-up of at least 23 months with CEUS ± a conclusive CT/MR study.

RESULTS: Final diagnoses comprised 50 benign complex cysts, 1 focal nephritis, 1 multilocular cystic nephroma, 3 oncocytomas, 1 transitional cell carcinoma and 27 renal cell carcinomas. Unenhanced US correctly classified 18/50 (36%) benign cysts and 17/33 (51.5%) of the potentially malignant lesions obtaining a sensitivity of 36%, specificity of 51.5%, and overall accuracy of 42.2%. The addition of CEUS allowed a correct diagnosis of 48 /50 (96%) benign cysts and of 31/33 (93.9%) nodules as potentially malignant, with a sensitivity of 96%, specificity of 93.9%, and overall accuracy of 95.2%.

CONCLUSION: CEUS is very useful in the differentiation between benign complex cysts and other lesions that require further investigation in non-conclusive renal nodules detected on CT, improving the accuracy of baseline US from 42.2 to 95.2%.