Diagnostic Value of Contrast-Enhanced Ultrasound in Renal Masses Remaining Indeterminate After Contrast-Enhanced CT and Contrast-Enhanced MRI

Some renal masses remain indeterminate after both contrast-enhanced CT (CE-CT) and contrast-enhanced MRI (CE-MRI), with uncertainty concerning their cystic or solid composition, raising an issue in patient management. The aim of this article was to assess the diagnostic performance of contrast-enhanced ultrasound (CEUS) in the characterization of indeterminate renal masses in this specific context. Starting from CEUS examinations investigating renal masses, we retrospectively identified patients with renal masses that remained indeterminate after both unenhanced and enhanced CT and MRI. CEUS examinations were performed in a single center between February 2009 and September 2019. Cross-sectional imaging and nonenhanced US images were individually reviewed to confirm each lesion's indeterminate nature. CEUS was performed to differentiate solid and cystic lesions. CEUS findings were correlated to pathologic analysis or follow-up (minimum 3 y) to assess diagnostic performance. Inter-reader agreement was also analyzed. Sixty-four patients [mean age: 60.5±12.1 (SD), 49 men; 15 women] with 73 indeterminate renal masses (median: 24 mm, range: 10 to 122 mm) were identified. CEUS enabled further characterization of 71 out of the 73 indeterminate lesions (97.3%). To establish the solid nature of a renal mass, CEUS had a sensitivity of 81.3% (95% CI: 54.5%-95.9%), a specificity of 98.2% (95% CI: 90.3%-99.9%), a positive predictive value of 92.9% (95% CI: 64.8%-98.9%), a negative predictive value of 94.7% (95% CI: 86.6%-98.0%), and an accuracy of 94.4% (95% CI: 86.2%-98.4%), with excellent inter-reader agreement. CEUS can accurately distinguish solid from cystic lesions in renal masses indeterminate after CE-CT and CE-MRI.