Contrast-enhanced US Evaluation of Indeterminate Focal Renal Masses.

Contrast-enhanced US (CEUS) is increasingly used in the characterization of indeterminate focal renal masses. In addition to the safety profile, portability, and relatively low cost of performing a CEUS examination, CEUS may be better tolerated than CT or MRI. US contrast agents (UCAs) are not nephrotoxic, making CEUS the contrast-enhanced examination of choice to safeguard renal function or in patients with kidney failure. CEUS may face technical limitations, including in patients with deep lesions or lesions larger than the field of view, acoustic windows limited by bone or gas, or respiratory motion; technique modification may be needed for a successful examination. As purely intravascular agents, UCAs offer accurate characterization of lesion vascularity. The high temporal resolution of CEUS enables frame-by-frame analysis for detailed assessment of lesion perfusion and can mitigate the effects of patient or respiratory motion. With high contrast and spatial resolution and exquisite sensitivity to even minimal blood flow, CEUS can detect enhancement in hair-thin septa and subcentimeter nodules, making CEUS ideally suited for the characterization and surveillance of cystic renal masses. The high sensitivity of CEUS for intralesional enhancement and its negative predictive value of 100% in excluding flow enable confident discrimination of benign avascular cysts, which require no further follow-up, from solid renal masses, which warrant surveillance or tissue diagnosis. Overall, CEUS performs equally to contrast-enhanced CT or MRI, may be preferred for certain patients or indications, and is appropriate for first-line imaging of indeterminate focal renal masses. ©RSNA, 2026 Supplemental material is available for this article. See the invited commentary by Fetzer in this issue.