Diagnostic evaluation of renal masses in chronic kidney disease: a clinical and radiologic challenge.

Chronic kidney disease (CKD) increases the risk of renal cell carcinoma (RCC), particularly with long-term dialysis exposure and acquired cystic kidney disease (ACKD). At the same time, CKD-related architectural distortion and hypoperfusion reduce lesion conspicuity on ultrasound and weaken enhancement-based interpretation on CT and MRI. In advanced CKD, restrictions on iodinated and gadolinium-based contrast agents further increase the proportion of renal masses that remain indeterminate after conventional imaging. Contrast-enhanced ultrasound (CEUS) addresses the key unmet need in this setting: a safe, direct assessment of microvascular perfusion. Microbubble agents are purely intravascular and non-nephrotoxic, enabling use across all CKD stages and in dialysis patients. By showing real-time enhancement of septa, wall thickening and mural nodules, CEUS distinguishes vascular tumour components from avascular hemorrhagic or proteinaceous material that can mimic enhancement on CT/DECT or signal abnormalities on non-contrast MRI. This capability supports a CEUS-adapted Bosniak approach: lesion categorization is driven by enhancement of septa, wall and nodules rather than by attenuation or T1 hyperintensity of cyst contents, helping avoid misclassification in ACKD. We propose a structured workflow that integrates the triad of CKD stage/eGFR, dialysis status and ACKD with pre- and post-CEUS Bosniak assessment to guide follow-up versus biopsy or nephron-sparing treatment. This article is a narrative review of the literature, complemented by an illustrative clinical case which demonstrates how CEUS can resolve ambiguity when CT/DECT and non-contrast MRI remain inconclusive.