Role of US Contrast Agents in the Assessment of Indeterminate Solid and Cystic Lesions in Native and Transplant Kidneys

Abstract

Ultrasonography (US) is often the initial imaging modality employed in the evaluation of renal diseases. Despite improvements in B-mode and Doppler imaging, US still faces limitations in the assessment of focal renal masses and complex cysts as well as the microcirculation. The applications of contrast-enhanced US (CEUS) in the kidneys have dramatically increased to overcome these shortcomings with guidelines underlining their importance. This article describes microbubble contrast agents and their role in renal imaging. Microbubble contrast agents consist of a low solubility complex gas surrounded by a phospholipid shell. Microbubbles are extremely safe and well-tolerated pure intravascular agents that can be used in renal failure and obstruction, where computed tomographic (CT) and magnetic resonance (MR) imaging contrast agents may have deleterious effects. Their intravascular distribution allows for quantitative perfusion analysis of the microcirculation, diagnosis of vascular problems, and qualitative assessment of tumor vascularity and enhancement patterns. Low acoustic power real-time prolonged imaging can be performed without exposure to ionizing radiation and at lower cost than CT or MR imaging. CEUS can accurately distinguish pseudotumors from true tumors. CEUS has been shown to be more accurate than unenhanced US and rivals contrast material-enhanced CT in the diagnosis of malignancy in complex cystic renal lesions and can upstage the Bosniak category. CEUS can demonstrate specific enhancement patterns allowing the differentiation of benign and malignant solid tumors as well as focal inflammatory lesions. In conclusion, CEUS is useful in the characterization of indeterminate renal masses and cysts.

Persistent fetal lobulation of kidney mimicking renal tumour

“…Contrast enhanced ultrasound (CEUS) is the imaging modality comprising the use of sonography along with ultrasound contrast agents 12. It uses microbubbles to overcome the pitfalls associated with conventional ultrasound to characterise renal masses by differentiating between the anatomic variation and renal lesion.…”

Enhancing the role of paediatric ultrasound with microbubbles: a review of intravenous applications

“…applications of CEUS in the kidneys have been mainly evaluated in adults and include differentiation of tumours from pseudotumours, benign and malignant lesions and characterization of complex cysts. 7,71 CEUS was reported to accurately delineate renal cortical necrosis in a child sustaining trauma and could be used for the diagnosis of acute renal transplant rejection or other vascular complications after transplantation in the future. 72 Based on currently available recommendations, CEUS can be used to grade disease activity and extent in adult patients with inflammatory bowel disease and differentiate active inflammation from chronic fibrosis in intestinal loops.…”

Romanian National Guidelines on Contrast Enhanced Ultrasound in clinical practice

“…The enhancement pattern of pseudotumours mirrors that of the surrounding parenchyma in all phases. Any other enhancing pattern should be considered suspicious for malignancy [107,109,110].…”

“…The differentiation between renal cell carcinomas (RCCs) and various benign entities, such as angiomyolipomas or oncocytomas is difficult [113], therefore CEUS alone is not recommended for the purpose of characterising solid lesions [109]. The typical enhancement pattern of solid RCCs includes a rapid "wash-in" phase, with a hyper-enhanced appearance at peak enhancement, followed by "wash-out" [107,109,110].…”