Imaging Protocols for Complex Renal Lesions

Primary Imaging Protocol

The American College of Radiology recommends performing CT abdomen without and with IV contrast using a dedicated multiphase renal protocol for complex renal lesions, which includes precontrast, corticomedullary, nephrographic, and excretory phases 1, 2
Thin-section CT acquisition is critical for evaluating small renal masses due to pseudoenhancement and partial volume averaging effects 1
The precontrast phase is essential for detecting macroscopic fat and establishing baseline attenuation values to accurately measure enhancement 1

MRI abdomen without and with IV contrast is equally appropriate for complex renal lesions and offers superior specificity for distinguishing benign from malignant masses, with sequences including T2-weighted images, chemical shift T1-weighted images, contrast-enhanced T1-weighted images, and diffusion-weighted images 5, 2

For cystic lesions, both precontrast and postcontrast phases are mandatory to detect enhancing nodules, walls, or thick septa, with the Bosniak classification determining malignancy risk 1
For solid lesions, thin-section unenhanced CT is necessary to detect small amounts of macroscopic fat, indicating benign angiomyolipoma with virtual certainty 1

Dual-energy CT can differentiate solid tumors from hyperdense cysts on single-phase postcontrast CT and overcome pseudoenhancement artifacts when comprehensive multiphase renal protocol CT is not available 2
If both iodinated CT contrast and gadolinium-based MR contrast are contraindicated, consider contrast-enhanced ultrasound with microbubble agents for real-time evaluation of microvasculature 2

Do not rely on single-phase contrast-enhanced CT for complex lesions, as this prevents accurate assessment of enhancement and determining malignancy risk 1, 2
Do not skip the unenhanced phase, as baseline attenuation values are essential for calculating true enhancement and detecting macroscopic fat 1