What is the recommended CECT (Contrast-Enhanced Computed Tomography) protocol for a renal mass?

Recommended CECT Protocol for Renal Mass Evaluation

For evaluating a renal mass, a multiphase CT protocol including unenhanced, corticomedullary/arterial, and nephrographic phases with thin-slice acquisition (≤5mm) is the recommended approach. 1, 2

Protocol Components

Essential Phases

1. Unenhanced (Non-contrast) Phase

   • Critical for detecting calcifications and measuring baseline attenuation
   • Allows identification of macroscopic fat in angiomyolipomas
   • Helps differentiate pseudoenhancement from true enhancement in small lesions
   • Essential for characterizing homogenous masses (<20 HU or >70 HU are typically benign)

2. Corticomedullary/Arterial Phase

   • Obtained 25-40 seconds after contrast injection
   • Best for assessing tumor vascularity and enhancement patterns
   • Critical for differentiating RCC subtypes (particularly clear cell RCC)
   • Provides 100% sensitivity for local recurrence detection after ablation 1

3. Nephrographic Phase

   • Obtained 70-90 seconds after contrast injection
   • Optimal for detecting small renal masses
   • Provides better lesion-to-parenchyma contrast
   • Essential for evaluating enhancement of cystic components

Technical Parameters

• Slice thickness: ≤5mm (thin-slice acquisition)
• Reconstruction: Multiplanar reformatting recommended
• Contrast administration: Weight-based dosing of high-concentration iodinated contrast

Special Considerations

Cystic Renal Masses

• The Bosniak classification system requires assessment of enhancing nodules, walls, or septa within cystic masses 1
• Both unenhanced and contrast-enhanced phases are necessary for accurate classification
• Enhancement pattern is key to determining malignancy probability

Solid Renal Masses

• Enhancement pattern on multiphasic CT helps subtype RCC
• Aorta-based corrected attenuation values in the corticomedullary phase show 88-90% accuracy in differentiating clear cell RCC from other subtypes 3
• A cut-off of 86-89 HU in the corticomedullary phase has 81-86% accuracy for identifying clear cell RCC 3

Small Renal Masses

• Small masses (≤1.5 cm) are challenging to evaluate due to pseudoenhancement and partial volume averaging 1
• Dual-energy CT can help overcome pseudoenhancement issues and differentiate solid tumors from hyperdense cysts 1

Alternative Imaging Options

When CT with contrast is contraindicated:

• MRI with gadolinium: Similar diagnostic performance to CT
• Contrast-enhanced ultrasound (CEUS): Useful for differentiating cystic from solid lesions and characterizing complex renal masses 4
• Tc-99m sestamibi SPECT/CT: Helpful when oncocytoma is suspected 1

Coding Considerations

• Use ICD-10 code D41.0 (Neoplasm of uncertain behavior of kidney) for initial evaluation 2
• Use R93.4 when the mass was initially detected on another imaging modality 2

Common Pitfalls

• Relying solely on single-phase imaging, which may miss enhancement patterns critical for diagnosis
• Failure to obtain an unenhanced phase, which is essential for detecting fat and measuring true enhancement
• Inadequate thin-slice acquisition, which may miss small enhancing components
• Misinterpreting pseudoenhancement as true enhancement in small renal masses

The multiphase CT protocol provides complementary information that is essential for accurate characterization of renal masses, which directly impacts patient management decisions regarding surgery, ablation, biopsy, or active surveillance.