What MRI protocol to order for a renal mass?

From the Guidelines

For a renal mass protocol MRI, I recommend ordering an MRI abdomen with and without IV contrast, as it is usually appropriate for the initial imaging of an indeterminate renal mass in patients without contraindications to gadolinium-based MR IV contrast, according to the ACR Appropriateness Criteria 1. This recommendation is based on the most recent guidelines, which suggest that MRI abdomen with and without IV contrast is an equivalent alternative to CT abdomen with and without IV contrast for the initial imaging of an indeterminate renal mass in patients without contraindications to either iodinated CT contrast or gadolinium-based MR IV contrast. The MRI protocol should include:

• T1-weighted, T2-weighted, and dynamic contrast-enhanced sequences with pre-contrast, arterial, venous, and delayed post-contrast phases
• Gadolinium-based contrast agents (unless contraindicated) with a standard dose of 0.1 mmol/kg
• Diffusion-weighted imaging (DWI) with multiple b-values to help characterize the mass
• Fat-suppression techniques to detect fat components within potential angiomyolipomas
• Thin slices (3-5 mm) through the kidneys for detailed evaluation This comprehensive protocol allows for characterization of renal masses by assessing enhancement patterns, presence of fat, diffusion restriction, and relationship to collecting systems and surrounding structures, guiding appropriate management decisions, as suggested by the ACR Appropriateness Criteria 1. In patients with contraindications to gadolinium-based MR IV contrast, an MRI abdomen without IV contrast or US abdomen with IV contrast may be considered, as they are usually appropriate for the initial imaging of an indeterminate renal mass in such patients, according to the ACR Appropriateness Criteria 1.

From the Research

MRI Protocol for Renal Mass

To evaluate renal masses, a core MRI protocol should include:

• T1-weighted sequence with in- and opposed-phase images (or, alternatively with DIXON technique) 2
• T2-weighted and diffusion-weighted images 2, 3
• Dynamic contrast-enhanced sequence with subtraction images, followed by a delayed post-contrast T1-weighted sequence 2, 3
• Chemical-shift imaging (CSI) to detect intra-lesional fat 3
• Magnetic resonance urography (MRU) using conventional extracellular gadolinium or gadoxetic acid enhanced urography 3

Advantages of MRI

The main advantages of MRI over computed tomography include:

• Increased sensitivity for contrast enhancement 2, 4
• Less sensitivity for detection of calcifications 2
• Absence of pseudoenhancement 2
• Lack of radiation exposure 2

Specific MRI Sequences

• Diffusion-weighted imaging (DWI) can replace conventional fat-suppressed T2W and can be performed free-breathing (FB) with two b-values 3
• T2-weighted imaging (T2W) can help characterize solid renal masses, with increased T2 signal intensity specific for renal cell carcinoma (RCC) 3
• Dynamic contrast enhancement (DCE) can help evaluate the vascularity of renal masses and predict RCC subtype 3

Bosniak Classification

The Bosniak classification has been updated to include MRI, with specific definitions of imaging terms to improve interobserver agreement and specificity for malignancy 5

• MRI can be used to evaluate masses that at computed tomography (CT) have abundant thick or nodular calcifications, are homogeneous and hyperattenuating, or are heterogeneous and nonenhancing 5