What is the best next imaging step for a 3.6 cm renal mass that has increased in size, computed tomography (CT) scan or magnetic resonance imaging (MRI)?

Next Imaging for a Growing 3.6 cm Renal Mass

CT of the abdomen with IV contrast is the preferred next imaging step for a 3.6 cm renal mass that has increased in size while under surveillance. 1

Rationale for CT Abdomen with IV Contrast

CT imaging is the most appropriate choice for several key reasons:

1. Established surveillance method: CT of the abdomen is the most commonly used method for surveillance of renal masses and provides excellent characterization of growth patterns 1

2. Accurate measurement: CT allows for precise measurement of the mass with relatively low interobserver and intraobserver variability (3.1 mm and 2.3 mm respectively) 1

3. Enhanced characterization: CT with IV contrast provides detailed information about:

   • Enhancement patterns
   • Internal characteristics
   • Relationship to surrounding structures
   • Potential invasion of adjacent tissues

4. Metastatic evaluation: CT can assess for regional lymphadenopathy and potential metastatic spread, particularly important for a mass that has demonstrated growth 1

Why CT is Preferred Over MRI in This Case

While MRI is also considered appropriate for renal mass evaluation, CT has several advantages in this specific scenario:

• Established baseline: Since the patient has been under surveillance since 2021, prior imaging was likely CT-based, making direct comparison more reliable
• Growth documentation: CT provides more consistent measurements between studies, critical when evaluating growth rates 1
• Efficiency: CT is more widely available, faster to perform, and less susceptible to motion artifacts

Imaging Protocol Recommendations

The optimal CT protocol should include:

• CT abdomen with IV contrast (not abdomen/pelvis, as pelvic imaging has limited benefit for renal mass surveillance) 1
• Consider including chest CT if there are concerns about potential metastatic disease, particularly with a growing mass 1
• Thin-section acquisition for optimal characterization

Clinical Considerations

The 3.6 cm size and documented growth are concerning features that warrant careful evaluation:

• Masses >3 cm have higher likelihood of malignancy
• Growth during surveillance is a significant risk factor for renal cell carcinoma
• The specific growth rate should be calculated to help determine management strategy

Common Pitfalls to Avoid

1. Measurement inconsistency: Using different imaging modalities can result in inconsistent measurements that affect clinical decision-making 1

2. Inadequate contrast timing: Proper contrast timing is essential for accurate enhancement evaluation

3. Limited follow-up: Given the documented growth, this mass now requires more definitive evaluation and likely intervention rather than continued surveillance

4. Overlooking the chest: Consider including chest imaging as part of the evaluation, as pulmonary metastases are common with renal cell carcinoma 1

CT abdomen with IV contrast represents the most appropriate next imaging step for this growing renal mass, providing the most reliable information to guide subsequent management decisions.