What is the next step in management for a patient with renal lesions, including a 5.5 mm hyperdense focal lesion and a 13 mm peripherally calcified lesion, identified on imaging?

Management of Small Renal Lesions Identified on Imaging

The next step in management for this patient with multiple small renal lesions should be a dedicated multiphase contrast-enhanced CT or MRI of the kidneys to better characterize these lesions. 1

Assessment of the Current Findings

The imaging findings show:

• 5.5 mm hyperdense focal lesion in the left kidney upper pole (possible proteinaceous cyst)
• 6.2 mm hypodense lesion in the right kidney midpole
• 4.8 mm hypodense lesion in the left kidney midpole
• 13 mm peripherally calcified lesion in the right kidney lower pole

Initial Characterization Based on Size

• Small renal masses <1.5 cm (like the 5.5 mm, 6.2 mm, and 4.8 mm lesions) are challenging to evaluate due to partial volume averaging and pseudoenhancement on CT 1
• The smaller lesions (<1 cm) are particularly difficult to characterize accurately on initial imaging 2
• The 13 mm peripherally calcified lesion requires further evaluation as it is in the size range where characterization becomes more reliable 1

Recommended Next Steps

1. Dedicated Renal Mass Protocol Imaging

• Multiphase contrast-enhanced CT or MRI: This is the optimal next step to properly characterize indeterminate renal lesions 1
  • CT with and without IV contrast is preferred for initial evaluation of indeterminate renal masses 1
  • MRI without and with IV contrast is an excellent alternative, especially for lesions <1.5 cm due to its higher specificity for small cysts 1

2. Specific Imaging Considerations

• For the hyperdense 5.5 mm lesion:

  • MRI may better differentiate between a hemorrhagic/proteinaceous cyst and solid mass 1
  • On MRI, homogeneous high T1 signal intensity lesions with smooth borders and lesion-to-renal parenchyma signal intensity ratio >1.6 suggest benign cysts 1

• For the peripherally calcified 13 mm lesion:

  • Dedicated multiphase imaging will help determine if there are enhancing components 1
  • CT is superior to MRI for detecting calcifications 1

3. Follow-up Protocol

• If lesions remain indeterminate after dedicated imaging:
  • For lesions <1 cm: Follow-up imaging in 6-12 months 1, 3
  • For the 13 mm lesion: Consider follow-up in 6 months if classified as Bosniak IIF 3
  • Lesions that show growth or increasing complexity during follow-up warrant further evaluation 3

Potential Management Pathways

If Lesions Are Characterized as Simple or Minimally Complex Cysts

• For Bosniak I and II cysts: No further follow-up needed 1
• For Bosniak IIF cysts: Follow-up imaging at 6 months initially, then annually for at least 5 years 3
  • A study of 42 Bosniak IIF cysts showed that only 2 (4.8%) progressed to malignancy during an average follow-up of 5.8 years 3

If Lesions Remain Indeterminate After Dedicated Imaging

• For lesions ≤1 cm: Surveillance imaging is appropriate as detection rates with both CT and US are limited for these tiny lesions 2
• For the 13 mm lesion if still indeterminate: Consider renal mass biopsy 1, 4
  • Renal mass biopsy can provide a definitive diagnosis in approximately 87% of cases 4

If Lesions Are Suspicious for Malignancy

• For the 13 mm lesion if suspicious: Consider biopsy before treatment decisions 1, 4
• For small lesions <1 cm: Active surveillance with repeat imaging is appropriate 1

Important Considerations and Pitfalls

• Avoid immediate intervention without proper characterization: About 33% of patients with indeterminate renal lesions undergo immediate treatment without subsequent imaging or biopsy, resulting in a 10% rate of benign pathology at surgery 4

• Be cautious with small lesions: A substantial proportion of lesions under 1 cm may not be detected with either CT or MRI, and characterization is challenging 2

• Consider specialized techniques:

  • Thin-section CT (5 mm vs. standard 10 mm) can help reduce partial volume averaging artifacts 5
  • Subtraction techniques on MRI can improve assessment of enhancement in intrinsically hyperintense lesions 1

• Consistent follow-up: If follow-up is chosen, use the same imaging modality and technique for consistent measurements 1