What is the recommended management for an asymptomatic 22-year-old male with an incidental 7.1 mm left lower‑pole renal lesion of intermediate density on contrast‑enhanced CT enterography?

Management of a 7.1 mm Indeterminate Renal Lesion in a Young Adult

This 7.1 mm intermediate-density renal lesion requires dedicated multiphase contrast-enhanced CT or MRI for definitive characterization, followed by urologic consultation if any enhancement is detected. 1, 2

Immediate Next Steps

Obtain Dedicated Renal Imaging with Contrast

• Request the patient bring the CT enterography images on disk for direct review, as the initial study was optimized for bowel evaluation, not renal mass characterization 1, 2
• Order a multiphase contrast-enhanced CT (without and with IV contrast) or gadolinium-enhanced MRI as the definitive next imaging study 1, 2
• MRI offers superior specificity (68% vs 27% for CT) for distinguishing solid components in small renal lesions and should be strongly considered, particularly given the patient's young age and desire to minimize radiation exposure 1, 2

Key Imaging Criteria to Determine Management

• Enhancement of ≥10-15 HU on CT or ≥15% on MRI indicates a solid mass requiring urologic referral 2, 3
• Homogeneous lesions measuring <20 HU or >70 HU on unenhanced CT are benign and require no further workup 1, 2
• Lesions containing macroscopic fat suggest angiomyolipoma (benign), though lipid-poor variants can mimic renal cell carcinoma 1, 2

Risk Stratification Based on Size and Age

Why This Lesion Warrants Careful Evaluation

• At 7.1 mm, this falls into the small renal mass category (T1a, <4 cm) where approximately 20-30% may be benign (oncocytoma, fat-poor angiomyolipoma) 1, 2
• However, the "intermediate density" descriptor on CT enterography is concerning because it suggests the lesion is neither clearly cystic (<20 HU) nor clearly hyperdense/benign (>70 HU) 1, 2
• The patient's young age (22 years) is atypical for renal cell carcinoma (median age 60 years), but does not exclude malignancy 1

Management Algorithm Based on Imaging Results

If Enhancement is Detected (Solid Mass)

• Refer to urology immediately for discussion of management options 1, 2
• Management options include:
  • Active surveillance with repeat imaging at 3-6 months, then periodically based on growth kinetics—this is increasingly accepted for small renal masses given their indolent behavior 1, 2
  • Percutaneous renal mass biopsy to guide decision-making, particularly valuable in young patients where avoiding unnecessary surgery is paramount 1, 2
  • Definitive intervention (partial nephrectomy or ablation) if biopsy confirms malignancy or if growth is documented 2

If No Enhancement is Detected (Cystic Lesion)

• Classify using the 2019 Bosniak system 2:
  • Bosniak I/II: No follow-up needed (0-15.6% malignancy risk) 2
  • Bosniak IIF: Refer to urology for surveillance plan (10.9-25% progression risk) 2
  • Bosniak III: Urologic referral for discussion of surveillance vs. biopsy (40-54% malignancy rate) 2
  • Bosniak IV: Urgent urologic referral (84-90% malignancy rate) 2

Role of Renal Mass Biopsy in This Case

When to Consider Biopsy

• Strongly consider biopsy if imaging shows a solid enhancing mass, given this patient's young age and the 20-30% chance of benign pathology 1, 2
• Biopsy yields diagnostic results in 78-97% of cases with low complication rates (~0.9%) 1, 2
• A nondiagnostic biopsy cannot be interpreted as evidence of benignity—repeat biopsy or surgical excision is required 1, 2

Benefits of Biopsy in Young Patients

• Prevents unnecessary surgery in cases of benign tumors (oncocytoma, fat-poor AML) 1, 2
• Allows informed decision-making between active surveillance and intervention 1, 2
• Particularly valuable when imaging features suggest possible benign pathology 1, 2

Critical Pitfalls to Avoid

Do Not Rely on CT Enterography Alone

• CT enterography is not optimized for renal mass characterization—it lacks the dedicated pre-contrast and delayed phases needed to assess enhancement accurately 1, 2
• The "intermediate density" descriptor is insufficient for clinical decision-making 1, 2

Do Not Delay Definitive Imaging

• Waiting 6 months for repeat imaging without first obtaining proper characterization is inappropriate 1, 2
• The initial dedicated contrast study should occur within 4-6 weeks to establish a baseline and determine if the lesion is solid or cystic 2

Do Not Assume Benignity Based on Size Alone

• While many small renal masses are indolent, up to 8% of hyperechoic/hyperdense lesions can be renal cell carcinoma 3
• Growth rate >5 mm/year is a red flag requiring biopsy or intervention 3

Baseline Workup if Solid Mass is Confirmed

Laboratory Studies

• Comprehensive metabolic panel (assess renal function, calcium) 2
• Complete blood count (evaluate for anemia, erythrocytosis) 2
• Urinalysis (assess for hematuria) 2

Staging Imaging (Only if Malignancy Suspected)

• Chest CT to screen for pulmonary metastases (most common distant site for RCC) 1, 2
• Routine bone or brain imaging is not indicated unless symptomatic 2

Addressing the Varicocele

The mild left varicocele is unrelated to the renal lesion and observation is appropriate given the patient is asymptomatic. However, ensure the renal imaging evaluates the left renal vein for any compression or thrombosis that could cause secondary varicocele, though this is unlikely with a 7.1 mm lower pole lesion. 1