In a 68-year-old woman with left-sided hydroureteronephrosis and a 1.2 cm enhancing lower-pole renal lesion on computed tomography urography (CTU) that could represent papillary renal cell carcinoma, what is the recommended diagnostic work‑up and management?

Management of 1.2 cm Enhancing Renal Mass Suspicious for Papillary RCC

For this 68-year-old woman with a 1.2 cm enhancing lower-pole renal lesion suspicious for papillary RCC, obtain a renal mass biopsy to confirm the diagnosis and guide management, as this small lesion is amenable to active surveillance if confirmed as low-grade papillary RCC or may be benign. 1

Diagnostic Work-Up

Complete the Imaging Evaluation First

The CTU has identified an indeterminate enhancing mass. Before proceeding to biopsy, ensure optimal imaging characterization:

• If the lesion shows equivocal enhancement on CTU, obtain MRI abdomen with and without IV contrast or contrast-enhanced ultrasound (CEUS) to better characterize vascularity 2
  • Papillary RCC characteristically shows low enhancement compared to other RCC subtypes due to low vascular density 3, 4
  • MRI is more sensitive than CT for detecting subtle enhancement in hypovascular lesions 2
  • Critical pitfall: Up to 22% of papillary RCCs demonstrate attenuation <20 HU on non-contrast CT, mimicking simple cysts 4

Obtain Percutaneous Renal Mass Biopsy

Renal mass biopsy is strongly recommended for this case because:

• The 2025 EAU guidelines explicitly state that percutaneous renal mass biopsy "avoids unnecessary interventions for benign lesions and supports selection of patients for surveillance" 1
• Core needle biopsy (not fine needle aspiration) via coaxial technique has 78-97% diagnostic yield with 98-100% specificity and 86-100% sensitivity for malignancy 1
• Approximately one-third of biopsied small renal masses prove to be benign (lipid-poor angiomyolipoma, oncocytoma) 2
• Biopsy results directly influence whether active surveillance versus intervention is appropriate 1, 2

Technical considerations:

• Use core needle biopsy with coaxial technique to minimize seeding risk 1
• If initial biopsy is nondiagnostic, consider repeat biopsy or surgical resection 1

Staging Work-Up

Complete staging evaluation should include:

• Chest CT to evaluate for pulmonary metastases
• Brain imaging is NOT indicated unless the patient has metastatic disease 1
• Laboratory evaluation including renal function

Treatment Approach

Active Surveillance is a Viable Option

For a 1.2 cm renal mass, particularly if biopsy confirms papillary RCC:

• Active surveillance is appropriate for small renal masses, especially papillary RCC which demonstrates slow growth kinetics 2
• Many small RCCs show low progression rates 2
• This approach minimizes kidney function loss while maintaining oncologic safety 2

Surgical Options if Intervention Chosen

If the patient and physician opt for definitive treatment:

• Partial nephrectomy is preferred over radical nephrectomy for small renal masses to preserve renal function
• Consider nephron-sparing approaches given the small size and lower pole location
• Use RENAL or PADUA nephrometry scores to assess surgical complexity 1

Shared Decision-Making is Essential

The 2025 EAU guidelines emphasize using a shared decision-making approach when deciding on treatment for RCC, incorporating patient preferences, comorbidities, and life expectancy 1

Key Clinical Pitfalls to Avoid

1. Do not assume low attenuation = benign cyst: Over 20% of papillary RCCs can appear hypodense on CT 4
2. Do not skip biopsy for small masses: Biopsy prevents unnecessary surgery in up to one-third of cases that prove benign 2
3. Do not use enhancement thresholds alone: While papillary RCC typically shows modest enhancement (mean 50-60 HU), there is significant overlap with other entities 5
4. Address the hydroureteronephrosis: Ensure this is related to the mass location and not a separate obstructive process requiring intervention

Addressing the Hydroureteronephrosis

The left-sided hydroureteronephrosis needs correlation:

• Determine if this is caused by the lower pole mass or represents a separate pathology
• If the mass is causing obstruction, this may influence the decision toward intervention rather than surveillance
• Urinary tract infiltration by the tumor is uncommon (3.6% of cases) but suggests malignancy 5