What is the initial workup for a renal mass?

Initial Workup for Renal Masses

The initial workup for a renal mass requires high-quality cross-sectional imaging with CT abdomen without and with IV contrast (or MRI if CT is contraindicated), comprehensive laboratory evaluation including metabolic panel and CBC, and chest imaging to assess for metastases. 1

Imaging Evaluation

Primary Imaging Modality

• CT abdomen without and with IV contrast is the gold standard for initial characterization and staging of renal masses, with diagnostic accuracy of 79.4% for predicting renal cell carcinoma in small masses 2
• The protocol must include both unenhanced and contrast-enhanced phases to assess for enhancement, which is critical for distinguishing benign from malignant lesions 2
• Multiphase imaging (corticomedullary and nephrographic phases) provides optimal characterization and helps differentiate RCC subtypes 2

Alternative Imaging When CT Contraindicated

• MRI abdomen without and with IV contrast is the preferred alternative when iodinated contrast is contraindicated due to allergy or renal insufficiency 2, 1
• MRI sequences should include T2-weighted, chemical shift T1-weighted, contrast-enhanced T1-weighted, and diffusion-weighted images 2, 3
• Unenhanced MRI has advantages over unenhanced CT for characterizing renal masses when contrast cannot be given 2

Chest Imaging for Metastatic Evaluation

• Chest imaging is mandatory for accurate staging—either chest radiograph or CT scan 2, 1
• Chest CT is preferred over chest radiography for detecting pulmonary metastases, though radiography is commonly used due to concerns about false-positive findings with CT 2

Laboratory Evaluation

Obtain the following laboratory tests in all patients: 1

• Comprehensive metabolic panel (including serum creatinine, liver function tests, serum calcium, lactate dehydrogenase)
• Complete blood count (hemoglobin, leukocyte and platelet counts)
• Urinalysis
• Coagulation profile 2
• Classify chronic kidney disease stage based on eGFR and proteinuria 1

Physical Examination

Focus the physical examination on specific findings: 4

• Assess for supraclavicular adenopathy, abdominal mass, lower extremity edema, varicocele, or subcutaneous nodules 2
• Evaluate vital signs for hemodynamic compromise 4
• Determine mass location, size, consistency, mobility, and pulsatility 4

Additional Imaging Considerations

When to Add Brain or Bone Imaging

• Brain CT or MRI is NOT routine unless neurological signs or symptoms are present 2, 1, 3
• Bone scan is NOT routine unless elevated alkaline phosphatase or bone pain is present 2, 1
• PET scan is not part of routine initial workup 2

Pelvis Imaging

• Imaging of the pelvis has limited benefit for metastasis detection and is considered optional 2, 3
• CT abdomen and pelvis may be obtained but is not mandatory for initial evaluation 2

Role of Renal Mass Biopsy

Biopsy is NOT the initial workup but has expanded indications: 2, 1

• Consider biopsy before ablative therapies to confirm histology 1
• Consider biopsy in metastatic disease before systemic treatment 1
• Consider biopsy when imaging features suggest benign lesions (e.g., lipid-poor angiomyolipoma) to avoid unnecessary surgery 2
• Consider biopsy in patients with limited life expectancy or significant comorbidities to guide management 2
• Important limitation: 20% nondiagnostic rate for small masses, and nondiagnostic biopsy cannot be considered evidence of benignity 2

Special Populations

Genetic counseling should be considered for: 1

• All patients ≤46 years of age
• Patients with multifocal or bilateral renal masses
• Personal or family history suggesting familial renal neoplastic syndrome (von Hippel-Lindau, hereditary leiomyomatosis)

Common Pitfalls to Avoid

• Do not rely on single-phase contrast-enhanced CT alone—unenhanced images are essential to detect macroscopic fat in angiomyolipomas and to accurately assess enhancement 2
• Small masses (<1.5 cm) are challenging due to pseudoenhancement and partial volume averaging—consider MRI for problem-solving 2
• Homogeneous masses <20 HU or >70 HU on noncontrast CT can be characterized as benign without contrast 2
• Central renal masses may suggest urothelial carcinoma—consider urine cytology or ureteroscopy 2
• Do not skip chest imaging—metastatic evaluation is essential even for small masses 1