What is the recommended approach for evaluating a renal mass in an adult patient with no significant pre-existing conditions?

Evaluation of a Renal Mass in Adults

For an adult patient with a renal mass and no significant pre-existing conditions, obtain high-quality multiphase CT abdomen without and with IV contrast as the primary imaging modality, along with comprehensive metabolic panel, complete blood count, urinalysis, and chest imaging for metastatic evaluation. 1

Imaging Protocol

Multiphase CT abdomen without and with IV contrast is the gold standard for characterizing and staging renal masses, with diagnostic accuracy of 79.4% for predicting renal cell carcinoma in small masses. 1 The protocol must include:

• Unenhanced phase to detect macroscopic fat (indicating benign angiomyolipoma), calcifications, and baseline attenuation values 1
• Corticomedullary phase to assess vascularity and detect enhancement 1
• Nephrographic phase for optimal renal parenchyma evaluation 1
• Excretory phase to evaluate the urothelium if indicated 1

The assessment should specifically characterize tumor complexity, degree of contrast enhancement, and presence or absence of fat. 1

Alternative Imaging When CT Contrast Contraindicated

MRI abdomen without and with IV contrast is the preferred alternative when iodinated contrast is contraindicated due to allergy or renal insufficiency. 2 MRI sequences should include T2-weighted, chemical shift T1-weighted, contrast-enhanced T1-weighted, and diffusion-weighted images. 2

Contrast-enhanced ultrasound (CEUS) using microbubble agents has emerged as a useful alternative, with sensitivity of 100% and specificity of 95% for classifying benign versus malignant renal masses in one study of 1,018 lesions. 1

Laboratory Evaluation

Obtain the following baseline studies in all patients with suspected renal malignancy: 1, 3

• Comprehensive metabolic panel (including serum creatinine, corrected calcium, liver function tests)
• Complete blood count (hemoglobin, leukocyte and platelet counts)
• Urinalysis to assess for hematuria and proteinuria
• Coagulation profile 2

Classify chronic kidney disease stage based on eGFR and degree of proteinuria using KDIGO guidelines, as patients with localized renal cell carcinoma often have multiple risk factors for decreased GFR. 1

Metastatic Evaluation

Chest imaging is mandatory for accurate staging, as the lung is the most common site of metastasis for renal cell carcinoma. 1, 3 Either chest CT or chest radiograph is acceptable, though CT is preferred for detecting pulmonary metastases. 2

Do not routinely obtain bone scintigraphy or brain CT/MRI unless indicated by clinical signs, symptoms, or laboratory abnormalities (elevated alkaline phosphatase, bone pain, neurological symptoms). 3, 2

Physical Examination Findings

Assess specifically for: 2

• Supraclavicular adenopathy
• Palpable abdominal mass
• Lower extremity edema
• Varicocele (may indicate venous involvement)
• Subcutaneous nodules
• Vital signs for hemodynamic compromise

Note that more than 50% of renal masses are now diagnosed incidentally, and the classic triad of hematuria, flank pain, and palpable abdominal mass is typically associated with locally advanced or metastatic disease. 1, 3

Mass Characterization Principles

Benign Features

• Homogeneous masses measuring <20 HU or >70 HU on noncontrast CT can be characterized as benign without contrast administration 1, 2
• Macroscopic fat in a noncalcified solid renal mass indicates benign angiomyolipoma with virtual certainty 1

Cystic Masses

Use the Bosniak classification system to stratify malignancy risk in complex cystic masses. 1 Malignancy rates are:

• Bosniak IIF: 25-38%
• Bosniak III: 40-54%
• Bosniak IV: 90%

Enhancement of nodules, walls, or thick septa within cystic masses is key to determining malignancy probability and requires both unenhanced and contrast-enhanced imaging. 1

Role of Renal Mass Biopsy

Biopsy is not part of initial workup but has expanded indications: 1, 2

• Before ablative therapies
• In metastatic disease before systemic treatment
• When imaging features suggest benign lesions (e.g., fat-poor angiomyolipoma)
• In patients with limited life expectancy or significant comorbidities

Important limitation: Approximately 20% of biopsies are nondiagnostic, especially for small masses, and a nondiagnostic biopsy cannot be considered evidence of benignity. 1, 2

Special Considerations

Genetic counseling should be considered for: 3, 2

• All patients ≤46 years of age
• Patients with multifocal or bilateral renal masses
• Personal or family history suggesting familial renal neoplastic syndrome

Approximately 6-9% of renal cancers have germline mutations in cancer predisposition genes. 3

Critical Pitfalls to Avoid

• Do not rely on single-phase contrast-enhanced CT alone – both unenhanced and enhanced phases are essential for detecting enhancement 2
• Small masses (<1.5 cm) are challenging due to pseudoenhancement and partial volume averaging; consider MRI for problem-solving 2
• Do not skip chest imaging – metastatic evaluation is essential even for small, incidentally discovered masses 2
• Central renal masses may suggest urothelial carcinoma rather than renal cell carcinoma; consider urine cytology or ureteroscopy 2

Counseling and Multidisciplinary Approach

A urologist should lead the counseling process and consider all management strategies including partial nephrectomy, radical nephrectomy, thermal ablation, and active surveillance. 1 A multidisciplinary team should be included when necessary based on patient-specific factors. 1

Male sex and tumor size are the most reliable predictors of malignancy, though degree and pattern of enhancement and tumor complexity help estimate malignancy risk, generate differential diagnoses, and guide intervention selection. 1