What is the next step to establish the diagnosis in a 3‑year‑old child with an incidentally discovered hard, non‑mobile flank mass containing internal calcifications on plain radiograph?

CT Abdomen is the Next Step

In a 3-year-old child with a hard, non-mobile flank mass containing internal calcifications on plain radiograph, CT abdomen should be performed next to characterize the calcification pattern, evaluate the mass extent, and assess involvement of adjacent structures before any biopsy is considered. 1, 2

Rationale for CT as the Optimal Next Step

Superior Characterization of Calcification

• CT excels at detecting and characterizing mineralization patterns, which is essential for distinguishing between different pediatric abdominal masses such as neuroblastoma (which commonly calcifies), Wilms tumor (calcifies in 5-15% of cases), and soft-tissue sarcomas 1, 2
• CT can identify the specific pattern and distribution of calcification that may be pathognomonic for certain conditions, information that cannot be adequately obtained from plain radiographs alone 1, 2
• The multiplanar capability of CT is ideally suited to depict the interface between the soft-tissue mass and adjacent structures, assessing for cortical remodeling or invasion—critical information for surgical planning 1, 2

Essential Pre-Biopsy Imaging

• Adequate cross-sectional imaging must precede any biopsy attempt 3, 1, 2
• CT provides essential information about mass extent, relationship to adjacent structures, and calcification pattern that determines whether biopsy is necessary and guides the safest approach if it is required 1, 2
• The American College of Radiology emphasizes that staging studies should be obtained before biopsy to allow proper selection of the biopsy site and to avoid compromising future limb salvage or definitive surgery 3

Protocol Considerations

• Obtain noncontrast CT images first, as distinguishing subtle calcification from enhancement may be difficult or impossible without precontrast images 1, 2
• Add IV contrast to evaluate vascularity, tumor margins, and involvement of adjacent structures, particularly in anatomically complex regions like the flank 1, 2
• Ensure imaging includes the entire compartment to assess for local extension and relationship to adjacent structures 1

Why Not the Other Options?

MRI Abdomen

• While MRI provides excellent soft-tissue characterization, it has inherent limitations in identifying and characterizing mineralization, which is a prominent feature in this case 1, 2
• The American College of Radiology states that literature does not support MRI as the initial examination for a soft-tissue mass when calcification needs characterization 2
• MRI may be used as a complementary study after CT if additional soft-tissue characterization is needed, particularly for pre-operative evaluation 1

Biopsy of the Mass

• Performing biopsy before adequate cross-sectional imaging violates fundamental principles of orthopedic oncology and can compromise definitive treatment 3, 1, 2
• Biopsy should only be performed at a reference center by the surgeon who will carry out definitive resection or by a member of that team 3
• Invasive sampling is not generally the initial workup of indeterminate masses 1

Bone Marrow Aspiration

• Bone marrow aspiration would only be indicated after establishing the diagnosis and determining if the mass is a metastatic malignancy that requires staging
• This is premature without first characterizing the primary mass itself

Critical Pitfalls to Avoid

• Do not assume all flank masses with calcification are renal in origin—the differential is broad and includes neuroblastoma, Wilms tumor, soft-tissue sarcomas, myositis ossificans, and vascular malformations 1
• Do not perform biopsy before adequate imaging, as this can contaminate tissue planes and compromise surgical options 3, 1, 2
• Ensure referral to a specialized center if your institution cannot perform definitive diagnostic studies, as management of suspected pediatric abdominal malignancies requires multidisciplinary expertise 3, 1