What is the most appropriate next diagnostic test for a child with a left flank abdominal mass and ultrasound findings of a mass with internal calcification?

CT with IV Contrast is the Most Appropriate Next Test

For a child with a left flank abdominal mass and ultrasound-confirmed internal calcification, CT with IV contrast is the most appropriate next diagnostic test before considering biopsy. 1

Rationale for CT as the Optimal Next Step

CT is specifically recommended by the American College of Radiology for deep or nonsuperficial masses in the flank region, where the complex anatomy limits the utility of other imaging modalities. 1 The key advantages include:

• Superior characterization of calcification patterns: CT is the optimal imaging method to distinguish between ossification and calcification, and can identify characteristic mineralization patterns that may be diagnostic. 1

• Multiplanar capability: CT is ideally suited to depict the character and interface of soft-tissue masses, particularly in assessing relationships with adjacent structures—critical information for surgical planning. 1

• Detection of zonal mineralization patterns: CT can detect the zonal pattern of mineralization essential for specific diagnoses, patterns that cannot be adequately characterized by ultrasound or other modalities. 1

Why Not MRI First?

MRI has inherent limitations in identifying and characterizing mineralization, which significantly limits its use when calcification is a prominent feature of the mass. 1 The American College of Radiology states that literature does not support MRI as the initial examination for a soft-tissue mass, particularly when calcification needs characterization. 1

However, MRI should be obtained after CT if the CT findings are indeterminate or suggest malignancy, as MRI provides superior soft-tissue characterization that can further narrow the differential diagnosis before proceeding to biopsy. 1

Why Not Proceed Directly to Biopsy?

Adequate imaging characterization must precede biopsy to guide the procedure and avoid complications. 1 CT provides essential information about:

• Mass extent and margins
• Relationship to adjacent structures (vessels, organs, spine)
• Calcification pattern and distribution
• Whether biopsy is even necessary (some calcification patterns are diagnostic)
• The safest approach if biopsy is required 1

Recommended Diagnostic Algorithm

1. Obtain contrast-enhanced CT of the abdomen to characterize the mass, its calcification pattern, and relationship to adjacent structures. 1

2. If CT findings are indeterminate or suggest malignancy, proceed to MRI for superior soft-tissue characterization before biopsy. 1

3. If imaging remains nondiagnostic and clinical concern persists, refer for image-guided biopsy with multidisciplinary input. 1

Technical Considerations

• Use a complete CT protocol with precontrast images: Distinguishing subtle calcification from enhancement may require precontrast images, so a complete protocol should be obtained. 1

• IV contrast is essential: Contrast enhancement allows assessment of the solid versus cystic nature of components, vascularity, and relationship to major vessels. 1, 2

Common Pitfalls to Avoid

• Proceeding to biopsy without adequate imaging: This can result in sampling error, complications from inadvertent vascular injury, or unnecessary procedures when imaging findings are diagnostic. 1

• Relying solely on ultrasound: While ultrasound confirmed the mass and calcification, it has limited ability to characterize deep masses in the flank and cannot adequately assess the relationship to retroperitoneal structures. 1, 3

• Ordering MRI first when calcification is prominent: This wastes time and resources, as MRI cannot adequately characterize mineralization. 1