Abdominal Ultrasound is the Most Appropriate Initial Diagnostic Assessment
In a boy presenting with shortness of breath, hematuria, a large abdominal mass, and decreased lung perfusion, abdominal ultrasound should be performed first to characterize the renal mass, followed urgently by chest CT for staging. This clinical presentation is highly concerning for Wilms tumor with pulmonary metastases 1, 2.
Clinical Reasoning
Why This Presentation Suggests Wilms Tumor
The constellation of findings points strongly toward a renal malignancy with metastatic disease:
- Large abdominal mass with hematuria in a child is the classic presentation of Wilms tumor, which typically arises from the kidney 1, 2, 3
- Decreased lung perfusion on auscultation suggests pulmonary metastases, as the lung is the most common site of metastasis for renal tumors 4
- Wilms tumor commonly presents as an abdominal mass (96.7% of cases) with hematuria occurring in approximately 26.7% of patients 5
The Correct Diagnostic Sequence
Step 1: Abdominal Ultrasound (Answer B)
The American College of Radiology explicitly recommends ultrasound as the initial imaging modality for evaluating abdominal masses in children with hematuria 4, 1, 2. This approach is critical because:
- Ultrasound confirms the renal origin of the mass and differentiates it from other abdominal pathology 2
- It assesses tumor size, extent, involvement of the renal vein or inferior vena cava, and contralateral kidney status 2
- It is highly sensitive, readily available, requires no ionizing radiation, and can be performed without anesthesia or contrast 1
- The abdominal mass must be characterized first to guide subsequent management 1
Step 2: Chest CT (Not the Initial Test)
While chest CT is essential and should follow urgently after ultrasound confirmation, it should not precede the abdominal evaluation 1, 2. The American College of Radiology specifically advises against proceeding directly to CT without ultrasound confirmation of renal origin, as ultrasound may reveal the mass is not renal, changing the entire diagnostic approach 2.
Common Pitfalls to Avoid
- Do not skip ultrasound and go directly to lung CT: Even though pulmonary findings are present, the primary tumor must be characterized first 1, 2
- Do not delay imaging: Urgent evaluation with ultrasound is necessary in a child with an abdominal mass and hematuria, as delayed diagnosis can impact treatment outcomes 1
- Do not assume isolated hematuria requires no imaging: In the presence of an abdominal mass, this is a critical diagnostic scenario requiring immediate evaluation 1
Why Lung CT Alone is Inadequate
Performing lung CT first (Answer A) would be inappropriate because:
- It does not characterize the primary abdominal pathology 1, 2
- The treatment approach depends on confirming the renal origin and extent of the primary tumor 2
- Ultrasound provides essential information about bilateral kidney involvement, vascular invasion, and associated anomalies that directly impact surgical planning 1, 2