What is the most important investigation for a 3-year-old child presenting with poor feeding, hematuria, a large abdominal mass, and decreased air entry on chest examination?

Most Important Investigation: Abdominal Ultrasound

Abdominal ultrasound is the most important initial investigation for this 3-year-old child presenting with poor feeding, hematuria, a large abdominal mass, and decreased air entry on chest examination, as this clinical constellation strongly suggests Wilms tumor with pulmonary metastases.

Clinical Reasoning

Primary Concern: Wilms Tumor

• The combination of abdominal mass and hematuria in a 3-year-old is highly characteristic of Wilms tumor, which commonly presents as an asymptomatic abdominal mass, often accompanied by hematuria when involving the collecting system 1, 2
• The mean age at diagnosis for Wilms tumor is approximately 36 months (3 years), making this patient's age典型 for this malignancy 3
• Decreased air entry in multiple chest areas strongly suggests pulmonary metastases, which are common in advanced Wilms tumor 3

Why Abdominal Ultrasound First

Ultrasound is the appropriate initial imaging modality for evaluating abdominal masses in children with hematuria 4:

• Ultrasound displays kidney anatomy, size, and position effectively and can screen for structural lesions causing hematuria 4
• It is highly sensitive, readily available, requires no ionizing radiation, and can be performed without anesthesia or contrast 5, 6
• Ultrasound has a definite role in investigating suspected upper gastrointestinal and renal disease in children and should be considered as the initial imaging modality 6
• It can detect parenchymal changes of abdominal organs and identify masses, though definitive diagnosis requires detailed radiologic assessment 4

Staging Requires Additional Imaging

While abdominal ultrasound is the most important initial investigation:

• Chest CT will be necessary to fully evaluate the pulmonary findings and stage the disease, as lung metastases are common in Wilms tumor 3
• However, chest CT should follow abdominal ultrasound in the diagnostic algorithm, not precede it
• The abdominal mass must be characterized first to guide subsequent management

Role of Bone Marrow Aspiration

Bone marrow aspiration is not indicated for typical Wilms tumor:

• Wilms tumor does not typically metastasize to bone marrow
• Bone marrow aspiration would be considered for clear cell sarcoma of the kidney, which has a predilection for skeletal metastases (particularly skull) 2
• However, this represents only a small fraction of pediatric renal tumors and is not the initial investigation

Clinical Pitfalls to Avoid

• Do not delay imaging in a child with an abdominal mass and hematuria—this requires urgent evaluation 4
• Do not assume isolated hematuria requires no imaging; the presence of an abdominal mass fundamentally changes the clinical scenario and mandates immediate ultrasound 4
• Do not proceed directly to CT without ultrasound first, as this exposes the child to unnecessary radiation when ultrasound can provide the critical initial diagnostic information 5, 6
• Recognize that poor feeding and constitutional symptoms in this context suggest advanced disease requiring expedited workup 3

Expected Ultrasound Findings

If Wilms tumor is present, ultrasound will demonstrate:

• A large renal mass (average tumor weight 635-899g) 2
• Possible involvement of the collecting system explaining the hematuria 1
• Assessment of the contralateral kidney 4
• Evaluation for inferior vena cava involvement