Diagnosis of Wilms Tumor in Children
Abdominal ultrasound is the optimal initial diagnostic tool for a child under 5 with a palpable abdominal mass suspected to be Wilms tumor, followed by CT or MRI for complete staging. 1
Initial Diagnostic Approach
Ultrasound is the first-line imaging modality because it is widely available, lacks ionizing radiation, can be performed without sedation, and has high sensitivity for detecting renal masses. 1 The ultrasound should:
- Confirm the renal origin of the mass 1
- Evaluate the inferior vena cava for tumor extension using Doppler 1
- Assess the bladder for additional lesions 1
- Examine the contralateral kidney for bilateral disease 1
Clinical Presentation Features
The most common presentation is an asymptomatic abdominal mass or swelling, often discovered incidentally by parents or during routine examination. 2 Key clinical features that suggest Wilms tumor include:
- A large mass arising from the kidney parenchyma that distorts the collecting system 3
- Age typically between 1-6 years, with peak incidence around 3-4 years 2, 4
- The mass is usually unilateral (85-90% of cases), though bilateral disease occurs in 4-13% 1, 5
Advanced Imaging for Staging
After ultrasound confirmation, proceed with CT or MRI with contrast for complete staging. 3 The choice between CT and MRI depends on specific clinical scenarios:
- MRI is preferred when evaluating bilateral tumors, detecting nephrogenic rests, and planning nephron-sparing surgery 1, 6
- Chest CT is mandatory for staging, as pulmonary metastases are the most common site of metastatic spread, occurring in 10-15% of cases at presentation 3
- Document tumor size, laterality, vascular involvement (tumor thrombus, vascular encasement), and infiltration of adjacent structures 1, 6
Laboratory Evaluation
While imaging is diagnostic, obtain baseline laboratory tests:
- Serum creatinine, hemoglobin, leukocyte and platelet counts 6
- These tests serve as prognostic indicators and baseline values for treatment monitoring 6
Role of Biopsy
The North American Children's Oncology Group (COG) recommends upfront nephrectomy for unilateral tumors without pre-operative biopsy, as biopsy risks tumor spillage and upstaging the disease, necessitating more intensive chemotherapy and radiation. 1 Biopsy should only be considered when:
- The renal origin is doubtful 7
- A pseudotumor is suspected 7
- Non-Wilms histology is anticipated based on imaging features 7
Differential Diagnosis Considerations
Distinguish Wilms tumor from other pediatric abdominal masses:
- Neuroblastoma typically arises from the adrenal gland or sympathetic chain, not from within the kidney itself, and is associated with elevated urinary catecholamines and bone/bone marrow involvement 1, 3
- Hepatoblastoma presents with elevated AFP levels and hepatic mass on ultrasound 1
- Rhabdomyosarcoma rarely presents as a primary renal mass 3
Genetic Testing Indications
Pursue genetic testing in patients with bilateral tumors, as they often represent genetic predisposition syndromes. 1 Universal genetic testing should include:
- Methylation and copy-number analysis of chromosome 11p15.5 1
- Sequencing and copy-number analysis of WT1 1
- Testing for common predisposition genes (TRIM28, REST, CTR9, DIS3L2, DICER1) 5
Children with predisposing syndromes (WT1 mutations, Beckwith-Wiedemann syndrome, WAGR syndrome, Denys-Drash syndrome, DICER1 syndrome) require specific surveillance protocols. 5, 3
Critical Pitfalls to Avoid
- Do not miss bilateral disease by failing to carefully evaluate the contralateral kidney on initial imaging 1
- Do not perform biopsy on typical unilateral cases, as this increases risk of tumor spillage and upstaging 1
- Do not delay referral to specialized pediatric oncology centers, as all suspected malignant abdominal masses in children require multidisciplinary expertise 3
- Do not skip chest CT, as it is the most sensitive approach for detecting pulmonary metastases 6, 3