A 4-year-old boy from rural Maharashtra presents with his mother to the pediatric clinic with a 2-month history of abdominal distension and intermittent abdominal pain. On examination, a firm, non-tender, fixed mass is palpated in the left flank. Vital signs are normal. Abdominal ultrasound reveals a large heterogeneous mass arising from the left kidney with areas of necrosis and calcification. Serum electrolytes and renal function are normal. Urinalysis shows no hematuria. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Wilms Tumor ### Key Clinical Features **Key Point:** Wilms tumor is the most common renal malignancy in children, typically presenting between ages 2–5 years with abdominal mass and distension. This case presents the classic triad: 1. **Age:** 4 years (peak incidence 2–5 years) 2. **Presentation:** Abdominal mass (firm, fixed, flank location) with distension 3. **Imaging:** Heterogeneous renal mass with necrosis and calcification ### Distinguishing Features of Wilms Tumor | Feature | Wilms Tumor | Neuroblastoma | RCC | Mesoblastic Nephroma | |---------|-------------|---------------|-----|----------------------| | **Age of onset** | 2–5 years | < 5 years (often < 2) | Older children/adolescents | < 2 years | | **Origin** | Renal parenchyma | Adrenal/sympathetic chain | Renal tubules | Renal mesenchyme | | **Mass location** | Intrarenal | Extrarenal (adrenal/paravertebral) | Intrarenal | Intrarenal | | **Hematuria** | Rare (< 10%) | Absent | Common (40–50%) | Rare | | **Calcification** | 5–10% | Common (50–80%) | Rare | Rare | | **Associated syndromes** | WAGR, Denys-Drash, Beckwith-Wiedemann | Neurofibromatosis-1 | Sporadic | Sporadic | **High-Yield:** The absence of hematuria and presence of intrarenal heterogeneous mass with calcification strongly favor Wilms tumor over RCC. ### Pathophysiology Wilms tumor arises from **persistent metanephric blastema** — embryologic renal tissue that normally involutes by 36 weeks gestation. Mutations in **WT1** (chromosome 11p13) are found in ~90% of cases, and **WT2** (imprinting defects) in Beckwith-Wiedemann syndrome. ### Associated Syndromes (WAGR) **Mnemonic:** WAGR = **W**ilms, **A**niridia, **G**enitourinary anomalies, **R**etardation (intellectual disability) Other associations: - **Denys-Drash syndrome:** WT1 mutation, intersex development, progressive glomerulonephritis - **Beckwith-Wiedemann syndrome:** WT2 imprinting defect, macroglossia, hemihypertrophy, exomphalos ### Diagnostic Workup 1. **Imaging:** Abdominal ultrasound (first-line), then CT/MRI for staging 2. **Labs:** CBC, renal function, LDH (prognostic marker) 3. **Staging:** COG (Children's Oncology Group) system — Stage I (confined to kidney) to Stage V (bilateral) **Clinical Pearl:** Absence of hematuria in this case is actually reassuring for Wilms tumor (present in < 10%), whereas RCC commonly presents with hematuria. ### Management Multimodal therapy: - **Chemotherapy** (preoperative or postoperative) - **Surgical nephrectomy** with lymph node sampling - **Radiation therapy** (for advanced stages or unfavorable histology) **High-Yield:** Overall 5-year survival is ~90% with modern COG protocols; favorable histology has better prognosis than anaplastic histology.