A 4-year-old boy from rural Maharashtra presents with his mother to the pediatric outpatient clinic with a 2-month history of progressive abdominal distension and a palpable mass in the left flank. On examination, the mass is firm, non-tender, and does not cross the midline. Vital signs are normal. Abdominal ultrasound reveals a large heterogeneous mass arising from the left kidney with areas of cystic change. Serum alpha-fetoprotein (AFP) is normal; urinary catecholamine metabolites (VMA and HVA) are normal. 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. ### Diagnostic Reasoning | Feature | Wilms Tumor | Neuroblastoma | RCC | Mesoblastic Nephroma | |---------|------------|---------------|-----|---------------------| | **Age of onset** | 2–5 years | < 5 years (often < 2) | Older children | < 2 years | | **Origin** | Kidney (intrarenal) | Adrenal/sympathetic chain (extrarenal) | Kidney (older age) | Kidney (congenital) | | **Catecholamine markers** | Normal | Elevated VMA/HVA | Normal | Normal | | **AFP** | Normal | Normal | Normal | Normal | | **Presentation** | Abdominal mass, distension | Mass + systemic symptoms (fever, weight loss) | Hematuria (older) | Prenatal detection | | **Imaging: Mass location** | Intrarenal, heterogeneous | Extrarenal, paraspinal | Renal cortex | Intrarenal | ### Why This Case Points to Wilms Tumor 1. **Age 4 years** — peak incidence of Wilms tumor (2–5 years) 2. **Intrarenal mass** — ultrasound shows mass arising FROM the kidney 3. **Normal catecholamine metabolites** — rules out neuroblastoma (which would show elevated VMA/HVA in ~90% of cases) 4. **Normal AFP** — consistent with Wilms tumor (AFP is a hepatoblastoma marker, not Wilms) 5. **Non-crossing midline** — typical of unilateral renal tumor; neuroblastoma can cross midline if paraspinal **High-Yield:** The **normal urinary catecholamine metabolites** is the key discriminator here. Neuroblastoma arises from neural crest cells and secretes catecholamines; Wilms tumor does not. ### Associated Syndromes (WAGR & Denys-Drash) **Mnemonic: WAGR** — **W**ilms, **A**niridia, **G**enitourinary anomalies, **R**etardation (intellectual disability) **Denys-Drash syndrome:** Wilms tumor + pseudohermaphroditism + progressive nephropathy (WT1 gene mutation) ### Management Principles 1. **Imaging:** CT/MRI abdomen and pelvis for staging, chest imaging for metastases 2. **Staging:** TNM staging (Stage I–V); unilateral vs. bilateral 3. **Treatment:** Multimodal (chemotherapy + surgery ± radiotherapy) depending on stage and histology 4. **Prognosis:** Overall 5-year survival ~90% (favorable histology) to 50% (anaplastic) **Clinical Pearl:** Always examine for aniridia, cryptorchidism, and hemihypertrophy in a child with a renal mass — these are associated with Wilms tumor and warrant screening with ultrasound every 3 months until age 7. [cite:Park 26e Ch 12]