A 3-year-old girl presents to the pediatric outpatient clinic with her mother, who noticed a firm, non-tender abdominal mass while bathing the child 2 weeks ago. The child is asymptomatic, with no fever, vomiting, or weight loss. Vital signs are normal. On examination, a 5 cm fixed mass is palpable in the left flank, crossing the midline. Hemoglobin is 10.2 g/dL (mild anemia), and urinalysis is normal. Abdominal ultrasound shows a heterogeneous left renal mass with areas of necrosis. Which of the following is the most appropriate next step in management?

Explanation

## Clinical Diagnosis: Wilms Tumor (Nephroblastoma) **Key Point:** This is a classic presentation of Wilms tumor—a unilateral renal mass in a young child (peak age 2–5 years) discovered incidentally during routine care. The heterogeneous appearance with necrosis on ultrasound is typical. ### Management Algorithm for Wilms Tumor ```mermaid flowchart TD A[Suspected Wilms Tumor]:::outcome --> B[Staging CT/MRI abdomen + chest]:::action B --> C{Metastases present?}:::decision C -->|No| D[Preoperative chemotherapy]:::action C -->|Yes| E[Preoperative chemotherapy<br/>+ radiation planning]:::action D --> F[Reassess with imaging]:::action E --> F F --> G[Delayed nephrectomy]:::action G --> H[Postoperative chemotherapy<br/>based on stage/histology]:::action ``` ### Why Chemotherapy Before Surgery? 1. **Reduces tumor burden** → facilitates complete resection and reduces spillage risk 2. **Assesses chemosensitivity** → guides postoperative therapy intensity 3. **Improves overall survival** → COG/SIOP protocols show superior outcomes with neoadjuvant therapy 4. **Allows time for staging** → full metastatic workup before definitive surgery **High-Yield:** The standard of care (COG protocol in North America, SIOP in Europe) is **preoperative chemotherapy followed by delayed nephrectomy**, NOT immediate surgery. This is a common exam trap. ### Staging Investigations Required | Investigation | Purpose | | --- | --- | | Contrast-enhanced CT abdomen/pelvis | Assess tumor extent, renal vein/IVC involvement, contralateral kidney | | Chest CT or CXR | Detect pulmonary metastases (most common site) | | Renal function tests | Baseline before chemotherapy | | Cardiac echo (if doxorubicin planned) | Baseline ejection fraction | **Clinical Pearl:** Wilms tumor is bilateral in ~5–10% of cases; imaging of the contralateral kidney is mandatory before any surgical decision. ### Why Not the Other Options? - **Immediate nephrectomy:** Outdated approach; increases morbidity and reduces cure rates compared to neoadjuvant chemotherapy. - **Observation:** Wilms tumor is rapidly progressive; delay risks metastatic spread and worse prognosis. - **Needle biopsy:** Contraindicated—risk of tumor spillage and seeding; diagnosis is made by imaging + clinical context.