A 2-year-old girl from rural India presents with a firm, non-tender abdominal mass in the left upper quadrant. Her parents report she has been irritable and losing weight over the past 2 months. Ultrasound shows a heterogeneous mass arising from the adrenal gland with areas of calcification. Which is the most appropriate investigation to confirm the diagnosis and assess for metastatic disease?

Explanation

## Investigation of Choice for Neuroblastoma **Key Point:** MIBG scintigraphy (metaiodobenzylguanidine scan) is the gold standard imaging modality for diagnosis, staging, and detection of metastatic neuroblastoma. It is superior to anatomical imaging for identifying disease extent. ### Why MIBG Scintigraphy is Optimal 1. **Mechanism**: MIBG is a noradrenaline analog that is selectively taken up by catecholamine-secreting neural crest tumors (neuroblastoma, pheochromocytoma). 2. **Diagnostic yield**: Detects primary tumor and **all sites of metastatic disease** (bone, bone marrow, liver, lymph nodes, soft tissue). 3. **Staging accuracy**: MIBG scan is more sensitive than skeletal scintigraphy for bone metastases and detects bone marrow involvement. 4. **Prognostic value**: MIBG avidity correlates with tumor biology and treatment response. ### Diagnostic and Staging Workup for Neuroblastoma | Investigation | Purpose | Timing | |---|---|---| | **MIBG scintigraphy** | Diagnosis + metastatic staging | Baseline (gold standard) | | **CT/MRI abdomen** | Define local anatomy, assess resectability | Baseline + pre-operative | | **Chest CT** | Detect pulmonary/mediastinal involvement | Baseline | | **Bone marrow aspiration/biopsy** | Assess marrow involvement | Baseline (if MIBG positive) | | **Urine catecholamines/metanephrines** | Biochemical confirmation (elevated in >90%) | Baseline | | **Serum NSE, ferritin, LDH** | Prognostic markers | Baseline | **High-Yield:** Neuroblastoma arises from neural crest cells of the sympathetic nervous system. ~90% of cases present with elevated urinary catecholamines or metanephrines, but these are **markers, not diagnostic tests**. MIBG scan is required for definitive diagnosis and staging. **Mnemonic:** **MIBG = Metastasis Imaging By Guanethidine analog** — it finds all sites of disease. **Clinical Pearl:** Neuroblastoma has the highest propensity for spontaneous regression among pediatric malignancies, especially in infants <18 months (stage 4S). MIBG scan helps identify these favorable-risk cases. [cite:Park 26e Ch 13]