## Why option 1 is correct The tumor marked **B** is neuroblastoma, which arises from neural crest-derived cells of the adrenal medulla or sympathetic chain. It is the **most common extracranial solid tumor of childhood**, with a median age of presentation around 2 years. The clinical presentation in this case—midline-crossing mass with stippled calcifications, elevated urinary HVA/VMA, and Homer-Wright rosettes on histology—are pathognomonic for neuroblastoma. The embryological origin from neural crest cells distinguishes it from Wilms tumor (which arises from metanephric mesenchyme) and explains its catecholamine-secreting phenotype (Robbins 10e Ch 10; Nelson 21e Ch 522). ## Why each distractor is wrong - **Option 2**: Describes Wilms tumor (nephroblastoma), which arises from metanephric mesenchyme, is intrarenal (does NOT cross midline), and has peak incidence at 2–5 years. The clinical presentation here (midline crossing, calcifications, elevated catecholamine metabolites) is inconsistent with Wilms. - **Option 3**: Carotid body tumors are paragangliomas arising from chemoreceptor tissue, not neural crest cells of the adrenal medulla. They present as neck masses and are extremely rare in young children; they do not produce the urinary metabolite pattern seen here. - **Option 4**: Ectopic adrenal rest tumors are rare and typically present later in childhood with endocrine manifestations (hypertension, hypokalemia from aldosterone excess). They do not explain the elevated HVA/VMA or the typical age of presentation (~2 years). **High-Yield:** Neuroblastoma = neural crest origin (adrenal medulla/sympathetic chain), crosses midline, calcified, elevated HVA/VMA, Homer-Wright rosettes, age ~2 years. Wilms = metanephric mesenchyme origin, intrarenal, does NOT cross midline, age 2–5 years, triphasic histology. [cite: Robbins 10e Ch 10; Nelson 21e Ch 522]
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