A 2-year-old boy presents with an abdominal mass that crosses the midline on imaging. Histopathology shows small round blue cells arranged around central neuropil, as marked by **A** in the diagram. Urinary metabolites including homovanillic acid (HVA) and vanillylmandelic acid (VMA) are elevated. Which of the following best describes the origin of this tumor?

Explanation

## Why "Neural crest cells of the adrenal medulla or sympathetic chain" is right The Homer-Wright rosette pattern (marked **A**) is the pathognomonic histologic finding of neuroblastoma. Neuroblastoma arises from neural crest cells that form the adrenal medulla and sympathetic chain ganglia. The clinical presentation—abdominal mass crossing the midline in a 2-year-old with elevated urinary catecholamine metabolites (HVA and VMA)—is classic for neuroblastoma, the most common extracranial solid tumor of childhood. This embryologic origin directly explains both the tumor location and the biochemical abnormality. (Robbins 10e, Ch 10) ## Why each distractor is wrong - **Mesodermal remnants of the urogenital ridge**: This is the embryologic origin of Wilms tumor (nephroblastoma), not neuroblastoma. Wilms tumors do not typically cross the midline and do not produce catecholamine metabolites. - **Primitive metanephric blastema**: Again, this describes Wilms tumor histogenesis. The presence of Homer-Wright rosettes and elevated HVA/VMA excludes Wilms. - **Endodermal cells of the foregut**: This would be consistent with gastroenteropancreatic neuroendocrine tumors, which are rare in young children and do not present with the classic abdominal mass crossing the midline. **High-Yield:** Neuroblastoma = neural crest origin + adrenal/sympathetic location + Homer-Wright rosettes + catecholamine metabolites (HVA/VMA); Wilms = mesodermal origin + kidney-based + does NOT cross midline. [cite:Robbins 10e Ch 10]