<prompt> Most common abdominal mass in children:HydronephrosisWilms tumorNeuroblastomaRhabdomyosarcoma  <response>: c. NeuroblastomaRef: Nelsons 20e p 2464-2466, Ghai 8e 617-618Neuroblastoma is the most common extracranial solid tumor in childrenLocalized Neuroblastoma can manifest as an asymptomatic mass or can cause symptoms because of the mass itself, including spinal cord compression, bowel obstruction superior vena cava syndrome.Note: Both Neuroblastoma Wilms tumor can present as abdominal mass in children but Neuroblastoma is more common than Wilms tumor, so it is the better answer to this question 