<prompt> Which of these is the most common cause of a posterior mediastinum mass in children?RhabdomyomaDuplicated cyst of the esophagusThymomaNeuroblastoma  <response>: Ans. D. NeuroblastomaSeveral causes of posterior mediastinum mass in children are known; including neurogenic tumors most common cause, foregut cyst, germ cell tumors, lymphangiomas and lymphomas. Since the most common neurogenic tumor in children is neuroblastoma, it should be the correct answer. 