This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: New Born Infants, Subject name: Pediatrics
A 3-week-old child presents with an abdominal mass. What is the most common cause of the presentation? 
Select and explain. 
A. Neuroblastoma, B. Wilms tumor, C. Multicystic dysplastic kidney, D. Distended bladder
C: Multicystic dysplastic kidney
Answer: C: Multicystic dysplastic kidney 
Explanation: c. Multicystic dysplastic kidney(Ref: Nelson's 20/e p 2555)Multicystic dysplastic kidney is the most common cause of an abdominal mass in the newborn, but the majority are nonpalpable at birth.