This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Abdominal Ultra-sonography in a 3 year old boy shows a solid well circumscribed hypo-echoic renal mass. Most likely diagnosis is: 
Select and explain. 
A. Wilm's tumor, B. Renal cell carcinoma, C. Mesoblastic nephroma, D. Oncocytoma
A: Wilm's tumor
Answer: A: Wilm's tumor 
Explanation: Nephroblastoma (Wilm's tumour) is the commonest renal tumour in children and on USG appears a well circumscribed hypo echoic, solid mass. Ref: Differential Diagnosis in Abdominal Ultrasound By Bisset, 3rd Edition, 2008, Preview