This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal Radiology, Subject name: Radiology
Mexican hat sign is seen in 
Select and explain. 
A. Sigmoid volvulus, B. Midgut volvulus, C. Sessile colonic polyp, D. Pedunculated polyp
D: Pedunculated polyp
Answer: D: Pedunculated polyp 
Explanation: Pedunculated colonic polyps form the "Mexican hat sign." The Mexican hat sign is formed by the appearance of 2 concentric rings; the outer ring represents the "en face" visualization of barium coating the surface of the head of a pedunculated polyp, while the inner ring represents a meniscus of barium surrounding the stalk of the polyp visualized through the head