This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: GIT and hepatobiliary system, Subject name: Radiology
Double track sign is seen in - 
Select and explain. 
A. Duodenal atresia, B. CHPS, C. Gastric ulcer, D. Achalasia
B: CHPS
Answer: B: CHPS 
Explanation: On upper gastrointestinal fluoroscopy: * delayed gastric emptying * peristaltic waves (caterpillar sign) * elongated pylorus with a narrow lumen (string sign) which may appear duplicated due to puckering of the mucosa (double-track sign) * the pylorus indents the contrast-filled antrum (shoulder sign) or base of the duodenal bulb (mushroom sign) the entrance to the pylorus may be beak-shaped (beak sign)