This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oesophagus, Subject name: Surgery
[{'content': 'Bent inner tube sign is seen in \nSelect and explain. \nA. Volvulus, B. Intussusception, C. Intestinal obstruction, D. Gastric antral vascular ectasia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) VolvulusRef: Manipal Manual of surgery, 4th ed./739* In sigmoid volvulus, the X ray abdomen erect shows hugely dilated sigmoid loop called bent inner tube sign.* Acute sigmoid volvulus presents as intestinal obstruction and starts after straining at stool. It occurs in anti-clockwise direction and after one and a half turns, the entire loop becomes gangrenous.* The percussion note on the abdomen shall be tympanitic note.', 'role': 'assistant'}]