This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Inflammatory bowel disease, Subject name: Surgery
A 28-year-old man complains of abdominal pain and fever. The physician orders an abdominal CT scan which reveals inflammation of the large bowel. He is worked-up for inflammatory bowel disease and is diagnosed to have Crohn disease. What is the most common indication for surgery in such patients? 
Select and explain. 
A. Massive bleeding, B. Fistulas, C. Toxic megacolon, D. Malignancy
B: Fistulas
Answer: B: Fistulas 
Explanation: Fistulas formed between the large bowel and other segments of intestine, the bladder, the urethra, the vagina or the skin, are the most common indication for surgery in patients of Crohn's disease. Other options like massive bleeding, toxic megacolon, malignancy are also indications for surgery in inflammatory bowel disease.