Large bowel obstruction Quiz: Ace Your Exams

A 25-year-old man presents to the emergency department with abdominal pain, bloating, nausea, and obstipation. He was recently treated in the urgent care for an upper respiratory infection that led to an asthma exacerbation. Past medical history is significant for asthma and moderate ulcerative colitis. The patient is on maintenance medication for ulcerative colitis which he occasionally skips. In the past he has used loperamide as needed for mild diarrhea. He has not experienced any recent fevers, or diarrhea with blood or mucus, but has had occasional constipation over the past few months. Temperature is 36.8 °C (98.2 °F), pulse is 88/min, blood pressure is 112/76 mmHg, respirations are 16/min, and oxygen saturation is 100% on room air. On examination, the patient’s abdomen is distended with mild tenderness to palpation diffusely. There is no evidence of guarding or rebound tenderness. Abdominal radiograph is obtained and shown below. Which of the following is the most likely underlying cause of his presentation?
 
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