USMLE Step 1 Question Bank

A 56-year-old man comes to his primary care physician because of 4 months of intermittent crampy abdominal pain and episodic bloating that occur every 1-2 weeks and last several hours. During two episodes, he noticed passage of dark red, mucus-streaked stool. He reports a 6-kg (13-lb) unintentional weight loss and early satiety but no fever. He had a screening colonoscopy 3 years ago that showed only diverticulosis. Temperature is 36.9 C (98.4 F), blood pressure is 128/76 mm Hg, pulse is 82/min, and respirations are 14/min. Abdominal examination between episodes shows mild periumbilical tenderness without guarding or rebound; no masses are palpated. Hemoglobin is 10.8 g/dL, and mean corpuscular volume is 78 fL. CT enterography obtained after another painful episode shows a short segment of proximal small bowel telescoped into distal bowel with a 3-cm intraluminal mass at the apex of the lesion. Which of the following best explains the pathophysiology underlying this patient's recurrent episodes?