A 25-year-old man comes to the hospital due to worsening abdominal pain, distension, and nausea and vomiting for 3 days. He has a 4-year history of recurrent abdominal pain associated with diarrhea, low-grade fever, and easy fatigability. The symptoms usually occur after stress and resolve spontaneously in a few days. However, this time, the patient's symptoms persisted and worsened. He has no other medical problems and takes no medications on a regular basis. Temperature is 38.2 C (100.8 F), blood pressure is 110/70 mm Hg, pulse is 104/min, and respirations are 16/min. BMI is 19 kg/m². Examination shows a tender mass in the right lower quadrant of the abdomen. Imaging is consistent with small-bowel obstruction. Laparotomy reveals that the abdominal mass is composed of inflamed small bowel, adherent and indurated mesentery, and enlarged abdominal lymph nodes. The affected region of the small bowel is resected. Which of the following is most likely to be seen on histologic examination of this patient's intestine?

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11ec160b_3952_9ee6_9249_2bde7f1c203e_MD0001_00 This patient with recurrent abdominal pain and diarrhea likely has Crohn disease (CD) complicated by small-bowel obstruction. CD is an inflammatory bowel disease that occurs most commonly in young adults. It typically presents as recurrent episodes of abdominal pain associated with diarrhea, low-grade fevers, and fatigue; symptoms may worsen during periods of stress. The inflammation can affect any part of the gastrointestinal tract from the mouth to the anus and is typically patchy with interspersed areas of normal bowel (skip lesions). CD is characterized by transmural inflammation (all layers of the bowel wall are involved), which predisposes to several complications: Strictures occur as a result of bowel wall edema, fibrosis, and hypertrophy (thickening) of the muscularis mucosae, which narrows the intestinal lumen. This can progress to bowel obstruction. Fistulas occur when ulcers penetrate the entire thickness of the intestinal wall, leading to a sinus tract that communicates between multiple organs (eg, enterovesicular, enterovaginal, enteroenteric). Abscesses form when sinus tracts become walled off. They can also perforate, leading to diffuse peritonitis. (Choice A) Caseating granulomas are typically seen in multiple infectious processes, most notably tuberculosis (TB). Abdominal TB can present with abdominal pain, fevers, and occasional obstruction; however, symptoms are unlikely to spontaneously wax and wane, and evidence of TB is often present in other sites (eg, hemoptysis with pulmonary TB). CD is associated with noncaseating, rather than caseating, granulomas. (Choice B) Flask-shaped ulcers in the cecum and colon are seen in Entamoeba histolytica infection, which occurs more commonly in developing countries and presents with bloody diarrhea. Severe cases can cause fulminant colitis with bowel necrosis, but obstruction is uncommon. (Choice C) Ulcerative colitis is an inflammatory bowel disease that involves only the mucosa and submucosa. Inflammation involves contiguous areas of the colon only, and the small bowel is not involved. Due to the superficial nature of the inflammation, strictures and fistulas are not seen. (Choice D) Pseudomembranes composed of fibrin and inflammatory debris are seen with Clostridium difficile infection, which is typically associated with antibiotic use. Complications include toxic megacolon; however, C difficile does not cause obstruction and the small bowel is not typically involved. Educational objective: Crohn disease is characterized by patchy, transmural inflammation of the gastrointestinal tract. It can affect any part of the tract from the mouth to the anus. Complications include strictures (due to bowel wall edema, fibrosis, and thickening of the muscularis mucosae), fistulas (due to penetration of ulcers through the intestinal wall), and abscesses.

A 25-Year-Old Man Comes to the Hospital Due to Worsening