A 45-year-old man with chronic abdominal symptoms presents with abdominal pain, diarrhea, and weight loss.

Fig. 87.1 An axial CT image shows mild enhancement and thickening of terminal ileal (arrow) and cecum walls at the ileocecal junction with mild peri-inflammatory fat stranding.

Fig. 87.2 An axial CT image shows moderate, irregular wall thickening of the terminal ileum (arrow). The walls of inflamed bowel loops have a stratified appearance and present mild enhancement after intravenous administration of contrast medium. There is prominence of mesenteric vessels surrounding the inflamed bowel.

Crohn disease (regional enteritis/terminal ileitis/granulomatous ileocolitis)

• Infectious enterocolitis, including tuberculosis
  
• Eosinophilic enteritis
  
• Radiation enteritis
  
• Behçet disease

• Ulcerative colitis
  
• Diverticulitis
  
• Acute appendicitis, which can be mimicked by acute ileitis
  
• Carcinoma or lymphoma

Crohn disease is a chronic granulomatous inflammatory condition of unknown etiology, occurring in multiple discontiguous sites of the gastrointestinal tract. Lesions may occur anywhere from the mouth to the anus but are mostly encountered in the small bowel, especially the terminal ileum (in 80%), colon (in 70%), and, less commonly, duodenum (in 20%). The small and large bowels are frequently both involved. Incidence is higher among Caucasians in their 2nd to 3rd decade, and women are slightly more affected than men. The most typical pathologic feature is the involvement of all layers of the diseased bowel.