False ileitis: appendiceal phlegmon with fistulization to the terminal ileum mimicking Crohn's disease.

Appendiceal disease may occasionally mimic inflammatory bowel disease (IBD), particularly when inflammation involves the terminal ileum and cecum. We report a 23-year-old man presenting with right lower quadrant abdominal pain and diarrhea, whose initial imaging findings suggested inflammatory or infectious ileocolitis, with IBD remaining in the differential diagnosis. Ileocolonoscopy revealed fibrinopurulent discharge from an inflamed appendiceal orifice and a focal inflammatory lesion in an otherwise normal terminal ileum, suggestive of fistulization from an adjacent appendiceal process. Subsequent imaging and laparoscopic surgery confirmed complicated acute appendicitis with an appendiceal phlegmon involving the terminal ileum and ileal fistulization. Histopathological examination confirmed acute gangrenous appendicitis. This case highlights the potential of appendiceal disease to mimic IBD and the diagnostic value of recognizing focal ileal abnormalities associated with appendiceal inflammatory findings.