During an operation for presumed appendicitis, the patient appendix is found to be markedly thickened and feels rubbery to firm. The serosa is edematous and inflamed and the mesentery is thickened with fat growing about the bowel circumference. Most likely diagnosis

Crohn's disease can present acutely, and when it involves the terminal ileum may clinically resemble appendicitis. The bowel in this patient has the characteristic gross findings and inflammatory changes of Crohn's disease including the "creeping fat" within the mesentery. Meckel's diveiculitis can mimic appendicitis but it presents as an inflammatory phlegmon located approximately 50 cm (2 feet) from the ileocecal varve and does not have the bowel changes seen in this patient. Ulcerative colitis is usually confined to the large bowel and, although it may occasionally be associated with inflammatory changes of the ileal mucosa (backwash ieitis), it is generally not associated with full- thickness changes described above. Ileal carcinoid would present as a mass in the ileum and would not be associated the inflammatory changes seen in this patient.