One in every 2000 people may have their appendix removed because of appendicitis. However, the clinical differential diagnosis of appendicitis is often very difficult, and in some patients it is very difficult to confirm the diagnosis before surgery. Crohn’s disease is a chronic inflammatory disease of the intestine, with most lesions located at the end of the ileum near the appendix. Crohn’s disease is incurable for life and is characterized most by slow or even non-healing wounds. Therefore, patients with Crohn’s disease who undergo appendectomy may experience non-healing at the resection site, leading to the development of intestinal fistulas. Both appendicitis and Crohn’s disease are seen mostly in young people, and both may be present in combination, making the differential clinical diagnosis very difficult. In the past, Crohn’s disease was a rare and relatively “new” disease, the name of which was established only in the 1960s, and was generally not well understood by the medical community. With the increasing incidence of the disease, it has only gradually attracted the attention of the medical profession in the last decade. Therefore, it is necessary to draw attention to this disease. Acute ileitis misdiagnosed as acute appendicitis Sometimes a patient is proposed to be diagnosed with appendicitis and undergoes a caesarean section, but is found to have Crohn’s disease of the distal ileum (acute ileitis) intraoperatively. There are different views on the appropriate management in such cases, and the key question is whether to remove the appendix or not. Simonowitz, after summarizing 20 patients who underwent appendectomy in this situation, suggests that if the patient has abdominal pain for less than 1 week, there are few complications after appendectomy. If the patient’s symptoms lasted longer than 1 week, fistula or sinus tract formation occurred in 83% of cases after appendectomy, and not in the appendiceal stump, but in the terminal ileum. Most surgeons agree that the fistula originates in the ileum unless Crohn’s disease has involved the cecum. A case of intestinal fistula after appendectomy at an outside hospital (preoperative diagnosis of “appendicitis”) that I encountered 5 years ago was reported at Lahey Medical Center in the United States, where 36 cases of ileal Crohn’s disease were unexpectedly found intraoperatively after a dissection for suspected appendicitis. After early ileocolic resection, no further surgical resection was required in half of the cases, with a mean follow-up of 12 years. In contrast, 92% of the cases without early ileocolic resection would later require reoperative resection of the ileum due to some difficult problem or complication of Crohn’s disease. They concluded that the majority of patients who undergo dissection for appendicitis and are found to have Crohn’s disease require early ileocolic resection. The traditional concept of non-excisional surgery should be re-evaluated. Fat encapsulation: a basis for intraoperative determination of the presence or absence of Crohn’s disease It has also been argued that the surgeon may choose to perform an appendectomy if he is convinced that the appendix is normal; this would facilitate the differential diagnosis of abdominal pain later. In fact, right lower abdominal pain with signs of peritoneal irritation unrelated to Crohn’s disease is very rare. If this does occur, it is likely that there will be a long delay before surgical treatment is performed. The finding of terminal ileitis by the surgeon at the time of performing appendectomy should be of particular concern. This is easier said than done. This is because terminal ileitis should also be considered as a possibility of self-limiting ileitis caused by Yersinia or Campylobacter, which can heal spontaneously and does not require surgery. In summary, I believe that it is difficult to make an accurate judgment in the case of a proposed diagnosis of “appendicitis” but the possibility of Crohn’s disease is found unexpectedly during surgery, The basic clinical skills of history taking, clinical experience, making the necessary differential diagnosis, and adequate doctor-patient communication are still essential. Crohn’s disease confined to the appendix is a rare condition, and a case study in 1990 noted that: 1) it is common in the 20-30 age group; 2) the signs and symptoms resemble those of acute appendicitis; 3) abdominal masses are palpable in 27% of cases; and 4) the presence of similar symptoms in the past and a long history of the disease should alert the surgeon to the possibility of Crohn’s appendicitis. In another study, 12 cases of Crohn’s disease appendicitis were analyzed. 8 cases were treated surgically for appendicitis, 2 cases for appendiceal abscess, 1 case of suspected tubal abscess, and 1 case of ovarian cyst. Of the eight patients diagnosed with appendicitis, six underwent appendectomy and two underwent enlargement. No postoperative fecal fistula occurred in any of them. The median duration of follow-up was 14 years, and none of the patients developed further manifestations of Crohn’s disease. Thus, the prognosis is very good when Crohn’s disease is confined to the appendix.