Difficulties in the diagnosis of appendicitis: review of CT and US images.

To determine the reasons for missing a distended appendix, we discuss cases of acute appendicitis in which either or both computed tomography (CT) and/or ultrasonography (US) initially failed to detect distended appendix. In some cases, distended appendices that were undetected on US were easily detected by CT, and vice versa. Failure to detect a distended appendix does not always eliminate the possibility of acute appendicitis.