Appendix not seen on CT is occasionally encountered when the appendix can not be visualized on the CT. This is especially important when there is a clinical suspicion for appendicitis. The appendix is usually seen as a worm like structure at the base of the cecum or start of the colon. Occasionally, the structure is not seen on CT. Most commonly in my experience this is because there is a lot of crowding in the area from bowel loops or the patient is thin and has little fat to spread structures apart.
The radiologist looks for the appendix in it’s expected location at the base of the cecum. Appendicitis usually has a characteristic appearance on CT. You see a dilated appendix which is filled with fluid, thickened and surrounded by dirty fat or inflammatory changes. Sometimes you may only see one of the findings when it’s early, or fluid and perforation when the appendix bursts.
Without seeing the appendix directly, it can be impossible to exclude appendicitis, especially early appendicitis where you may not see inflammation surrounding the appendix. In these cases, the radiologist will often state that appendix not seen and appendicitis is not excluded. Sometimes radiologists will say that there are no secondary findings of appendicitis. This means that the radiologist does not see the appendix, but also does not see any inflammation in the fat in it’s expected location.
Not seeing the appendix on CT presents a challenge because appendicitis is a diagnosis that often can not wait. A patient with early appendicitis should ideally be operated on, and at worst observed in the hospital with a surgeon on board. Therefore, not seeing the appendix on CT presents a difficult situation.
The clinical doctors already have a certain suspicion for appendicitis based on the clinical and laboratory presentation. Although I have seen many cases where the suspicion was low, or an alternate diagnosis was considered that turned out to be acute appendicitis.
One of the things that helps the clinical doctors is when the radiologist states that he does not see the appendix, but there are no secondary findings. This means that the appendix is not seen, but there are no inflammatory changes in it’s expected location. The clinician can then use his judgement to decide what to do next.
The patient can be sent home if suspicion is low with clear instructions to return if symptoms get worst. Alternatively, the patient may be admitted for observation and to see how he does. Another CT with oral contrast can be done to better define the bowel and appendix. In some cases, the patient will be taken to the operating room for treatment given the high clinical suspicion for acute appendicitis. Usually a surgeon will direct care at this point.