Acute appendicitis is one of the common causes of acute abdominal pain. Although the classical symptoms of acute appedicitis is periumbilical pain migrating to the right lower quadrant, the presentation is rarely typical and diagnostic errors are common resulting in both negative appendectomies or appendical perforations. This study systematically investigated the value of endoscopic retrograde appendicography in the diagnosis of acute appendicitis and showed a high diagnostic yield in patients with acute abdominal pain. Possibly more importantly was the ability to prevent unnecessary operations and preserve the normal appendix.
Previous studies have reported colonoscopy as a useful diagnostic method of acute appendicitis in the patients with atypical presentation of abdominal pain or with non-diagnostic imaging studies [6, 7]. Chang et al.  described the colonoscopic features of acute appendicitis, including hyperemia and bulging at the appendiceal orifice area with surrounding mucosal edema and drainage of pus from the appendcieal orifice. Our study confirms the value of these features. However, some patients with acute appendicitis did not have any of these colonoscopic features. In our study, although there were 17 patients (74%) with pus discharge from the appendiceal orifice, only 4 (23%) had spontaneous pus discharge. In 13 (77%) pus discharge only occurred after successful cannulation of appendiceal orifice. Moreover, one patient presented with normal mucosa around the area of appendiceal orifice which is consistent with the fact that in some patients the inflammatory changes may affect only the distal appendix . Thus, colonoscopy alone is unable to reliably predict which patients have an abnormal appendiceal lumen. In contrast, appendicography combined with colonoscopy allowed acquisition of clear images both of appendiceal orifice and lumen for providing more accurate diagnosis.
The advantage of endoscopic retrograde appendicography over traditional barium enema lies in higher success rate of filling appendix. The diagnosis of acute appendicitis by barium enema is mainly based on non-filling of the full appendix . However, 15–23% of normal appendices fail to fill [10, 11] such that failed filling of the appendix is not a reliable sign for acute appendicitis . On the contrary, with a remarkable success (91%) of filled appendix, endoscopic retrograde appendicography easily identified the presence of lumen dilatation, partial stenosis, lack of flexibility and intraluminal filling-defects and thus can reliably confirm the diagnosis of acute appendicitis.
Another advantage of endoscopic retrograde appendicograpgy over CT or US is that it provides radiological imaging of appendix with more objectivity, irrespective of shape and position of appendix within abdominal cavity. Although some studies have reported high sensitivity and specificity of CT and US [13–15], Wilson et al. described the equivocal rates of CT (28%) and US (75%) , which is consistent with the result of CT (33%) in the present study. However, the equivocal rate of US (12%) was lower than the previous study, maybe due to the small sample size. US is more operator dependent, relying both on the US technician and the interpretation by the radiologist. Even though CT is more objective, the diagnostic accuracy is also limited by technical and interpretative pitfalls due to the shape and position of appendix inside the abdomen . Actually, clinicians have reported potential negative appendectomy rates of 22% due to CT . Another reason for relative lower accuracy of CT and US in our study is that many cases underwent endoscopic retrograde appendicograpgy because of equivocal results of CT scan or US. Moreover, CT exposes the patient to more ionizing radiation than radiography and is associated with a risk of radiation-induced cancer.
Another advantage of endoscopic retrograde appendicography compared to CT or US lies in differential diagnosis of abdominal pain mimicking acute appendicitis. During the procedures, the endoscopist can visualize the entire colon or appendix and make histological diagnosis by biopsy. In the present study, endoscopic retrograde appendicography identified 4 patients with ileocecal lipoma, ulcerative colitis, colon and appendix carcinoma and typhlitis. However, further study is necessary to obtain a full comparison of the diagnostic accuracy of endoscopic retrograde appendicography, CT and US.
Previous studies have also reported that the patients with an atypical presentation were diagnosed as acute appendicitis using colonoscope . However, colonoscopy was not widely used for diagnosis of acute appendicitis, because the conventional wisdom is that colonoscope may aggravate abdominal pain and induce complications. However, there were no complications in this study. In contrast, the results showed that endoscopic retrograde appendicography can be safely performed on the patients with suspected acute uncomplicated appendicitis.
Endoscopic retrograde appendicography procedure can be performed in the outpatient department. Initially, we admitted patients after undergoing ERAT as this was a preliminary study. Now, in China more than 3000 cases of ERAT (using ERA as a diagnostic tool) have been preformed and it is recognized that it is not necessary to admit the patients to hospital. The procedure can also be performed in outpatient settings which is currently widely practiced in China.
This is a preliminary study with a limited sample size, a prospective controlled randomized trial is necessary to provide more valuable information for clinical implication of endoscopic retrograde appendicography. However, with the development of colonoscopic technology, we believe this method will become the most reliable method of diagnosis for acute appendicitis in the future.