Jessica Stewart MD, Presenter: Nothing to Disclose

Eric West Olcott MD, Abstract Co-Author: Nothing to Disclose

Jarrett Rosenberg PhD, Abstract Co-Author: Nothing to Disclose

R. Brooke Jeffrey MD, Abstract Co-Author: Nothing to Disclose

Non-visualization of the appendix on ultrasound (US) occurs frequently, and these patients are often directly referred for CT because this US result is considered noncontributory. The purpose of this study was to determine the incidence of perforated and non-perforated appendicitis in patients with non-visualization of the appendix on US. We also evaluated the diagnostic value of CT scans in this patient group.

A retrospective review of 400 consecutive appendiceal US studies for adult and pediatric patients was conducted. US images were interpreted by one radiologist blinded to the original imaging reports, with other information obtained by chart review. Of the 400 US studies reviewed, 140 (35%) demonstrated visualization of the appendix, 255 (63.8%) had non-visualization of the appendix without secondary signs of inflammation, and 5 (1.2%) had non-visualization of the appendix with secondary signs.

There were 75 cases of appendicitis in the 400 patient group (18.8%); 17 of these cases were perforated (4.25% of 400). Of the patients with non-visualization of the appendix on US without secondary signs, only 14 patients (5.5%) had appendicitis, and 2 were perforated (0.78% of 255). The prevalence of perforated and non-perforated appendicitis in this group was significantly lower than that of the 400 studies reviewed, with p-values < 0.0001 and < 0.0084, respectively. Of these 255 patients, 11 patients found to be positive for appendicitis and 90 patients negative for appendicitis had CT scans. Of the 90 patients without appendicitis, only 12 (13.3%) had another acute intra-abdominal process identified by CT.

Patients with non-visualization of the appendix and no secondary evidence of appendicitis on US have a very low risk of appendicitis (perforated and non-perforated). There is little diagnostic utility of CT scan in these patients, with 77.2% of CT scans not demonstrating appendicitis or another acute intra-abdominal pathology. We suggest that active clinical observation is appropriate for these patients, and that immediate referral for CT is not justified. This approach would spare patients unnecessary radiation and reduce cost.

Non-visualization of the appendix by US is a clinically useful finding that indicates a low risk of appendicitis, suggesting that these patients may be safely observed and avoid direct referral to CT.

Stewart, J, Olcott, E, Rosenberg, J, Jeffrey, R, Ultrasound for Appendicitis: Clinical and Imaging Implications of Nonvisualization of the Appendix.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11005488.html