Presence or absence of gas in the appendix: Additional criteria to rule out or confirm acute appendicitis - Evaluation with US

PURPOSE: To investigate whether the presence or absence of gas in the appendix may be considered as additional ultrasonographic (US) criteria to rule out or confirm acute appendicitis. MATERIALS AND METHODS: The appendices in 239 control subjects, 138 patients with lower right quadrant pain without acute appendicitis, and 80 patients with acute appendicitis were prospectively evaluated for intraluminal gas with US. RESULTS: The appendices in 206 (86%) control subjects showed gas at US, and those in 33 (14%) did not. The appendices in 109 (79%) symptomatic patients without acute appendicitis showed gas, and those in 29 (21%) did not, The appendices in 12 (15%) patients with acutely inflamed appendices showed gas, and those in 68 (85%) did not. The absence of gas as a criterion for acute appendicitis had a sensitivity of 85%; specificity, 79%; positive and negative predictive values, 57% and 94%, respectively; and accuracy, 81%. Gas was useful to exclude acute appendicitis in 64 (46%) symptomatic patients because the established criteria were misleading. In 19 (24%) patients, the absence of gas was useful for diagnosis of acute appendicitis because the other criteria were not convincing. CONCLUSION: US-based detection of gas in the appendiceal lumen helps to rule,out acute appendicitis, whereas the absence of gas further confirms its presence, especially in cases where established US criteria are either insufficiently present or misleading.