Hyperdense appendix on unenhanced CT: a sign of acute appendicitis

The purpose of this study was to evaluate the presence of the hyperdense appendix in acute appendicitis. The CT scans of 183 patients with pathologically proven acute appendicitis were reviewed to determine the prevalence of a hyperdense appendix, defined as a high-attenuated appendix when compared with the adjacent cecal wall on precontrast CT. A control group consisted of 100 patients with CT examinations performed in the emergency department were also randomly allocated to search for any hyperdense appendix in other disease conditions. The images were reviewed by two radiologists who reached a decision by consensus. A hyperdense appendix sign was found in 61 of 183 (33%) patients, including 92 men and 91 women ranging in age from 17 to 85 years (mean 37 years). On the other hand, the sign was seen in only two (2%) of the 88 patients in whom appendicitis was not diagnosed. The hyperdense appendix sign on unenhanced CT is seen in about 33% of patients with acute appendicitis. The false-positive rate is very low, rendering it a very useful sign for diagnosis of acute appendicitis.