Epiploic appendages are peritoneal outpouchings attached to the serosal surface of the colon that contain fat and blood vessels. They occur anywhere from the cecum to the sigmoid, are largest in the sigmoid, and are generally only visible when they are inflamed (i.e. if surrounded by ascites). Torsion of an epiploic appendage or thrombosis of its central vein causes epiploic appendagitis.
Patients typically present with acute abdominal pain, usually in the left lower quadrant which often leads to its being mistaken for acute diverticulitis (it may be mistaken for acute appendicitis if a cecal epiploic appendage is involved).
CECT will demonstrate an ovoid, fat containing mass adjacent to the anterior colonic wall. Surrounding inflammatory changes are typically seen. A hyperattenuating ring around the mass may be seen. The central dot sign - presence of central high attenuation representing the thrombosed vein - is seen in a minority of cases. Reactive thickening of the adjacent colon may be seen.
The above images are from a patient who presented to the emergency room and was worked up for acute diverticulitis. No colonic diverticula were seen. Instead, in the left lower quadrant there is an ovoid, fat containing mass with inflammatory changes and the central dot sign (arrow). The findings are compatible with epiploic appendagitis.
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Singh AK, Gervais DA, Hahn PF, et al. Acute epiploic eppendagitis. Radiographics 2005;25:1521-34.