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Background
The epiploic appendage is a ubiquitous entity in the abdomen. It may become visible on MDCT scans in certain conditions, or manifest as focal inflammation. It may also be seen remote from its origin. Recognition of its many faces is important to avoid misdiagnosis.

Educational Goals / Teaching Points
Recognize the myriad appearances of epiploic appendage on MDCT. Accurately diagnose epiploic appendagitis and distinguish it from other conditions it mimics.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Epiploic appendages are peritoneum-lined protrusions of fat that arise from the colonic surface. They originate in two rows (anterior and posterolateral) parallel to the external surface of taenia coli. There is only one row along transverse colon and none along rectum. Epiploic appendages are 0.5 - 5 cm long, each supplied by 1-2 small colonic end-arteries and a small draining vein, which pierce colonic wall between taeniae, creating points of weakness where diverticula may arise. Being of fat attenuation with thin walls, these are visible on CT only when inflamed or surrounded by fluid/ inflammation. Torsion of epiploic appendages with vascular (venous) occlusion leading to ischemia has been implicated as the cause of acute epiploic appendagitis. CT findings include an oval lesion of fat attenuation less than 5 cm in diameter that abuts the anterior or lateral colonic wall and is surrounded by inflammation. Colonic wall is most often of normal thickness. Intestinal obstruction and abscess formation are rare. Although presence of a central area of high attenuation (venous thrombosis) is useful for diagnosis, absence of this feature does not preclude it. Differential diagnosis of inflammatory fatty lesion in a patient with acute abdomen includes acute epiploic appendagitis, omental infarction and inflammatory processes such as diverticulitis. Epiploic appendagitis located near the appendix mimics acute appendicitis. A pseudolipoma may result from detached epiploic appendage that develops a fibrous capsule. When this lesion is in proximity to liver, called pseudolipoma of Glisson capsule, it may become attached to the hepatic capsule. Differential diagnosis includes serosal metastasis and fibrosing subcapsular necrotic nodule of liver. At imaging, it appears as a circumscribed nodule of fat attenuation on peritonealised liver surface. Chronically infarcted epiploic appendages may detach and calcify, appearing as intraperitoneal loose bodies. Many are incidentally found during abdominal surgery or CT performed for unrelated conditions. Most are small in size (diameter 1–3 cm), with an oval shape and patchy “popcorn” or peripheral “eggshell” calcification. They can be potentially mistaken at imaging for dropped gallstones, calcified lymph nodes or uterine fibroids. Very rarely, an epiploic appendage can protrude into hernia sac and become irreducible, requiring emergent surgical intervention.

Conclusion
Though epiploic appendages are ubiquitous in the abdomen, they are sometimes forgotten as a potential cause for acute or incidental findings on abdominal CT. Knowledge of the many faces of an epiploic appendage precludes misdiagnosis.