3.5\ Epiploic Appendagitis

Epiploic appendages are pedunculated fat-filled structures protruding from the external surface of the colon into the peritoneal cavity. They vary considerably in size, shape, and contour, but they are usually 1–2 cm thick and 0.5–5 cm long and they are larger on the left side of the colon. They are presumed to serve a protective cushion during peristalsis. Epiploic appendages have limited blood supply and are highly mobile which makes them prone to torsion, ischemia, and hemorrhagic infarction. When this happens it is known as epiploic appendagitis, hemorrhagic epiploitis, or epiploic appendicitis. It is a rare, benign, and self-limiting pathology. It occurs most commonly in the second to fifth decades of life, with a similar incidence among men and women (Almeida et al. 2009). The most common presentation is with sudden onset of abdominal pain without leukocytosis and fever (Rao and Novelline 1999).

3.5.1\ Imaging Findings

Normal epiploic appendages are not usually seen on CT or MR unless there is a sufficient amount of surrounding intraperitoneal fluid, either ascites or hemoperitoneum (Fig. 20). Imaging findings of epiploic appendagitis include an oval-shaped

Fig. 20  Normal epiploic appendices on CT. Epiploic appendices of the sigmoid colon present pedunculated fat structures, which protrude from the sigmoid surface into the peritoneal cavity (arrow). They are easily visualized because of ascites in this woman with peritoneal carcinomatosis. Small sigmoid diverticula which present air-con- taining mural outpouchings into the peri-sigmoid fat tissue are also demonstrated (arrowhead)

Fig. 21  Epiploic appendagitis. Axial CT shows soft-tis- sue infiltration (arrow) with adjacent reticular fatty infiltration in the left iliac fossa. The well-circumscribed hyper-attenuating rim is more consistent with epiploic appendagitis than omental infarction

fingerlike paracolic mass with fat attenuation and peri appendiceal fat stranding (Pereira et al. 2005). On CT, the density tends to be higher than uninvolved fat. A well-circumscribed hyperattenuating rim surrounding the mass representing the inflamed visceral peritoneal lining is a characteristic finding (Fig. 21). Adjacent colonic wall thickening and compression may also be seen (Rao and Novelline 1999). Sometimes a high attenuation central dot representing thrombosed central vessels or central areas of hemorrhage can be seen (Pereira et al. 2005). Rarely, dystrophic calcification from a previously infarcted appendage may be evident (Pickhardt and Bhalla 2005). On MRI, the inflamed epiploic appendage is slightly less hyperintense than the adjacent peritoneal fat and shows marked signal loss on fat suppression sequences. The inflammatory rim is hypointense on T1-weighted images and hyperintense on T2-weighted images. The central draining vein is hypointense on both T1and T2-weighted images (Almeida et al. 2009).

3.5.2\ Differential Diagnosis

Segmental omental infarction, which is often localized on the right side of the omentum, has a similar appearance to epiploic appendagitis. Imaging findings range from subtle focal hazy soft-tissue infiltration of the omentum to a