Epiploic appendagitis is a rare self-limiting ischemic/inflammatory process involving appendix epiploica of the colon and may either be primary or secondary to adjacent pathology. This article pertains to primary (spontaneous) epiploic appendagitis. The term along with omental infarction is grouped under the broader umbrella term intraperitoneal focal fat infarction 9.
This condition usually affects patients in their 2nd to 5th decades with a predilection for women and obese individuals, presumably due to larger appendages 6.
Clinically, patients present with abdominal pain and guarding. It is essentially indistinguishable from diverticulitis and acute appendicitis (depending on location) and, although an uncommon condition, it accounts for up to 7% of cases of suspected diverticulitis 1. Since there is focal peritoneal irritation, pain may be more localized than with other causes of acute abdominal pain.
Epiploic appendagitis merely denotes inflammation of the one or more appendices epiploicae, which number 50-100 and are distributed along with the large bowel with variable frequency 3,4,6:
- rectosigmoid junction: 57%
- ileocecal region: 26%
- ascending colon: 9%
- transverse colon: 6%
- descending colon: 2%
The pathogenesis is thought to be due to torsion of a large and pedunculated appendage epiploicae, or spontaneous thrombosis of the venous outflow, resulting in ischemia and necrosis 3.
Ultrasound evaluation of the patient's area of maximal tenderness may reveal a rounded, non-compressible, hyperechoic mass, without internal vascularity, and surrounded by a subtle hypoechoic line 5. They are typically 2-4 cm in maximal diameter.
They typically exert local mass effect but are not usually associated with bowel wall thickening or ascites 5.
The CT appearance is usually characteristic:
- a fat-density ovoid structure adjacent to the colon, usually 1.5-3.5 cm in diameter 2
- thin high-density rim, known as the hyperattenuating ring sign (1-3 mm thick) 5,6
- surrounding inflammatory fat stranding, and thickening of the adjacent peritoneum
- a central hyperdense dot (representing the thrombosed vascular pedicle) 6
- adjacent colonic wall thickening is not usually associated, but if present is usually minimal and the amount of fat inflammation is out of proportional to colonic wall thickening
- the inflamed appendage is classically located on the anterior aspect of the sigmoid or descending colon, but it may be located anywhere along the circumference of the colon, as seen in the atypical Case 22.
Chronically, an infarcted epiploic appendage may calcify and may detach to form an intraperitoneal loose body (peritoneal 'mice').
It may rarely involve the vermiform appendix epiploic appendages as so-called "epiploic appendagitis of the vermiform appendix" 8, mimicking appendicitis both clinically and potentially on CT.
Although uncommonly used in a setting of acute abdominal pain, MRI features are also characteristic 6:
- T1: often shows a rounded high signal mass with slightly reduced signal compared to normal fat, due to inflammatory stranding; hypointense 2-3 mm rim
- T2: often seen as a high signal mass which attenuates on fat-suppressed sequences; hyperintense 2-3 mm rim with surrounding high signal stranding; central low signal vein
- T1 C+ (Gd): shows vivid rim enhancement
Treatment and prognosis
Epiploic appendagitis is a self-limiting disease, and thus correct identification on CT prevents unnecessary surgery 2. Although it sometimes mimics acute abdominal diseases for which surgery is required, treatment options for epiploic appendagitis often do not include surgery; it usually responds well to NSAIDs.
Imaging differential considerations include:
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