Sonographic and CT imaging findings of epiploic appendagitis and its mimics

A 28-year-old male patient presented at the emergency room with a history of left lower quadrant pain for the past 3 days. Clinically it was suspected to be a diverticulitis and he was referred for abdominal ultrasound and followed by contrast-enhanced CT abdomen with oral contrast administration. Routine blood examination findings were normal, except for mild leucocytosis.

Ultrasound of the abdomen showed normal sonographic appearance of the abdominal viscera. An ovoid non-compressible echogenic mass with hypoechoic rim was seen in the omentum, adjacent to the anterior peritoneal wall (in the left lower quadrant of the abdomen), at the point of tenderness, however, no vascularity was seen on colour Doppler evaluation.
Contrast-enhanced CT scan showed an ovoid well-defined fat attenuation lesion with hyperdense rim adjacent to the distal descending colon in the left iliac fossa, with associated fat stranding and mild colon thickening, s/o epiploic appendagitis.
Our patient was managed conservatively and improved on follow up scan.

Acute epiploic appendagitis is an acute abdominal condition. Pathophysiology of this condition includes torsion of an epiploic appendage, with resultant vascular occulsion, which leads to ischaemia and is seen as epiploic appendagitis [1]. It is a self-limiting condition in the majority of the patients, rarely it can cause adhesions, intussception, bowel obstruction, peritonitis and abscess [1].

Diagnostic sonographic findings are non-compressible oval hyperechoic mass with hypoechoic rim (due to inflamed visceral peritoneum), absence of colour flow on Doppler and point of maximum tenderness and it may contain central hypoechoic areas of haemorrhage [2].
Most common CT findings of epiploic appendagitis include ovoid fat density mass, diameter less than 5 cm, with hyperdense rim, usually seen adjacent to the colonic wall with surrounding inflammatory change [1, 3]. Thickening of the adjacent parietal peritoneum may also occur, secondary to adjacent inflammation. The adjacent colon wall may be thickened or may appear normal. Another CT sign is the central dot sign, which is due to the presence of a central thrombosed vein to the epiploic appendage and specific for the diagnosis of epiploic appendagitis, however, it is not present in all cases [3].

The differential diagnosis includes omental infarction, which may mimic epiploic appendagitis. However, CT scan differentiates between these two entities. Typical CT findings of omental infarct are an omental mass without obvious hyperdense rim and located commonly in the right side of the abdomen, anterior to the transverse colon or anteromedial to the transverse colon.
Another mimic is acute diverticulitis, which was the clinical suspicion in our case. It commonly affects the sigmoid colon and CT findings are characteristic, which include multiple colonic diverticula with inflammatory changes involving the diverticulum, associated colon wall thickening and fat stranding in the adjacent mesocolon. Complicated diverticulitis can also be differentiated from other conditions, where CT features of pericolonic abscess, perforation, fistula or abscess formation may also occur.

Teaching points:
Acute epiploic appendagitis usually presents with acute abdomen and clinically can mimic other serious inflammatory conditions, like diverticulitis or urinary obstruction. Knowledge of its USG and CT findings would help the radiologist to make the accurate diagnosis and appropriate conservative management and patient care accordingly, as it is a self-limiting entity.

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