Infected omental infarction: A rare complication

A 56-year-old female presented to the emergency department with abdominal pain localised to the right iliac fossa. The pain started 4 days earlier. The patient also reported constipation. There was no fever, vomiting, or nausea. The patient had undergone an appendectomy a few years prior.

On physical examination, there was tenderness in the right iliac fossa. The abdomen was soft with no palpable masses.

A slight increase in C-reactive protein was noted (5 mg/dL). Haemogram, liver function tests, amylase, lipase, and kidney function values were all normal.

On ultrasound, a hypoechogenic irregular lesion was seen in the transition between the right iliac fossa and the pelvis. Increased echogenicity of the surrounding fat was present (Figure 1), raising the hypothesis of an abscess.

A computed tomography (CT) scan confirmed an abscess medial to the cecum and anterior to the ileum, with marked fat stranding (Figures 2a and 2b). The nearby intestinal loops showed normal enhancement and thickness (Figure 2a). The appendectomy stump and the right ovary were unremarkable. Thus, an infected omental infarction was considered the most likely diagnosis.

A follow-up magnetic resonance imaging (MRI), one week after the CT, showed the lesion as hyperintense on T2 and hypointense on T1, confirming liquefied content (Figures 3a and 3b). There was also restriction on DWI, further confirming the abscess (Figures  3d and 3e). The lesion decreased in size between observations.

Omental infarct or omental torsion is a rare but potentially serious condition characterised by necrosis of a portion of the omentum [1]. This condition typically occurs due to a twisting or torsion of the omentum, leading to compromised blood flow and subsequent tissue death. When infection accompanies this infarction, it can escalate the severity of the condition, posing significant challenges in diagnosis and management [2].

The clinical presentation of infected omental infarction can vary widely, ranging from mild abdominal discomfort to acute abdomen with signs of peritonitis [1].

Due to its rarity and varied clinical presentation, infected omental infarction presents unique diagnostic challenges. Therefore, imaging plays a crucial role in identifying characteristic features that can aid in prompt diagnosis and guide appropriate management.

CT is the imaging modality of choice for suspected cases. A hallmark finding is the identification of a whirl-like pattern of the omental fat. This appearance, often referred to as the “whirl sign”, indicates torsion of the omentum, leading to compromised blood flow and subsequent infarction [3].

In addition to the whirl sign, CT may also reveal fat stranding and thickening of the affected omentum [1]. Furthermore, CT imaging may detect the presence of fluid collections or abscesses within the affected region, suggestive of associated infection [2], as seen in the present case.

Unlike inflammatory colitis, ileitis, or diverticulitis, omental infarction does not show bowel wall thickening or mucosal hyperenhancement. Inflammatory colitis often presents with diffuse or focal peri-colonic fat stranding, and diverticulitis commonly reveals diverticula as the origin of the inflammatory process. Ovarian torsion can also be a differential diagnosis, but it typically presents with an enlarged ovary, absence of Doppler flow, and free pelvic fluid [3].

In this particular case, stump appendicitis was considered, but the residual appendix was not thickened, and the fat stranding did not involve the stump.

If CT findings are inconclusive, further imaging modalities such as MRI or ultrasound may be considered. MRI can provide additional soft tissue contrast and may be helpful in cases where CT findings are equivocal or when evaluating for complications such as abscess formation [2]. Ultrasound may also be used as a complementary imaging modality, particularly in paediatric or pregnant patients, although its sensitivity and specificity for diagnosing omental infarction may be limited compared to CT [2].

Treatment is usually conservative with analgesia, involving anti-inflammatory medications, and observation, as the condition often resolves spontaneously. In cases such as this one, where an abscess is present, antibiotic therapy is also needed [2].

In summary, CT imaging plays a crucial role in the diagnosis of infected omental infarction by identifying characteristic features such as the whirl sign, inflammation, and associated complications. Radiologists should be familiar with these imaging findings to facilitate prompt recognition and appropriate management of this uncommon but clinically significant condition.

Written informed patient consent for publication has been obtained.