Epiploic Appendagitis or Localised Omental Infarct?
[May 2018]

Segmental or focal omental infarction with or without mesenteritis is a rare, benign, and acute and sometimes chronic fibrosing inflammation disease of the mesenteric fatty tissue. The pathophysiological process may be similar to that of epiploic appendagitis [(1-5)], with the infarcted fatty tissue being part of the omentum. It can occur at any age but most com-monly in the fifth decades with a mean age at diagnosis of about 40 years similar to epiploic appendagitis [(6-8)].

Its etiology is unknown. Predisposing factors have been described including congenital abnor-malities of the omentum, focal inflammation with or without thrombosis, in association with neoplasia, after interventions including laparotomy with damage of blood vessels and after strenuous exercise [(6, 9)]. In addition obesity, trauma and other factors have been discussed. Partial omental infarction is a complication of omental transection while performing the an-tecolic approach to the laparoscopic Roux-en-Y gastric bypass. It can result from the following predisposing factors: structural anomalies in the omentum and its veins (particularly of the right side), thrombophilia, circulatory insufficiency and vascu-litis as well as obesity, cough, excessive physical exertion and an abrupt change of the position of the torso [(10)]. The secondary nature of this pathology is a consequence of abdominal surgery, trauma, inflammation, presence of a cyst and abdominal hernia. In these cases, lesions can be located at various sites in the abdominal cavity [(11, 12)].

To our experience it can occur at any location of the omentum but the right upper abdominal regions are more often involved compared to the left lower side, which is typical for diverticu-litis and epiploic appendagitis (which can occur left or right sided) [(13, 14)].

The symptoms and imaging features are similar to epiploic appendagitis [(15)] with acute or subacute upper (mid) abdominal pain and variably rebound tenderness and palpable mass (both up to 30 %) using physical examination [(16-18)]. Typically ultrasound supports physical examination with more frequently observed rebound tenderness and palpable masses. The right and left lower abdomen is a typical location for appendagitis. Less frequently observed symptoms include fever, vomiting, diarrhea or constipation. The white blood cell count, eryth-rocyte sedimentation rate, and C-reactive protein are mildly elevated or normal [(9, 19)]. The differential diagnosis of segmental or focal omental infarction include epiploic appendagitis, acute diverticulitis and acute appendicitis and many other inflammatory gastrointestinal dis-eases [(20-26)].

Transabdominal ultrasound typically shows a focal solid and non-compressible, solid, hy-perechoic ovoid lesion sometimes with a peripherally located hypoechoic (inflammatory) rim [(1-3, 9)]. A typical ultrasound image of omental infarction is characterized by: a slightly or moderately hyperechoic plaque-like mass greater than 35 - 50 mm located under the ab-dominal integuments to the right of the navel. Appendagitis tends to be smaller. The mass is sensitive to compression but with no visible compressibility [(10)]. Sometimes, the lesion is surrounded with a hypoechoic rim, or slight amounts of fluid are found in the vicinity. Colour Doppler Imaging (CDI) typically reveals absence of blood flow in the mass lesion similar to appendagitis and other ischemic diseases [(15, 27-30)] but contrast enhanced ultrasound is much more sensitive [(26, 31-39)]. However, vessels on the periphery of a central hypoechoic necrotic area have been observed in children with this pathology [(10)]. The pathological mass gives a similar US image to that of necrotic fat tissue at other abdominal sites. Most often isoechoic to the surrounding tissue the appearance varies from slightly hyperechoic to more often centrally located hypoechogenicity [(15, 40, 41)]. The echogenicity depends on the in-flammatory process and inflammatory vessels or infarct. It is typically iso- or hyperechoic, non-vascularized, sensitive and shows no compressibility [(11)]. Strain elastography and shear wave elastography [(42-51)] may reveal stiffer tissue than the surrounding. Ultrasound typi-cally shows an oval shaped and non-compressible painful mass directly under the abdominal wall. Magnetic resonance imaging (MRI) findings may be similar to the described CT findings [(52)].

Omental infarction should be part of the differential diagnosis, including anastomotic leak, in patients who develop abdominal pain 3-4 days after laparoscopic Roux-en-Y gastric bypass [(53)]. In approximately 90% of cases, the site of primary infarction (torsion) of the greater omentum is the right side. It can be mistaken for an exophytic tumor of the pancreas [(54)]. Omental infarction should be considered as a differential diagnosis for acute right-sided ab-dominal pain, especially in obese children [(55)]. In the absence of inflammation imaging is more difficult. In contrast epiploic appendagitis is a 20 to 30 mm, oval-shaped, fat density, paracolic mass with thickened peritoneal lining and peri-appendageal stranding [(9, 28, 56-61)]. Appendagitis often shows an inflammatory perilesional inflammatory reaction, which is less pronounced in omental infarction. The course of the disease is more prolonged in omental infarction compared to appendagitis as shown in our case. However, since both enti-ties present with the same symptoms, clinical and imaging findings and both are treated by symptomatic anti-inflammatory devices the differential diagnosis has no practical conse-quence [(9, 62-65)]. This is mainly true due to the benign course of the diseases.
Infarction of the lesser omentum is rare and a diagnostic challenge. The clinical picture of this pathology, including its spontaneous resolution, resembles infarction of the greater omentum. The only difference is the site, i.e. the position of a lesion between the left liver lobe, pancreas and stomach.

Because infarction of the greater omentum clinically resembles appendagitis and appendici-tis, its assessment is very important from the point of view of adequate patient management since the thickened omentum can at times conceal an underlying pathology. In the considera-ble majority of cases, omental infarction resolves spontaneously without specific treatment [(10)]. Inaccurate diagnosis can lead to unnecessary hospitalizations, antibiotic therapy, and surgical intervention [(56, 57, 66-69)]. If the disease is diagnosed in an ambulatory setting they usually do not require hospitalization, antibiotics [(70)] or surgery [(71)]. Surgery should be omitted whenever possible but intestinal obstruction and intussusception have been de-scribe in similar diseases [(71)].

In conclusion, local omental infarct with or without inflammatory changes is a benign and self-limiting condition. Complete resolution without surgical intervention usually occurs within weeks. The time to recover is generally longer than in an appendagitis [(9, 29, 62, 63)]. The lesion undergoes involution, mainly with fibrosis, sometimes with calcifications or adhesions between adjacent tissues. At times, a necrotic fragment detaches to the peritoneal cavity and behaves as a loose body [(10, 72)]. The risk of recurrence is probably low. Complications in-cluding abscess formation have been described, especially after surgery [(72)].

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Figure 1: B-mode ultrasound using low frequency (a) and high frequency (b) revealed an isoechoic mass with a hypoechoic circumference. The mass was not adher-ent to the colon. Contrast enhanced ultrasound using low frequency (c) and high frequency (d) revealed that it was a non-enhancing segment of the omentum. Strain elastography showed that the lesion was stiffer than its sur-rounding tissue.

Figure 2: Computed tomography confirmed the finding of a partially infarcted omentum.

Figure 3: A follow up examination few weeks later revealed partially revascularised omental tissue in a now asymptomatic patient (a,b). Shear wave elastography is shown where there is now only relatively soft (inflammatory) tissue (c).