Keywords
omental infarction - acute appendicitis - computed tomography - whirl sign
Introduction
Omental infarction is a rare cause of acute abdominal pain and clinical diagnosis
is challenging due to its relatively low incidence and nonspecific presentation. Omental
infarct typically presents with right lower abdominal pain, vomiting, low-grade fever,
and occasionally with a palpable abdominal mass. Although clinically it is indistinguishable
from acute appendicitis and cholecystitis,[1] imaging findings and radiological diagnosis are more promising due to advancements
in technology in the recent past. Omental infarct occurs due to vascular compromise
of the greater omentum and is classified as primary or secondary. Secondary omental
infarction is caused due to adhesion between the omentum and pathological foci (hernia,
surgical scar, and tumors), hypercoagulable state, and mesenteric vein thrombosis
due to right heart failure.[2] If no cause is identified, then it is called idiopathic or primary omental infarction
that is likely due to anatomical variations like bifid, bulky or redundant omentum.
The diagnosis of omental infarction is primarily based on computed tomography (CT)
that allows conservative management. About 400 cases of omental infarction were reported
in literature; however, there is a paucity of larger case series describing the imaging
appearance.[3]
Aims and Objectives
The main purpose of this article is to describe the multidetector computed tomography
(MDCT) features of omental infarction in clinching the diagnosis and differentiating
from other causes of acute pain abdomen.
Methods
This is a retrospective review conducted from 2014 to 2019, of five patients with
MDCT diagnosis of omental infarction who had been referred to the department of radiology
with right lower and/or upper quadrant abdominal pain and with various clinical diagnoses.
Basic demographic data of the patients and clinical diagnoses were noted. Ultrasound
scans were unremarkable.
MDCT Technique
All patients underwent CT evaluation on a 16 slice MDCT scanner (General Electric
Medical Systems, Milwaukee, Wisconsin, United States) utilizing our contrast-enhanced
routine abdomen and pelvis protocol. Axial 5 mm thick sections were taken from the
lung bases to the pubic symphysis after injecting intravenously with 80 to 100 mL
of nonionic iodinated contrast (Omnipaque–300 mgI/mL) at a rate of 2 to 3 mL/s. Oral
or rectal contrast was not administered in all five cases as CT scan was done on an
emergency basis.
All five patients had noncontrast CT and at least one contrast-enhanced CT in the
portal venous phase (60s). The images were reconstructed utilizing multiplanar reformatted
images in sagittal and coronal planes using 1.5 mm section thickness and viewed in
multiple planes.
CT Findings
Imaging features such as size of the lesion, location, absence of rim enhancement,
relation to colon, and bowel wall thickening were included. CT findings were later
correlated with postoperative findings in two cases.
Results
Demographic Data with Clinical Presentation
Among the five patients, three were females and two were males with an age range of
36 to 55 years ([Table 1]). Pain was unrelated to meal intake. On physical examination, there was tenderness
on light palpation localized to right upper/lower abdominal quadrant with guarding.
No rebound tenderness was found and Murphy sign was negative. Other systemic examination
was unremarkable. Complete blood count, hepatic function tests, lipase, urinalysis,
and lactate levels were within normal limits. The electrocardiogram showed normal
sinus rhythm. Three cases were clinically diagnosed as acute appendicitis and two
cases were diagnosed as acute cholecystitis ([Table 2]).
Table 1
Demographic data of patients
|
Gender presentation
|
|
Males
|
2
|
|
Females
|
3
|
Table 2
Clinical presentation with clinical diagnosis
|
Clinical presentation
|
Clinical diagnosis
|
Cases
|
|
Right lower abdominal pain
|
Acute appendicitis
|
3
|
|
Right upper abdominal pain
|
Acute cholecystitis
|
2
|
MDCT Features
MDCT findings consisted of an ill-defined round-oval, heterogeneous fat-density lesion
with no definable continuous peripheral rim within the greater omentum in all cases
([Figs. 1]
[2]). Three cases were in the right iliac fossa and two cases were in the supraumbilical
region on the right side ([Figs. 2]
[3]). The lesions were related to cecum, ascending or transverse colon with no obvious
bowel wall thickening in all five patients ([Table 3]). Out of five cases, four cases were of primary infarct and one case was secondary
infarct ([Table 4]) that presented as right inguinal hernia with omental torsion ([Fig. 4]). Omental torsion on MDCT showed fat density lesion with whirling pattern of omental
vessels called the whirl sign ([Fig. 5]).
Table 3
MDCT features of omental infarct
|
Location of the omental infarct
|
|
Abbreviations: MDCT, multidetector computed tomography; RIF, right iliac fossa
|
|
RIF
|
3
|
|
Supraumbilical region
|
2
|
|
Location of omental infarct in relation to colon/bowel
|
|
Ascending colon
|
1
|
|
Transverse colon
|
2
|
|
Cecum
|
2
|
|
Size of lesion
|
|
>5cm
|
4
|
|
<2cm
|
1
|
|
Morphology of omental infarct on CT
|
|
In greater omentum
|
In all cases
|
|
Round to oval
|
|
Fat density lesion
|
|
No definable continuous peripheral rim
|
Table 4
Etiology for omental infarct
|
Secondary infarct (right inguinal hernia)
|
1
|
|
Primary omental infarct
|
4
|
Fig. 1 A 46-year-old man with acute right iliac fossa (RIF) pain. Axial and coronal contrast-enhanced
computed tomography images of the abdomen show an oval fat density lesion (arrowhead)
in the RIF with a broad base toward parietal peritoneum. The lesion is noted between
the ascending colon and the anterior abdominal wall.
Fig. 2 Axial and sagittal contrast-enhanced computed tomography images of the abdomen in
the subhepatic region show a fat density lesion (arrowhead) with hyperattenuating
streaky infiltration between the abdominal wall and transverse colon.
Fig. 3 Axial contrast-enhanced computed tomography abdomen of a 49-year-old female presenting
with acute right iliac fossa (RIF) pain shows an ill-defined heterogeneously enhancing
small fat density mass in RIF (arrowhead) abutting the parietal peritoneum.
Fig. 4 Secondary omental infarction: A 36-year-old lady presenting with acute right iliac
fossa (RIF) pain. Axial and sagittal contrast-enhanced computed tomography abdomen
images: Areas of fat density (curved arrow) seen in the RIF herniating into right
inguinal region with round ligament (arrowhead) and infarcted omentum as content.
Omental infarction was caused secondary to an inguinal hernia.
Fig. 5 Axial and coronal contrast-enhanced computed tomography abdomen images of Omental
torsion: Hazy omentum with concentric hyperdensity and whirling pattern in right iliac
fossa (arrowhead) and abutting the cecum posteriorly. It is called the “Whirl sign.”
Management
Three cases were managed conservatively and the other two cases were surgically managed
with histopathological diagnosis proven to be omental infarction in operated cases.
Discussion
Omental infarction was first described by Eithel in the year 1899.[4] The greater omentum is a large peritoneal fold and is continuous with visceral peritoneum
of stomach and transverse colon. It contains fat and blood vessels ([Fig. 6]). Omental infarct is rare due to extensive vascular collaterals to greater omentum
by epiploic arteries. However, as reported in the literature by Park et al, 88% of
infarction commonly occurs on the right side, likely due to the possibility of long
and mobile omentum.[3] Rarely the omental infarction can present on the left side or in the epigastric
region.[5] In our study, three cases presented in the right iliac fossa and the other two cases
in the supraumbilical region.
Fig. 6 The right and left gastroepiploic arteries provide blood supply to the greater omentum.
The right and left gastroepiploic arteries anastomose within the two layers of the
anterior greater omentum along the greater curvature of the stomach. Image courtesy:
ESGAR 2019[12]
In 85% of all cases of omental infarction reported in literature, it was found to
occur commonly in adults (40–50 years) presenting as acute or subacute right upper
or lower quadrant pain.[3] In our study, all cases presented with acute pain abdomen (1 day) on the right side.
Based on the clinical presentation, most of the cases were diagnosed as acute appendicitis
or acute cholecystitis[6] similar to our study.
Omental infarction was classified into two types as primary and secondary infarction
([Table 5]) by Leitener et al in 1952 and has been cited in many studies.[7] Secondary omental infarction is caused due to torsion of omental vessels caused
by adhesion between the omentum and pathological foci (hernia, surgical scar, and
tumors), hypercoagulable state and mesenteric vein thrombosis due to right heart failure.[2] If no cause was identified, then it is called idiopathic or primary omental infarction
that is likely due to anatomical variations such as bifid, bulky, or redundant omentum.
None of the patients in our study had any evidence of hypercoagulable state or previous
surgery. One of the patients in our study was diagnosed with omental torsion that
was secondary to right inguinal hernia. The rest of the patients (80%) had no identifiable
cause and were diagnosed as primary omental infarction.
Table 5
Causes of omental infarction
|
Primary omental infarction
|
Secondary omental infarction
|
|
Anatomical variants—bifid omentum
|
Adhesions (hernia, surgery)
|
|
Bulky or redundant omentum
|
Vasculitis and hypercoagulable state
|
|
Obesity
|
Omental cyst/tumor
|
|
Overeating
|
Internal or external hernia
|
|
Local trauma
|
Diverticulitis
|
|
Excessive exercise, cough
|
Congestive heart failure
|
|
Use of laxatives
|
|
The primary modality for the diagnosis of omental infarction is CT that shows a large
(> 5 cm) triangular or oval heterogeneous fat density lesion with no enhancing rim
or central hyperattenuating foci, which is centered in the greater omentum located
between anterior abdominal wall and colon.[5]
[8]
[9] In our study, the fatty lesion was > 5 cm in most of the cases (80%) and no evidence
of bowel wall thickening was found in all cases. However, rarely there may be bowel
wall thickening adjacent to an area of omental infarction due to reactive bowel wall
changes.[10]
Omental torsion in CT shows “whirl sign” that appears as streaks due to whirling of
omental vessels in concentric pattern.[11] The whirl sign is a sensitive indication of rotation of the mesentery and vessels
but is not specific to omental torsion alone and can be seen in small bowel obstruction,
intestinal malrotation, or volvulus.[12] In our study, whirl sign was seen in one case due to omental torsion secondary to
inguinal hernia ([Fig. 5]).
Imaging differential diagnosis on CT for omental fat stranding with acute pain abdomen
includes epiploic appendagitis. Epiploic appendagitis, presents as a fatty paracolonic
oval mass on the left side, is usually < 2 cm in size with central high attenuation
focus representing thrombosed vein and surrounded by hyperdense rim.[13] There was no evidence of high attenuation peripheral or central foci in any of our
five cases.
Usually, conservative treatment is recommended for omental infarction with analgesics
and anti-inflammatory drugs, as it is a self-limited disease. However, clinicians
should be alert for rare complications such as intestinal obstruction, adhesion or
abscess formation, which may need surgical exploration.[5] Two cases were surgically managed in our study, namely the one case with omental
torsion secondary to inguinal hernia and the other case with right iliac fossa fat
density lesion with severe intolerable abdominal pain.
Conclusion
Omental infarction should be considered in the differential diagnosis of acute pain
abdomen mimicking acute appendicitis, acute cholecystitis, diverticulitis, etc. MDCT
features such as oval heterogeneous fat density lesion in the greater omentum with
no high attenuation peripheral or central foci clinch the diagnosis of omental infarction
radiologically and avoid unnecessary surgery. Severe pain in the abdomen can be distressing
and typical imaging features of omental infarction allay anxiety and allow to treat
conservatively as it is a self-limiting disease. Hence, awareness of the imaging features
of acute omental infarction is important.
