Diagnostic Ultrasound - Abdomen and Pelvis

Segmental Omental Infarction
TERMINOLOGY
Abbreviations
• Omental infarction (OI)
Definitions
• Primary (idiopathic) OI refers to vascular compromise of
omentum, ± torsion
• Secondary OI may result from torsion due to: (a)
attachment to acquired lesion (e.g., surgical scar and
neoplasm), (b) trauma, or (c) hernial incarceration
IMAGING
General Features
• Best diagnostic clue
○ Ovoid/cake-like predominantly fat attenuation/density
omental mass
• Location
○ Located between abdominal wall and colon, usually on
right side
– 82% lower and 15% upper quadrant
• Size
○ Usually > 5 cm (3.5-10 cm)
Imaging Recommendations
• Best imaging tool
○ CECT is often diagnostic, non-operator dependent, and
allows better depiction/interrogation
○ Focused high-resolution ultrasound at point of maximal
tenderness with typical ultrasound appearances can be
diagnostic
○ Often clinically unsuspected and ultrasound may be
initially performed to exclude alternative diagnosis (e.g.,
appendicitis or cholecystitis)
CT Findings
• CECT
○ Abnormal omental fat located between rectus
abdominis and colon
– Appearances may be of focal fat haziness or, more
commonly, a large (> 5 cm) nonenhancing
heterogeneous omental mass with fat stranding
○ Central dot sign may be present (central
hyperattenuating focus representing central engorged
or thrombosed vessel/hemorrhage)
○ Normal appearances to adjacent colon, gallbladder, and
appendix
○ Less commonly there may be free fluid and minimal
colonic reactive thickening
Ultrasonographic Findings
• Grayscale ultrasound
○ Noncompressible focal echogenic fat with mass-like
appearances, located directly beneath abdominal wall, at
site of maximal tenderness
○ Color flow mapping shows mass to be avascular
– Peripheral hyperemia may be present
○ Poorly defined nodular or linear hypoechoic avascular
areas within hyperechoic mass
DIFFERENTIAL DIAGNOSIS
Acute Appendicitis
• Dilated noncompressible appendix (> 6 mm) ±
appendicolith
• Ancillary findings: Periappendiceal fat stranding, reactive
cecal/terminal ileal thickening, free fluid, ± appendicular
abscess
Acute Cholecystitis
• Thick-walled gallbladder with pericholecystic edema/free
fluid
Right-Sided Diverticulitis
• Presence of right-sided diverticula with associated colonic
thickening
Epiploic Appendagitis
• Focal lesion (< 5 cm) located adjacent to sigmoid colon in
majority of cases
• Presence of hyperattenuating ring sign representing
inflamed visceral peritoneum, absent in OI
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Constant nonradiating right flank/lower abdominal pain
gradually increasing in intensity over a few days
○ Local peritonism ± palpable mass
○ Radiological features lag clinical improvement
• Other signs/symptoms
○ Commonly afebrile, mild leukocytosis
Demographics
• Age
○ Adult predominance; 15% of cases occur in pediatric
population
• Gender
○ Male predominance (2:1)
• Precipitating factors
○ Primary OI
– Obesity (irregular accumulations of omental fat),
anatomical omental variations (including accessory
and bifid omentum and narrowed omentum pedicle)
○ Secondary OI
– Hernia, neoplasm, adhesions, trauma, or postsurgical
Treatment
• Conservative management with nonsteroidal therapy
SELECTED REFERENCES
1. Yoo E et al: Greater and lesser omenta: normal anatomy and pathologic
processes. Radiographics. 27(3):707-20, 2007
2. Baldisserotto M et al: Omental infarction in children: color Doppler
sonography correlated with surgery and pathology findings. AJR Am J
Roentgenol. 184(1):156-62, 2005
3. Singh AK et al. Acute Epiploic Appendagitis and Its Mimics. Radiographics.
25(6): 1521-34, 2005
4. Grattan-Smith JD et al: Omental infarction in pediatric patients: sonographic
and CT findings. AJR Am J Roentgenol. 178(6):1537-9, 2002
Diagnoses: Abdominal Wall/Peritoneal Cavity
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