Omental Infarct

Published on 19/07/2015 by admin

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Last modified 19/07/2015

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 Heterogeneous, encapsulated mass located within omentum (usually in right lower quadrant)

– Surrounding inflammatory change and fat stranding ± small free fluid
image Variable attenuation, but usually foci of fat attenuation
image Usually well circumscribed with peripheral hyperdense rim 

– May appear ill defined as poorly marginated fat stranding without discrete mass in earliest stages
image No central dot sign (seen with epiploic appendagitis)
image Whorled pattern of vessels leading to infarct may reflect torsion of vessels feeding omentum
• Ultrasound appearance

image Hyperechoic, nonmobile, noncompressible fixed mass arising in omentum

– Decreased or absent flow within echogenic mass
image Focal tenderness with graded compression

PATHOLOGY

• Most cases idiopathic (obesity is predisposing factor)
• Other causes include abdominal surgery, trauma, incarcerated hernia, etc.

CLINICAL ISSUES

• Clinical presentation may mimic acute appendicitis

image Usually normal WBC and lack of nausea, vomiting, diarrhea, or constitutional symptoms
• Benign disorder almost never associated with complications
• Usually self-limiting process that resolves spontaneously and should be treated only with pain management
• If diagnosed prospectively on CT, surgery should not be performed
image
(Left) Axial CECT in a patient with abdominal pain demonstrates an ill-defined, fat-containing mass image in the omentum with a subtle peripheral rim, in keeping with an omental infarct. The patient’s pain resolved in a few days with conservative therapy.

image
(Right) Axial CECT demonstrates a well-circumscribed fatty mass image with a peripheral hyperdense rim in the right omentum. The patient had experienced RLQ pain about 1 week earlier, and this was thought to be a subacute omental infarct.
image
(Left) Axial CECT in a patient with abdominal pain shows a classic omental infarct as a fatty mass image with a hyperdense rim adjacent to the ascending colon.

image
(Right) Axial CECT in the same patient demonstrates a “swirled” appearance of an omental vessel image within the infarcted omentum, indicating twisting of the omental pedicle, which may be the etiology of the infarct in some cases.

TERMINOLOGY

Definitions

• Fat necrosis caused by interruption of arterial blood supply to omentum

IMAGING

General Features

• Best diagnostic clue

image Focal mass of heterogeneous density within omental fat with surrounding soft tissue inflammation
• Size

image Varies from 3.5-15 cm
image Larger infarcts often associated with surgery
• Morphology

image Focal heterogeneous mass composed of inflamed omental fat ± hemorrhage
image Usually well circumscribed, and appear triangular, ovoid, or cake-like in shape

CT Findings

• Heterogeneous, encapsulated mass located within omentum between anterior abdominal wall and colon

image Can have variable internal attenuation, but usually some internal foci of fat attenuation (-20 to -50 HU)
image Usually well-circumscribed margins with peripheral hyperdense rim, particularly when occurring after surgery

– Infarcts in earliest stages may appear ill defined: Sites of poorly marginated fat stranding without discrete mass
image Does not have central dot sign seen with epiploic appendagitis
image Whorled pattern of vessels leading to infarct may reflect torsion of vessels feeding omentum
• Often associated with surrounding inflammatory change and fat stranding ± small free fluid
• May be adherent to either colon or parietal peritoneum

image Only rarely causes reactive colonic wall thickening
image Rarely causes reactive thickening of overlying abdominal wall
• Usually located in right inferior omentum, especially when idiopathic

image Usually located adjacent to site of surgery when occurring in postoperative setting

Ultrasonographic Findings

• Grayscale ultrasound

image Echogenic, nonmobile, noncompressible fixed mass arising in omentum

– Associated with focal tenderness when graded compression applied to site
– Echogenic fat surrounding mass (reflects inflammation) ± small free fluid
• Color Doppler

image Decreased or absent flow within echogenic mass

Nuclear Medicine Findings

• PET/CT

image Omental infarcts may demonstrate FDG avidity suggesting tumor (if not correlated with CT appearance)

Imaging Recommendations

• Best imaging tool

image CECT
• Protocol advice

image 

DIFFERENTIAL DIAGNOSIS

Acute Appendicitis

• Can mimic omental infarction clinically, but distinction readily made with cross-sectional imaging
• Dilated appendix with wall thickening, mucosal hyperemia, and periappendiceal fat stranding, inflammation, and free fluid

image May demonstrate reactive wall thickening of cecum or terminal ileum
image Fluid collection, abscess, or ectopic gas in setting of perforation
image Appendicolith may be seen in 10-15% of cases
• Noncompressible appendix ≥ 7 mm on graded compression US often with increased color flow vascularity

Epiploic Appendagitis

• Benign and self-limited disorder: 1% of patients with acute right lower quadrant pain

image Most commonly caused by primary thrombosis or torsion of epiploic appendage, but rarely secondary to adjacent inflammation (diverticulitis, appendicitis, etc.)
• May appear similar to omental infarct, but distinction is irrelevant, as both entities treated conservatively
• CT: Small fatty mass with hyperattenuating ring abutting colon with mild adjacent fat stranding

image Central dot sign due to thrombosed vessel commonly present, not seen with omental infarcts
image May rarely cause reactive wall thickening of colon and thickening of parietal peritoneum
image Most common in left lower quadrant (rectosigmoid), unlike omental infarcts which occur in right lower quadrant

Liposarcoma

• Large omental infarcts can mimic fatty tumor (i.e., liposarcoma)
• Distinction based on clinical presentation (omental infarcts present with acute pain) and change over time (tumor grows over time while infarct should get smaller)
• Biopsy may be required in some rare cases

Pancreatitis With Extrapancreatic Fat Necrosis

• Focal or diffuse enlargement of pancreas with peripancreatic fluid and stranding ± fluid collections
• 

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