Fat stranding refers to an abnormal increased
attenuation in fat.
Abdominal fat stranding can produce various
appearances. Mild inflammation may cause a subtle
hazy increased attenuation of the fat (ground-glass
like), increasing severity of the inflammation can
produce a reticular pattern, with more well-defined
linear areas of increased attenuation.
The underlying pathophysiologic process is increased
edema and engorgement of lymphatics.
What is the location of the fat stranding?
What other structures are involved in the process?
Are there other characteristic CT findings of the
diagnostic possibilities that suggest the most likely
“Disproportionate” Fat stranding—that is, much
greater than the degree of bowel wall thickening.
Suggests a narrower differential diagnosis:
diverticulitis, epiploic appendagitis, omental
infarction, and appendicitis.
Diverticula are small sacculations of mucosa
and submucosa through the muscularis of the
They develop where the nerve and blood
vessel pierce the muscularis between the teniae
coli and mesentery, an origin that accounts for
their propensity to bleed.
predominantly in the descending and sigmoid
colon but not in a rectum.
Diverticulitis occurs when the neck of a
diverticulum becomes occluded, resulting in
inflammation, erosion, and microperforation.
Microperforation results in pericolonic
inflammation that typically is more severe than
the inflammation of the colon.
CT finding - disproportionate paracolic fat
- comma sign
- engorgement of the mesenteric vessels, which
appears as the ―centipede sign‖.
Axial CT image of a man with left-sided diverticulitis shows severe pericolonic fat
stranding (arrowheads) that is greater than the degree of wall thickening of the
descending colon (curved arrow). A ―normal‖ diverticulum (open arrow) and a ill-
defined (fuzzy) diverticulum (solid straight arrow) are also seen.
Appendices epiploicae are pedunculated adipose
structures protruding from the external surface of
the colon into the peritoneal cavity.
Normally invisible on CT scans because they blend
with the surrounding fat unless they are
surrounded by ascites.
Each is supplied by one or two small end arteries
branching from the vasa recta longa of the colon.
Their limited blood supply, together with their
pedunculated shape and excessive mobility, make
appendices epiploicae prone to torsion and
Axial CT image shows normal appendices epiploicae
(arrows) of the sigmoid colon, which appear as fingerlike
projections of pericolic fat floating within ascites (∗).
Acute torsion of an appendage results in a focal
inflammatory process called epiploic
IMAGING - a paracolonic oval fatty mass
representing the infarcted or inflamed
- Well-circumscribed hyperattenuated rim that
surrounds the mass and represents the
inflamed visceral peritoneal lining
- High-attenuation central dot representing
engorged or thrombosed central vessels or
central areas of hemorrhage
enhanced CT image
shows an ovoid mass
(solid arrow) of fat
attenuation anterior to
the wall of the
descending colon. The
mass is surrounded by
a hyperattenuated rim
contains a central high-
attenuation dot (most
vessels). Note the
moderate fat stranding
(arrowhead) and mild
focal thickening of the
adjacent colonic wall
Segmental omental infarction typically occurs
on the right, a predilection that has been
attributed to an embryologic variant of the
Risk factors include obesity and recent surgery.
On CT scans, the infarcted omentum appears
as a large, cakelike, high-attenuation fatty mass
centered in the omentum.
Reactive bowel wall thickening may occur, but
the inflammatory process in the omentum
usually is disproportionately more severe.
Omental infarction and epiploic appendagitis
may have similar appearances on CT scans.
Axial contrast-enhanced CT image of a patient who presented with acute
right upper quadrant pain shows an inhomogeneous mass (arrow) in the
greater omentum, anterior to the transverse colon. Moderate adjacent
wall thickening is also evident (arrowhead). Diverticulitis was a
diagnostic consideration, but no diverticula were seen at CT.
obtained at a
than b) show
s round, high-
in the greater
anterior to and
effect on the
colon (arrow in
Is the most common cause of acute abdominal
pain that requires surgical intervention.
The primary pathogenic event in the majority
of cases is luminal obstruction caused by
fecaliths and lymphoid hyperplasia.
Once obstruction occurs, the continued
secretion of mucus results in elevated
intraluminal pressure and luminal distention,
with consequent venous engorgement, arterial
compromise, and tissue ischemia. Luminal
bacteria multiply and invade the appendiceal
wall, causing transmural inflammation.
CT Findings - Direct visualization of a dilated
(>6 mm in maximum diameter), fluid-filled
appendix is the most specific.
Other direct signs include an abnormally
thickened appendix, increased attenuation of
the appendix after contrast material
administration, and periappendicular fat
Secondary signs include appendicolith(s) or
thickening of the cecal apex (cecal bar sign).
d CT image
s). Note the
enhanced CT images (a
obtained at a higher
level than b) show the
of the dilated fluid-
filled appendix (white
fat stranding is severe
wall thickening of the
cecum (cecal bar sign)
(solid straight black
arrow) and also the
collection of contrast
agent (arrowhead sign)
(curved arrow) formed
as contrast material
funnels into the
partially coapted cecal
wall adjacent to the
appendicolith is also
seen (open arrow).
Bowel ischemia—Ischemia and infarction of the
gastrointestinal tract are a heterogeneous group of
disorders that have the unifying theme of hypoxia
of the small bowel or colon.
more common in the geriatric population,
especially in those with comorbid cardiovascular
CT can accurately show ischemic bowel segments
and often aids in determining the primary
CT Findings - wall thickening, which may be
hypoattenuating when there is submucosal
edema or hyperattenuating when there is
intramural hemorrhage from a reperfusion
Other findings are bowel dilatation, lack of
bowel wall enhancement, mesenteric fat
engorgement, ascites, pneumatosis and portal
There is abnormal
loop of ileum in right
lower quadrant (thick
arrows). Wall of
affected bowel is
thickened with low-
There is mild
stranding (thin arrows).
Filling defect in
thrombus. Rim of
wall, and fat
affected vessel is due
Complicated bowel obstruction, the
visualization of mesenteric fat stranding,
mesenteric fluid, and ascites can strongly
suggest the diagnosis of partial or transmural
If two of these three findings are present, the
specificity of this diagnosis is reported to be
single best predictor of ischemia is lack of
bowel wall enhancement.
sis of right
May cause fat stranding that is difficult to
differentiate from that seen with acute
The degree of bowel wall thickening can be a
helpful differential feature.
The bowel wall thickening is of soft-tissue
attenuation and does not display the target
sign or mural stratification signifying bowel
wall edema that is seen in inflammatory
processes or ischemia.
Focally thickened segment of sigmoid colon, which is of soft-tissue
attenuation, represents colon carcinoma with shouldering (short
arrow). There is moderate fat stranding in region of carcinoma,
secondary to perforation (long arrow).
Ulcerative colitis primarily affects the colon
(rectum and left colon), occasionally also
involving the terminal ileum with backwash
In contrast, Crohn disease usually affects the
small bowel (almost always the terminal ileum)
with or without colonic or anal involvement.
Bowel wall thickening is the most common CT finding.
Hazy (ground-glass) fat stranding in the mesentery results in a
Ulcerative colitis – diffuse symmetric colonic
- asymmetric inflammation along the mesenteric
- halo sign, which is due to the deposition of
submucosal fat that results in a low-attenuation ring
in the bowel wall.
Crohn disease - eccentric and segmental
- Pseudodiverticula develop on the antimesenteric border
of the colon opposite regions of fibrosis and scarring.
- Asymmetric Fibrofatty proliferation along the mesentric
border. - Creeping fat sign
in right iliac
Acute Pancreatitis - the pancreas appears
The pancreatic parenchyma may not enhance after
IV contrast administration in the setting of
pancreatic necrosis, which can be focal or diffuse.
In addition to fat stranding in the peripancreatic
tissues, other secondary findings include free fluid
in the paracolic gutters and pleural effusions.
There is severe peripancreatic fat stranding (thick arrows). Focal area of
parenchyma in pancreatic neck is not enhancing due to necrosis (thin
Severe fat stranding extends from peripancreatic region to left paracolic
gutter and anterior pararenal space (arrows). There is residual enhancing
pancreatic parenchyma in head of pancreas (arrowheads).
Acute pyelonephritis -
- The nephrographic phase of contrast enhancement is
- Typically ill-defined wedge-shaped areas of low density
are noted radiating from the papilla to the cortical
- These sites represent poor- or nonfunctioning
parenchyma due to vasospasm, tubular obstruction, or
- The striated nephrogram—bands of alternating high-
and low-density parallel to the axes of the tubules,
characteristic of acute pyelonephritis.
- Perinephric fat stranding is usually seen adjacent to the
abnormal areas because of an inflammatory reaction
with leukocytes forming an infection or infarction.
areas of low
density in upper
poles of both
g from papilla to
There is moderate right hydronephrosis (long arrows) and
mild perinephric fat stranding due to edema (short arrow).
Dilated right ureter with mild fat stranding (arrow)
arrows), and there
fat standing (thick
arrow). There is
idiopathic fibroinflammatory disorder that
affects the small-bowel mesentery.
Categorized as mesenteric panniculitis (chronic
inflammation), mesenteric lipodystrophy (fat
necrosis), and retractile mesenteritis (fibrosis).
sixth and seventh decades of life.
has a poorly understood association with
underlying malignancy and paraneoplastic
CT appearance - well-defined soft-tissue mass
containing areas of fat attenuation to an ill-defined
area of increased attenuation in the root of the
the changes of sclerosing mesenteritis occur
around the mesenteric vessels and do not displace
The CT appearance of a ―fat ring‖ sign—a thin
radiolucent rim of fat between the mesenteric
vessel and the mass in the mesentery.
loops of small
Involves terminal ileum and cecum (90% )
The disease causes circumferential thickening of
the bowel wall, with adjacent mild fat stranding
In advanced ileocecal disease, small-bowel loops
may become adherent in the right iliac fossa.
Peritoneal tuberculosis may affect the
peritoneal cavity, mesentery, and omentum.
The most frequent form (90% of cases) is the
―wet‖ type with ascites or pockets of loculated
The ―dry‖ type is characterized by fat
stranding in the mesentery, dense
adhesions, and adenopathy.
There is extensive fat stranding of greater omentum (long arrows). Peritoneum is thickened and
hyperenhancing (short arrows), and pockets of fluid are present (arrowheads)
There is moderate ascites (long arrow) and enhancement
of thickened peritoneum (short arrows).