Epiploic Appendagitis - Department of Radiology

G a s t r o i n t e s t i n a l I m a g i n g • R ev i ew
Almeida et al.
Imaging of Epiploic Appendagitis
Gastrointestinal Imaging
Review
Epiploic Appendagitis: An
Entity Frequently Unknown to
Clinicians—Diagnostic Imaging,
Pitfalls, and Look-Alikes
Ana Teresa Almeida1
Lina Melão
Barbara Viamonte
Rui Cunha
José Miguel Pereira
Almeida AT, Melão L, Viamonte B, Cunha R,
Pereira JM
OBJECTIVE. Epiploic appendagitis is an ischemic infarction of an epiploic appendage
caused by torsion or spontaneous thrombosis of the epiploic appendage central draining vein.
When it occurs on the right side of the abdomen, it can mimic appendicitis and right-sided diver­
ticulitis; whereas when it occurs on the left side of the abdomen, it is often mistaken for sigmoid
diverticulitis. The purpose of this article is to review the diagnostic imaging of this entity.
CONCLUSION. Epiploic appendagitis is self-limited and spontaneously resolves without
surgery within 5–7 days. Therefore, it is imperative for radiologists to be familiar with this entity.
E
Keywords: appendagitis, appendicitis, diverticulitis,
omental infarction
DOI:10.2214/AJR.08.2071
Received November 8, 2008; accepted after revision
April 12, 2009.
This article was prepared based on an educational
exhibit that won the Magna Cum Laude award at the
2007 annual meeting of the European Society of
Gastrointestinal and Abdominal Radiology.
1
All authors: Department of Radiology, Faculdade de
Medicina da Universidade do Porto, Hospital São João,
Alameda Professor Hernâni Monteiro, 4200-451 Porto,
Portugal. Address correspondence to L. Melão
(lina_melao@hotmail.com).
AJR 2009; 193:1243–1251
0361–803X/09/1935–1243
© American Roentgen Ray Society
AJR:193, November 2009
piploic appendages, also known
as epiploicae appendices, are
50–100 pedunculated fatty struc­
tures arranged in two separate
longitudinal rows next to the anterior and
posterior tenia coli over the external aspect
of the colon [1–4]. Epiploic appendages ex­
tend from the cecum to the rectosigmoid
junction and are covered by the peritoneum
[1, 4–8]. The greatest concentration of epi­
ploic appendages is in the cecum and sig­
moid colon but spares the rectum [5, 9]. Epi­
ploic appendages are between 1–2 cm thick,
0.5–5 cm long, and larger on the left side of
the colon than on the right side [3]. Each epi­
ploic appendage is supplied by one or two
small end arteries branching from the vasa
recta longa of the colon and is drained by a
tortuous vein passing through its narrow
pedicle [2–4]. Their limited blood supply, to­
gether with their pedunculated shape and ex­
cessive mobility, make epiploic appendages
prone to torsion and ischemic or hemorrhag­
ic infarction [1, 2, 4, 8, 10].
Epiploic Appendagitis
Appendagitis is a term denoting primary
or secondary inflammation of the epiploic
appendages [6].
Primary Epiploic Appendagitis
Primary epiploic appendagitis is an ischemic
infarction of an epiploic appendage and an
uncommon cause of abdominal pain that has
been recognized relatively recently [11]. Pri­
mary epiploic appendagitis is caused by epi­
ploic appendage torsion or spontaneous throm­
bosis of the epiploic appendage central
draining vein resulting in vascular occlusion
and focal inflammation [5–7, 12, 13]. In some
cases of epiploic appendagitis, inflammation
may be present without any vascular impair­
ment [6, 14, 15].
The reported age range for primary epi­
ploic appendagitis is 12–82 years, with a
peak in incidence in the fifth decade. Pri­
mary epiploic appendagitis is more common
in obese patients and women [3, 4]. Primary
epiploic appendagitis occurs more frequent­
ly in the sigmoid colon than in the cecum
or ascending colon and is uncommon in the
transverse colon [3, 5, 16]. Epiploic append­
ages may cause incarcerated hernia; a case
has been reported of an epiploic appendagitis
within an incisional hernia sac [10].
Primary epiploic appendagitis usually pre­
sents as an abrupt onset of focal abdominal
pain in the lateral lower quadrants, is nonmi­
gratory, and worsens with cough and abdomi­
nal stretching [2, 3, 11, 17]. Appetite and bow­
el function are usually unchanged; nausea and
vomiting are rare [6, 16]. On physical exami­
nation, the patient will present with localized
tenderness without significant guarding or ri­
gidity. The patient also may have a low-grade
fever [3, 18]. WBC count is usually normal or
slightly elevated [2]. Heavy exercise has been
reported as a predisposing factor [2, 4, 6].
Primary epiploic appendagitis is difficult
to diagnose clinically because of the lack
of pathognomonic clinical features and can
simulate a case requiring surgery [3, 4].
1243
Almeida et al.
should be used to confirm the fatty nature of
the lesion before making a definite diagnosis
of primary epiploic appendagitis. With the in­
creasing use of CT for assessing cases of acute
abdominal pain, the diagnosis of epiploic ap­
pendagitis is now more common [18, 19].
Primary epiploic appendagitis is self-lim­
ited in the majority of patients and spontane­
ously resolves within 5–7 days. Rarely, acute
epi­ploic appendagitis may result in adhesion,
bowel obstruction, intussusception, intraperito­
neal loose bodies, peritonitis, or abscess forma­
tion [3, 5]. Primary epiploic appendagitis does
not require surgery, and treatment is based on
the patient’s symptoms [4, 5, 7, 13, 15]. Misdi­
agnosis may lead to unwarranted surgery, med­
ical treatment, and hospitalization [4].
Fig. 1—54-year-old man with hepatic cirrhosis.
Unenhanced CT image shows several epiploic
appendices (arrowhead) outlined by ascites. Arrow
indicates normal central vein.
Right-sided primary epiploic appendagitis
is often confused with acute appendicitis or
right-sided diverticulitis; whereas left-sided
primary epiploic appendagitis is often con­
fused with sigmoid diverticulitis [3, 4, 18].
In the past, diagnosis of epiploic appendagi­
tis was often the result of an unexpected find­
ing during an exploratory laparotomy [3]. To­
day, this condition is usually diagnosed by
ultrasound or CT, with the latter more sensitive
and specific. Although ultrasound has the ad­
vantage of correlating the location of the lesion
with the location of maximum tenderness, CT
A
Secondary Epiploic Appendagitis
In secondary epiploic appendagitis, the
epiploic appendage is inflamed because of
another process, such as diverticulitis, appen­
dicitis, pancreatitis, or cholecystitis. Man­
agement of secondary epiploic appendagitis
is based on treatment of the primary abnor­
mality [1, 2, 4, 7].
Imaging Findings
The diagnosis of acute epiploic appendagi­
tis primarily relies on cross-sectional CT, al­
though ultrasound and MRI are occasionally
used [11, 19].
B
Fig. 2—Epiploic appendagitis in 46-year-old man.
A and B, Axial contrast-enhanced CT images show severe fat stranding (arrowhead) and fatty ovoid mass
(curved arrow) with hyperattenuated rim and central dot (thin straight arrow). Associated thickening of colonic
wall (open arrow) is mild.
1244
CT
In CT of a healthy patient, the epiploic ap­
pendages blend in with the surrounding peri­
colic fat but become apparent when surround­
ed by ascites (Fig. 1) or inflammation [3, 5,
8]. An infarcted or inflamed epiploic append­
age on CT appears as a 1–4 cm ovoid peri­
colic lesion with fat density surrounded by
inflammatory changes and abuts the anterior
colonic wall [1, 3, 5, 11, 15]. Primary epiploic
appendagitis may have a lobular appearance
because of two or more affected, contiguous
epiploic appendages with hyperattenuated
rings lying in proximity [19].
A 2–3 mm hyperdense rim surrounding
the ovoid mass on CT (hyperattenuating ring
sign) represents the inflamed visceral perito­
neal covering of the epiploic appendage and
is diagnostic of primary epiploic appendagi­
tis [13, 15]. The hyperdense rim surround­
ing the ovoid mass on CT corresponds to the
hypoechoic halo on ultrasound [13, 15, 19]
(Figs. 2–6). Thickening of the parietal peri­
toneum secondary to the spread of inflam­
mation may be observed [3, 5–7].
Fat stranding is more pronounced than
wall thickening because the paracolonic in­
flammatory changes are disproportionately
more severe than the mild local reactive thick­
ening of the adjacent colonic wall (Figs. 2–6).
Wall thickening of the adjacent side of the co­
lon is asymmetric [1, 4, 8] (Figs. 2 and 3).
A central, hyperattenuating, ill-defined
round area (“central dot sign”) or a longitu­
dinal linear area corresponds to engorged or
thrombosed central vessels or central areas
of hemorrhage or fibrosis (Figs. 2–4). Al­
though the presence of a central dot or lin­
ear area is useful for diagnosis, their absence
does not exclude the diagnosis of acute epi­
ploic appendagitis [4–6, 11, 19, 20].
The central dot may have high attenuation
because the infarcted tissue tends to calcify.
Calcification may be eggshell in shape and
may become detached and appear as a peri­
toneal loose body in the abdominal cavity [1,
3, 16, 21]. The calcified tissue may reattach
itself to a surface, such as the lower aspect of
the spleen, in which case it is called a “parasit­
ized epiploic appendage” [3]. The smooth sur­
face and calcified consistency of the epiploic
appendage help to distinguish it from a meta­
static lesion (Fig. 7).
Ultrasound
At the site of maximum tenderness, a non­
compressible hyperechoic small ovoid or
round solid mass of adipose tissue is seen be­
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Imaging of Epiploic Appendagitis
Fig. 3—Primary epiploic appendagitis in 23-year-old
man with clinical diagnosis of presumed colonic
diverticulitis. Axial contrast-enhanced CT scan
shows pericolonic fatty lesion surrounded by
hyperattenuating ring (thick arrow) containing central
hyperattenuating area (thin arrow) corresponding to
thrombosis and hemorrhagic changes and very mild
thickening of colonic wall (open arrow).
Fig. 4—Acute epiploic appendagitis with
hyperattenuating center in 31-year-old woman. Axial
contrast-enhanced CT image shows lesion (arrow)
that abuts sigmoid colon and has central focal area of
hyperattenuation with surrounding inflammation.
Fig. 5—40-year-old man with acute epiploic
appendagitis with hyperattenuating ring sign
(thick arrow) adjacent to left colon without
significant involvement of colonic wall. Severe and
disproportionate fat stranding (thin arrow) is seen
nearby.
Fig. 6—Acute epiploic appendagitis (arrow) with
hyperattenuating ring sign adjacent to sigmoid colon
without significant involvement of colonic wall in
52-year-old man.
Fig. 7—CT image shows small calcified body (arrow)
adjacent to normal epiploic appendices, probably
residual to anterior epiploic appendagitis in 59-yearold man.
Fig. 8—Sonogram in 22-year-old man shows
hyperechoic small mass (asterisk) surrounded
by hypoechoic border (arrow) corresponding to
hyperattenuating ring on CT scans at site of maximum
tenderness, located anteriorly between colon and
abdominal wall.
tween the colon and the abdominal wall in
the anterior or anterolateral compartment of
the abdomen [1, 6, 22] (Fig. 8). In most cas­
es, a mass effect is seen either on the adjacent
bowel or in the anterior parietal peritoneum.
Changes to the colonic wall are not seen [12].
The lesion is adherent to the colonic wall, is
frequently surrounded by a hypoechoic bor­
der (Fig. 8), and does not have central blood
flow on Doppler ultrasound [4, 12]. The ab­
sence of a Doppler signal because of a lack
of blood flow as a result of torsion in epiploic
appendagitis is a useful finding to differen­
tiate epiploic appendagitis from acute diver­
ticulitis [12].
images, confirming the fatty nature of the le­
sion [23].
In epiploic appendagitis, the thin periph­
eral rim and the perilesional inflammatory
changes appear hypointense on T1-weighted
imaging, appear hyperintense on T2-weight­
ed imaging, and show marked enhancement
on contrast-enhanced T1-weighted fat-sup­
pressed images, whereas the central drain­
ing vein usually has low signal on both T1weighted and T2-weighted imaging [23].
Diverticulitis
Diverticula are herniations of the mucosa
and submucosa through the muscular layers of
the bowel wall in areas of bowel wall weak­
ness (between the mesenteric and antimes­
enteric taeniae) and high pressure gradient
(caused by dehydrated stools) [8, 24]. Diver­
ticula occur at the point where blood vessels
(vasa recta) penetrate the colon wall [24].
Diverticulitis occurs when a diverticu­
lum becomes obstructed, with subsequent
focal inflammation, diverticular distention,
localized ischemia, and perforation [24].
Typically, perforation of the colonic wall is
confined and restricted, leading to peridi­
verticular and extracolonic inflammation
that is more severe than the inflammation of
the colon itself [8]. However, the course of
the disease may be complicated by abscess
formation, hemorrhage, pneumoretroperito­
neum, fistula formation, and postinflamma­
tory stenosis.
MRI
The involved epiploic appendage is hyper­
intense on unenhanced T1-weighted imaging
but is slightly less intense than normal peri­
toneal fat. Epiploic appendages show marked
loss of signal on fat-suppressed T2-weighted
AJR:193, November 2009
Differential Diagnosis
In epiploic appendagitis, there is much
more fat stranding than bowel wall thicken­
ing. In patients with acute abdominal pain,
the finding of fat stranding that is dispropor­
tionate suggests a relatively narrow differ­
ential diagnosis: diverticulitis; omental in­
farction; appendicitis; and, less commonly,
mesenteric panniculitis and primary tumors
and metastases to the omentum.
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Almeida et al.
Diverticula can be found anywhere in the
colon, but the majority are located in the dis­
tal descending and sigmoid colon; hence,
most cases (95%) of diverticulitis are located
in the left side of the abdomen. A minority of
diverticula (5%) are located on the right side
of the abdomen, which for unknown reasons
has a predilection for patients of Asian de­
scent. The transverse colon is rarely affect­
ed, whereas the rectum is completely spared
from diverticula formation [8].
The most common CT finding of acute di­
verticulitis is paracolic fat stranding. Other
typical CT findings include an ill-defined or
blurry diverticulum in the region where the
fat stranding is most pronounced (Figs. 9 and
10); mild wall thickening (usually < 5 mm),
commonly more pronounced on the side of
the offending diverticulum and usually af­
fecting a large colonic segment greater than
5 cm (Figs. 9 and 10); thickened base of
the sigmoid mesocolon with fluid (“comma
sign”) (Figs. 9 and 10); and engorged ves­
sels supplying the affected segment (“centi­
pede sign”) [8]. Other findings detected by
CT include pericolic abscess, small-bowel
obstruction, free intraperitoneal or extraperi­
toneal gas, colovesical fistula, thrombosis of
the mesenteric or portal veins caused by pyo­
phlebitis, and hepatic abscess formation. In
some instances, small localized collections
of gas are identified adjacent to the colonic
wall and indicate localized pericolic perfora­
tion [17] (Figs. 11 and 12). In cases of com­
plicated diverticulitis, surgical management
may be required.
Features that help discern the differential
diagnosis—Although their clinical manifes­
tations are similar, acute epiploic appendagi­
tis tends to occur in younger patients, where­
as acute diverticulitis frequently affects older
patients (> 50 years). Patients with divertic­
ulitis are more likely to experience nausea,
vomiting, fever, rebound tenderness, and
more diffuse lower abdominal pain. Only a
minority (7%) of patients with acute epiplo­
ic appendagitis have leukocytosis, whereas
most patients with acute diverticulitis have
an elevated WBC count [5].
In cases of acute epiploic appendagitis, the
involved colonic segment is short; however, in
cases of acute diverticulitis, a lengthy segment
of thickened colonic wall is a typical CT fea­
ture [8].
The classic complications of diverticuli­
tis (extramural abscesses, sinus tract and fis­
tula formation, bowel obstruction, perfora­
tion, and peritonitis) are rare in the setting
1246
A
B
Fig. 9—61-year-old man with diverticulitis.
A and B, Axial contrast-enhanced CT images show mild stranding of pericolonic fat (asterisk). Fuzzy (thick
arrow, B) and normal diverticula (thin arrows) are seen.
A
B
Fig. 10—52-year-old woman with diverticulitis.
A and B, Transverse contrast-enhanced CT images show engorgement of vasa recta feeding sigmoid colon
(“centipede sign,” open arrow, B). Notice mild wall thickening of colon, with fuzzy (curved arrow, A) and normal
(thin arrows) diverticula and fluid by side of root of sigmoid mesentery (arrowhead, B). “Comma sign” (thick
arrow, A) and disproportionate fat stranding (asterisk, A) are also seen.
of acute epiploic appendagitis [5, 17] (Figs.
11 and 12).
Features that complicate the differential
diagnosis—Both epiploic appendagitis and
acute diverticulitis frequently present with
a sudden focal left-sided tenderness. More­
over, the two conditions can be seen simul­
taneously because the inflammation from an
acute diverticulitis may extend to involve the
epiploic appendages [4, 5, 7] (Fig. 12).
Omental Infarction
The greater omentum consists of a fourlayered fold of peritoneum that covers the co­
lon and small bowel in the peritoneal cavi­
ty, acting as a barrier to generalized spread
of intraperitoneal infection or tumor. It con­
tains fat and vascular structures (Fig. 13).
Omental infarctions are rare because abun­
dant collateral vessels perfuse the omentum
[25]. The cause of omental infarction is un­
clear but may be similar in pathophysiology
to the cause of primary epiploic appendagitis
[9]. Omental infarction occurs when there is
an interruption of arterial blood supply to the
omentum, possibly because of omental torsion,
venous insufficiency due to trauma, or sponta­
neous thrombosis of the omental veins [5, 26].
Right-sided epiploic vessels are involved in
90% of the cases and are thought to be caused
AJR:193, November 2009
Imaging of Epiploic Appendagitis
Fig. 11—45-year-old man with intraabdominal
abscess. Contrast-enhanced CT image shows
intraabdominal fluid–air collection (arrow).
Diverticulitis was proven at surgery.
by the omentum being longer and more mobile
on the right side [21]. Precipitating factors in­
clude obesity, recent abdominal surgery, stren­
uous activity, congestive heart failure, digitalis
administration, and abdominal trauma [5, 12,
27]. However, most cases of omental infarc­
tion are idiopathic [16] (Fig. 13).
Omental infarctions are usually localized
to the right upper and lower quadrants and
clinically mimic cholecystitis and appendici­
tis, respectively [16, 26, 28]. A few cases of
left-sided omental infarction have also been
described [28].
Omental infarction more commonly af­
fects elderly obese patients, with a slight pre­
dilection for men [16]. Omental infarction
usually presents with acute abdominal pain
with normal or mildly elevated WBC count.
Other presenting symptoms include nausea,
vomiting, anorexia, diarrhea, and fever [21].
CT findings of omental infarction range
from a subtle, focal, hazy soft-tissue infil­
tration of the omentum [25, 29] to a solitary
large, cakelike, nonenhancing, heteroge­
neous, and high-attenuating fatty mass cen­
tered in the great omentum [8, 13, 21] (Figs.
14–17). Omental infarctions are usually lo­
cated in the right upper or lower quadrants,
deep in relation to the abdominal wall, ante­
rior to the transverse colon, or anteromedial
to the ascending colon. Colonic involvement
depends on the anatomic location of the in­
farcted omentum relative to the colon [8, 11,
13, 26] (Figs. 14–16). Reactive bowel wall
thickening may occur, although the inflam­
matory process in the omentum is usually
disproportionately more severe [8, 21, 26].
Omental torsion is implicated as a cause of
omental infarction when a whirled pattern of
concentric linear strands is seen on CT [21].
In most cases of omental infarction, the
process is self-limited, but surgery may be
AJR:193, November 2009
A
B
C
D
Fig. 12—52-year-old man with left-side diverticulitis.
A–D, Contrast-enhanced CT images (A and C) with magnified images (B and D) show intraabdominal free air in
large quantities (asterisk, A and C). Severe fat stranding, comma sign (curved arrow, A and B), and diverticula
(thin arrows, A and B) are seen. Note intraabdominal fluid–air collection (open arrow, C and D) and secondary
epiploic appendagitis (solid arrow, C and D).
indicated if symptoms persist or an associ­
ated abscess develops [27].
Features that help discern the differential
diagnosis—Unlike acute epiploic appendagi­
tis, which predominantly affects adults (> 20
years), omental infarction can occur in pedi­
atric patients (15% of cases) [5].
On CT, omental infarction lacks the hy­
perattenuating ring and central dot seen in
epiploic appendagitis [2, 5, 21, 28].
The focal lesion in acute epiploic ap­
pendagitis is often less than 5 cm long, may
have a lobular appearance, and is frequently
found adjacent to the sigmoid colon. The le­
sion in omental infarction is larger than that of
epiploic appendagitis (averaging a diameter
of up to 7 cm), cakelike, centered in the omen­
tum, and commonly located medial to the ce­
cum or the ascending colon [4–6, 19, 21].
The pain in acute epiploic appendagitis is
typically in the inferior abdomen, whereas
the pain in omental infarction is more com­
mon in the right side of the abdomen.
Features that complicate the differential
diagnosis—The CT findings in both epiplo­
ic appendagitis and omental infarction may
Fig. 13—Normal greater omentum in 63-year-old
woman. Axial contrast-enhanced CT image shows
normal layer of fat attenuation between transverse
colon and anterior abdominal wall (arrow).
overlap and the two entities cannot be differ­
entiated. Nevertheless, the clinical relevance
of such differentiation is limited because
both conditions are self-limited and tend to
resolve spontaneously [4, 28]. Treatment is
conservative unless the infarcted omentum
becomes infected [2].
Because they have the same common
denominator of spontaneous fatty tissue
1247
Almeida et al.
A
B
B
C
D
Fig. 14—Acute omental infarction in 68-year-old woman.
A–C, Ultrasound images show hyperechoic, nonmobile mass (arrows, A and C) located between anterior wall
and colon.
D, Axial contrast-enhanced CT image shows oval lesion with heterogeneous attenuation (arrow) separated
from colon in right lower quadrant.
Fig. 15—Omental infarction in 71-year-old man.
CT image shows heterogeneous, cakelike fatty
mass centered in omentum located in right upper
quadrant anterior to and continuous with ascending
colon (arrow). Reactive bowel wall thickening
(arrowhead) is seen.
Fig. 16—Omental infarction in 65-year-old man.
CT image shows solitary heterogeneous and highattenuation fatty mass centered in omentum (arrow)
located deep in relation to rectus abdominis muscle
and anterior to transverse colon.
necrosis, epiploic appendagitis and omen­
tal infarction have recently been proposed
to be regrouped under the same new term,
“intraabdominal focal fat infarction” or
“IFFI,” to stress that the differentiation is
not clinically important and that the man­
agement of the two entities is conservative
[9, 30].
1248
Appendicitis
In the Western world, appendicitis is the
most common cause of acute abdominal pain
that requires surgical intervention [31, 32].
The cause in the majority of cases is obstruc­
tion of the lumen of the appendix second­
ary to fecaliths, lymphoid hyperplasia, for­
eign bodies, parasites, and tumors [33]. After
mechanical obstruction, the continued secre­
tion of mucus results in luminal distention,
venous engorgement, arterial compromise,
and tissue ischemia. Luminal bacteria multi­
ply and invade the appendiceal wall, causing
transmural inflammation. Appendiceal in­
farction, microperforation, and extension of
inflammation to the parietal peritoneum and
adjacent structures are possible sequelae of
appendicitis [8, 31, 33].
Appendicitis can affect all ages, although
it is relatively rare at extremes of age, with
the greatest incidence in the second decade
of life [32, 33]. Appendicitis usually presents
as a periumbilical pain of less than 5 days
in duration and migrates to the right lower
quadrant, associated with peritoneal irrita­
tion, anorexia, nausea, vomiting, diarrhea,
and temperature greater than 37.5°C [34].
The WBC count may be elevated, but this is
not seen in all cases of appendicitis.
Acute appendicitis presents on CT imag­
es as a thick fluid-filled appendix (> 6 mm
outer-to-outer wall), with intramural gas, ap­
pendiceal wall thickening (wall thickness
≥ 3 mm), and a stratified appearance that
may hyperenhance after contrast material
administration [31, 35]. Endoluminal appen­
dicoliths are present in one third of patients
with appendicitis; their presence increas­
es the likelihood of appendiceal perforation
[31, 33]. Occasionally, an appendicolith may
be identified in an otherwise normal-appear­
ing appendix [27].
Other associated CT signs of appendicitis
are adjacent bowel wall thickening, cecal apical
thickening (“cecal bar” and arrowhead signs),
adjacent fat stranding, right lateral conal thick­
ening, the presence of an abscess, and lymph­
adenopathy [8, 31, 32, 34] (Figs. 18 and 19).
Periappendicular fat stranding is typical­
ly mild to moderate, but the diagnosis of ap­
pendicitis is strongly implicated when severe
fat stranding is found in the absence of sub­
stantial cecal or ileal thickening. A careful
search for a thickened or focally perforated
appendix will often confirm the diagnosis of
appendicitis [8].
Features that help discern the differential
diagnosis—Appendicitis affects all ages,
AJR:193, November 2009
Imaging of Epiploic Appendagitis
Fig. 17—Omental infarction in 51-year-old man.
Transverse contrast-enhanced CT image shows
inhomogeneous, ill-defined ovoid-shaped fatty mass
(thin arrow) centered in greater omentum distant
from descending colon wall (thick arrow).
A
A
B
Fig. 18—28-year-old man with appendicitis.
A and B, Transverse unenhanced CT images show thickened appendix (short arrow) surrounded by marked fat
stranding (asterisk). Note high-density appendicolith (long arrow, B).
B
C
Fig. 19—24-year-old man with appendicitis.
A, Axial contrast-enhanced CT image shows dilated appendix with abnormally enhanced wall (arrow).
B and C, Longitudinal (B) and transverse (C) ultrasound images show enlarged (12 mm) appendix (arrow, C)
that is noncompressible with hyperreflective adjacent fat (asterisk, C) suggesting local inflammation. Line in B
indicates thickness of appendix.
D, CT scan after IV and oral contrast administration in a different patient (41-year-old man) with appendicitis
shows thickened appendiceal wall with wall enhancement (arrow) and fat stranding. Note enlargement of right
vesical wall (arrowhead) caused by inflammatory process.
unlike acute epiploic appendagitis, which
predominantly affects adults (> 20 years).
Appendicitis has a more typical clinical pre­
sentation with periumbilical pain migrating
to the right lower quadrant and is associat­
ed with anorexia and nausea. Patients with
acute epiploic appendagitis usually do not
present with significant guarding or rigid­
ity on physical examination. Most patients
with acute appendicitis have an elevated
WBC count, whereas only a minority of pa­
tients with acute epiploic appendagitis have
leukocytosis.
A definitive CT diagnosis of appendicitis
can be made with the identification of an ab­
normal appendix or a calcified appendicolith
AJR:193, November 2009
in association with pericecal inflammation
[33]. Doppler ultrasound shows increased
blood flow in contrast to absent blood flow in
epiploic appendagitis [4, 12, 20].
Features that complicate the differential
diagnosis—Classic presentation of acute
appendicitis occurs in only 50–60% of pa­
tients, and the diagnosis may be missed or
delayed in cases without the classic presen­
tation [33]. In cases of perforated appendi­
citis, with peritonitis and abscess formation,
the appendix may be difficult to see on im­
aging studies [8]. In early or mild appendici­
tis, the appendix may remain normal in size
[35], and inflammatory stranding of the peri­
appendicular fat may be the only finding.
D
Mesenteric Panniculitis
Mesenteric panniculitis is a subgroup of
sclerosing mesenteritis, consisting of nonspe­
cific chronic inflammation and fibrosis of the
fatty tissue of the bowel mesentery. Depend­
ing on the predominant tissue type in the mes­
enteric lesion, sclerosing mesenteritis can be
categorized into three subgroups: mesenter­
1249
Almeida et al.
Fig. 20—Mesenteric panniculitis in 57-year-old woman.
A and B, Axial contrast-enhanced CT scans for
colon cancer follow-up show soft-tissue nodules
corresponding to enlarged lymph nodes within
inflamed mesenteric fat (arrowheads).
A
B
Fig. 21—Well-differentiated liposarcoma in 61-yearold man.
A and B, Contrast-enhanced CT scan (A) and
ultrasound image (B) show well-circumscribed fatty
mass (thick arrow) with enhancing capsule and
internal septa that displaces mesenteric vessels (thin
arrow, A).
A
B
Fig. 22—Peritoneal carcinomatosis in 52-year-old
man.
A and B, Axial contrast-enhanced CT scans show
omental caking (asterisks, B), omental nodules
(arrows), and small-volume ascites from gastric
carcinoma.
A
B
ic panniculitis if inflammation pre­dominates
over fibrosis, mesenteric lipodystrophy if fat
necrosis is the predominant process, and re­
tractile mesenteritis if fibrosis and retraction
predominate [5, 36, 37]. Retractile mesenteri­
tis is considered the final, more invasive stage
of mesenteric panniculitis complicated by fi­
brosis and retraction [36]. Progression from
mesenteric panniculitis to retractile mesen­
teritis is difficult to predict but fortunately is
rare [29]. In most patients, the condition con­
sists of a mixture of chronic inflammation, fat
necrosis, and fibrosis [8].
Most cases of mesenteric panniculitis occur
in middle or late adulthood (mean age, ~ 60
years), with a slight male predominance [5,
37]. Mesenteric panniculitis may be entirely
asymptomatic, but clinical manifestations
may be related to the inflammation or its
mass effect and include acute abdominal
pain, fever, nausea, vomiting, diarrhea, and
weight loss [5, 36, 37]. Mesenteric panniculi­
tis can be found in 0.6% of all patients under­
going abdominal CT for various indications.
The pathogenesis is uncertain but can be as­
sociated with autoimmune disease, a parane­
oplastic process, trauma, previous surgery,
drug-induced disease, infection, and throm­
bosis of mesenteric vessels [37].
Mesenteric panniculitis mainly involves
the mesentery of the small bowel, especially
at its root [25, 37, 38]. The CT findings of
mesenteric panniculitis include a focal area of
increased attenuation within the mesenteric
fat surrounded by a thin pseudocapsule that is
usually oriented to the left side [5, 37, 38].
Mesenteric panniculitis surrounds the mesen­
teric vessels and shows some regional mass
effect by local displacement of small-bowel
loops. The small soft-tissue nodules associat­
ed with mesenteric panniculitis are thought to
correspond to lymph nodes scattered within
the mesenteric mass, usually less than 5 mm
in diameter [8, 26]. The “fat-ring sign” ap­
pears as low-density fat that surrounds ves­
sels and nodules within the mesenteric mass
1250
and represents preservation of normal fat
density because of unaffected noninflamed
fat [25, 26, 37, 38] (Fig. 20). The fat-ring sign
is suggestive of mesenteric panniculitis but is
nonspecific because it can be found in other
entities such lymphoma [26]. Areas of fibro­
sis within the inflammation appear as linear
bands of soft-tissue attenuation, resulting in
spiculation that may be mistaken for a neo­
plastic process [5]. Calcification is uncom­
mon and may be related to the fat necrosis
[36]. The major complications of mesenteric
panniculitis are related to the progressive fi­
brosis that may lead to shortening of the mes­
entery, compression of the mesenteric ves­
sels, and bowel-loop narrowing [5, 37].
Some features can help discern the dif­
ferential diagnosis. Mesenteric panniculitis
is not an acute abdominal condition and ap­
pears as a larger lesion. It is most commonly
located in the root of the small-bowel mes­
entery that does not abut the colonic wall.
Acute epiploic appendagitis, as the name im­
AJR:193, November 2009
Imaging of Epiploic Appendagitis
plies, is an acute disease seen as a small focal
lesion anterior or anteromedial to the colon,
abuts the colon wall, and does not involve the
small-bowel mesentery [5].
Primary Tumors and Metastases
There are many other possible causes for a
CT finding of a fatty mass or masslike lesion
in the abdomen, such as liposarcoma (Fig.
21), dermoid and carcinoid tumor, lipoma,
and omental metastases (Fig. 22).
Omental metastases can present as soft-tis­
sue implants on peritoneal surfaces. “Omen­
tal cake” is the replacement of the omental fat
by tumor infiltration and on CT appears as a
thick, confluent soft-tissue mass closely ad­
herent to the ventral surface of the transverse
colon in the mid abdomen [25]. The presence
of ill-defined lesion margins, numerous le­
sions, a lesion centered in the omentum, and a
history of primary neoplasm are useful for di­
agnosing omental metastasis [5] (Fig. 22). In
patients with known malignancy, the diagno­
sis of acute epiploic appendagitis should only
be made if there is a presentation with acute
abdominal pain and no CT evidence of perito­
neal metastatic disease elsewhere [2].
Conclusion
Epiploic appendagitis is self-limiting, and
the appropriate management is conservative.
In our experience, many clinicians are not
familiar with this entity, and the radiologist
can provide guidance for supportive manage­
ment. Therefore, a noninvasive diagnosis of
this relatively rare cause of acute abdomen is
important for selecting the appropriate mode
of management and preventing unnecessary
hospital admission and surgery.
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