Dr. Baldwin is a Radiologist at South Shore Hospital, Weymouth, MA; Dr. Genant is an Associate Professor of Radiology at San Francisco Medical Center, San Francisco, CA; Dr. Braver
is the Director of Gastrointestinal Radiology at Brigham & Women’s
Hospital and an Assistant Professor at Harvard Medical School, Boston,
MA; and Dr. Mortele is the Director of the Division of Clinical
MRI at Beth Israel Deaconess Medical Center, Boston, MA, and the
Associate Professor of Radiology at Harvard Medical School, Boston, MA.
names of many classic radiologic signs derive from analogues to objects
commonly encountered in everyday life; eg, the “comb” sign. The use of
familiar objects to describe visual findings enables radiologists both
to arrive at a correct diagnosis and to effectively convey such
diagnostic findings to clinicians.
appendages epiploicae are peritoneal pouches containing pericolonic fat
connected to the serosal surface of the colon by a vascular stalk
composed of 2 feeding arteries and one draining vein. These appendages
are found in 2 rows. One row is medial to the tenia libera; the other
lateral to the tenia omentalis. Torsion of the appendages epiploicae
with resulting vascular occlusion is believed to be the cause of
epiploic appendagitis. The most common sites for epiploic appendagitis
are adjacent to the sigmoid colon, descending colon, and right
The hyperattenuation “ring sign” is a
classic finding on CT examinations in epiploic appendagitis. It consists
of a thin, round, or oval high-attenuation ring representing thickened,
inflamed visceral peritoneum surrounding the torsed epiploic appendage
(Figure 26).75 Internally, the high-attenuation ring contains
fat and often a central dot of high attenuation that represents the
thrombosed central vein.76
Coffee bean sign
The “coffee bean” sign is seen on supine plain films of the abdomen in approximately 80% of cases of sigmoid volvulus.77
The appearance of the coffee bean is created by the dilated lateral
walls of the sigmoid colon forming the outer walls of the coffee bean
and the closely apposed medial walls forming the cleft of the coffee
bean (Figure 27).78 This gas-filled segment of bowel arises
from the pelvis and may fill the entire abdomen. Its apex often extends
superior to the 10th thoracic vertebral body and the apex can be located to the left or right of midline.79,80
cecal volvulus can appear very similar to a sigmoid volvulus; however, a
cecal volvulus should have only one air-fluid level, whereas a sigmoid
volvulus may demonstrate two air-fluid levels. A distended, transverse
colon can also mimic a sigmoid volvulus. This dilated bowel, however,
does not arise from within the pelvis and it extends superiorly in a
U-shaped configuration.81 The coffee bean sign has also been used to describe small-bowel, closed-loop obstructions.82
“sandwich” sign describes the appearance of mesenteric lymphadenopathy
encasing enhancing mesenteric vessels and bowel on contrast-enhanced CT
studies. The enhancing, encased vascular structures represent the
sandwich filling while the soft-tissue attenuation, mesenteric
lymphadenopathy comprises the bun (Figure 28). This classic CT sign can
also be seen on ultrasound in the presence of mesenteric
The sandwich sign is specific for
mesenteric lymphomas. Although many disease processes may cause
mesenteric lymphadenopathy, only lymphoma results in the large, bulky
lymphadenopathy that results in the sandwich sign.84
lymphoproliferative disorder (PTLD) can also cause a sandwich sign in
patients who have received solid organ or bone marrow transplants. PTLD
is a lymphoproliferation caused by the Ebstein-Barr virus in
classic plain film finding represents gas-containing fissures within
gallstones. Bauer first described this phenomenon in 1931.86
These gas-containing pockets are seen as stellate radiolucencies in the
right upper quadrant. The lucencies frequently form a triradiate
pattern, thus this finding is referred to as the “Mercedes-Benz” sign
The radiolucent fissures are most commonly widest
centrally and radiate peripherally like the points of a star. Five
radiolucent fissures have rarely been observed in gallstones. The radial
fissures tend to be of the same length and extend to the mid-point of
the sides of faceted stones. They do not extend to the periphery and are
mainly located within the central two-thirds of the calculi.87
Central dot sign
“central dot” sign is seen in dilated intrahepatic biliary ducts (IBD).
This sign describes the presence of a punctate dot of contrast
enhancement within the dilated IBDs. The central dot sign is produced by
enhancing branches of the portal vein surrounded by dilated IBDs
(Figure 30). This sign is highly suggestive of Caroli disease.88,89
disease represents the Type V Todani choledochal cyst; communicating
cavernous ectasia of the IBDs. It is a rare, autosomal recessive
disorder that affects the normal embryologic remodeling of the large
intrahepatic ducts. This results in a cystic dilatation of the IBDs.
Abnormal development of the small interlobular bile ducts results in
congenital hepatic fibrosis. If both the large and small ducts are
affected and both features of congenital hepatic fibrosis and Caroli
disease are present, this entity is termed Caroli
Hegner first described the radiographic appearance of emphysematous cholecystitis on plain radiographs in 1931.93
This rare form of acute cholecystitis most commonly affects men between
the ages of 50 and 70 who have underlying diabetes mellitus and/or
atherosclerotic disease.94 Vascular compromise of the cystic artery is thought to play a key role in the etiology of this pathologic process.95
(US) may show small echogenic foci of gas rising toward the
nondependent portion of the gallbladder lumen. These rising foci can
mimic the effervescing bubbles one sees in a glass of champagne (Figure
31). The champagne sign is a specific, but insensitive finding in
emphysematous cholecystitis. Surrounding pericholecystic gas may obscure
the gallbladder lumen from evaluation.96
Pearl necklace sign
represents the presence of intramural diverticula of the gallbladder
mucosa, the Rokitansky-Aschoff sinuses, within a thickened,
hypertrophied mucosa and muscularis propria of the gallbladder wall.97,98
“pearl necklace” sign was described when the Rokitansky-Aschoff sinuses
within the thickened gallbladder wall filled with contrast and
opacified during drip-infusion cholecystographic studies, giving a
beaded necklace appearance (Figure 32).99 However, successful
opacification of the Rokitansky-Aschoff sinuses was seen in only
approximately 5% of drip-infusion cholecystograms. The pearl necklace
sign is currently much more reliably seen on heavily T2-weighted, fast
spin-echo (FSE) magnetic resonance cholangiopancreatography images as a
curvilinear arrangement of multiple rounded foci of hyperintense T2
signal within the thickened wall of the gallbladder.100
can also be demonstrated on postcontrast CT images. The “rosary sign”
is created on postcontrast CT images by the enhancement of the
proliferative mucosal epithelium lining the Rokitansky-Aschoff sinuses
surrounded by the unenhanced, hypertrophied muscularis layer of the
gallbladder wall.101 The enhancement of multiple, rounded
sinuses within the thickened gallbladder wall produces the rosary bead
appearance (Figure 33).102
Double duct sign
The “double duct” sign was initially described through the use of endoscopic retrograde cholangiopancreatography (ERCP).103
To date, this sign has also been described using magnetic resonance
cholangiopancreatography (MRCP), multidetector CT (MDCT), and ultrasound
(US).104-107 The double duct represents simultaneous
dilatation of the common bile duct and the pancreatic duct occurring
secondary to contiguous distal biductal stenosis (Figure 34).108
causative narrowing of the common bile and pancreatic ducts most
commonly occurs due to contiguous obstruction or encasement by a
carcinoma of the head of the pancreas or the ampulla of Vater. Other
malignant etiologies of biductal dilatation are metastases, lymphoma,
and cholangiocarcinoma of the distal common bile duct.109
Various benign etiologies have also demonstrated the double duct sign.
These include chronic pancreatitis and ampullary stenosis. Thus, the
double duct sign is highly suggestive of, but not specific for,
carcinoma of the head of the pancreas.110
“telltale triangle” sign represents a small amount of free
intraperitoneal gas observed on supine cross table lateral radiographs
of the abdomen. The crosstable lateral view is extremely sensitive for
detecting small amounts of pneumoperitoneum because it utilizes
horizontal X-ray beams directed tangentially to intraperitoneal
collections of free air.111
The base of the telltale
triangle sign is classically formed by free air abutting the anterior
parietal peritoneum, with the apex of the triangle pointing posteriorly,
formed by free air interposed between 2 or more loops of gas-filled
bowel adjacent to the anterior abdominal wall (Figure 35).112
Miller first described the “football” sign in 1960.113
This sign represents a large ovoid radiolucency extending in a
cephalocaudal axis within the abdomen. The football sign is seen on
supine abdominal plain radiographs in severe pneumoperitoneum;114
most frequently in infants with spontaneous or iatrogenic gastric
perforation. Only 2% of adults with pneumoperitoneum demonstrate the
Abundant free gas within the
abdominal cavity collects anterior to the viscera and creates a sharp
interface with the parietal peritoneum, thus outlining the peritoneal
cavity. This gaseous interface with the peritoneum creates the ovoid
shape of an American football (Figure 36). The massive pneumoperitoneum
may outline the falciform ligament in the right upper quadrant. The gas
may also outline the median umbilical ligament that is composed of the
urachal vestige. The medial and lateral umbilical folds may also be
outlined. These folds are composed of the umbilical and inferior
epigastric vessels, respectively, that form the seams of the football.113,116
“Rigler ” or “bas-relief” sign is also seen on supine plain radiographs
of the abdomen in cases of pneumoperitoneum. Rigler first described
this finding in 1941.117 This sign is seen only in the
presence of moderate to large amounts of pneumoperitoneum. With a
prevalence of 32%, the bas-relief sign follows right upper-quadrant,
subdiaphragmatic free air as the second most common sign of
pneumoperitoneum on supine plain radiographs. 115
bas-relief sign represents the visualization of both the luminal and
serosal surfaces of the bowel wall due to the accumulation of free
intraperitoneal gas between bowel loops (Figure 37).118 A
variant of the Rigler sign occurs when only the external surface of the
bowel wall is visualized due to the presence of fluid within the bowel
The bas-relief sign can be mimicked by two
closely contiguous loops of bowel. In this case, intraluminal gas in one
loop can appear to outline the wall of an adjacent loop.115
Residual oral contrast from a recent CT study can also increase the
apparent bowel-wall attenuation and create a pseudo-Rigler sign.119
Mach bands can also create a false positive bas-relief sign because
there is the perception of a line at the interface of two differing
“cupola sign” represents an inverted cup-shaped lucency seen within the
upper abdomen on supine plain radiographs in pneumoperitoneum (Figure
38).121 This arcuate radiographic lucency projects across the midline caudal to the heart in the subxiphoid region.122
The cupola sign represents free intraperitoneal air located within the subphrenic space.123
The subphrenic space is located anterior to the stomach and the
gastrohepatic ligament. This space creates a well-defined superior
border to the gas collection, thus forming the cupola sign.
central tendon of the diaphragm forms the well-defined superior margin
of the cupola sign. The central tendon is composed of the right, left,
and central diaphragmatic leaves. Gas collects below the central leaf,
the most anterior portion of the diaphragmatic tendon, when the patient
Potential mimickers of the cupola sign
can occur with the presence of air within the lesser sac, gas within the
high transverse colon, gas within a horizontally-oriented stomach,
pneumopericardium, or pneumomediastinum.122
recognition of classic radiologic signs that resemble familiar
real-world objects can be helpful in diagnosis. These signs result
directly from the underlying pathophysiology associated with either a
single or a well-defined group of entities. Appreciation of these
“objects” in a background of more complex and potentially confusing
imaging findings will assist in reaching an accurate diagnosis or assist
in selection of additional studies to narrow the diagnostic
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