Abdominal X-ray Radiological Signs
Suzanne O’Hagan
Lightbulb moment
a moment of sudden inspiration, revelation, or recognition
Approach to AXR
• Bowel gas pattern
• Extraluminal air
• Soft tissue masses
• Calcifications
Normal AXR
Liver
11th rib
T12
Gas in
stomach
Splenic flexure
Psoas margin
Left kidney
Hepatic flexure
Transverse colon
Iliac crest
Gas in sigmoid
Sacrum
Gas in
caecum
SI joint
Bladder
Femoral head
Gas pattern
What is normal?
• Stomach
– Almost always air in stomach
• Small bowel
– Usually small amount of air in
2 or 3 loops
• Large bowel
– Almost always air in rectum
and sigmoid
– Varying amount of gas in rest of large bowel
Normal fluid levels
• Stomach
– Always (upright, decub)
• Small bowel
– Two or three levels
acceptable (upright, decub)
• Large bowel
– None normally
(functions to remove fluid)
Large vs small bowel
• Large bowel
– Peripheral (except RUQ occupied by liver)
– Haustral markings don’t extend from wall to wall
• Small bowel
– Central
– Valvulae conniventes extend across lumen and are
spaced closer together
Radiographic principles
Series of films for acute abdomen
• Obstruction series/ Acute abdominal series/
Complete abdominal series
– Supine (almost always)
– Upright or left decubitus (almost always)
– Prone or lateral rectum (variable)
– Chest, upright or supine (variable)
Acute abdominal series
What to look for
VIEW
LOOK FOR
SUPINE ABDOMEN
Bowel gas pattern
Calcifications
Masses
PRONE ABDOMEN
Gas in rectosigmoid
Gas in ascending and
descending colon
UPRIGHT ABDOMEN
Free air, air-fluid levels
UPRIGHT CHEST
Free air, lung pathology
secondary to intraabdominal
process
Substitutes:
Prone
Lateral rectum
Upright
Left lateral decub
Upright chest
Supine chest
Obtaining views
•
Supine
– Patient on back, x ray beam directed
vertically downward, casette
posterior, x-ray tube anterior (AP)
•
Prone
– Patient on abdomen, x-ray beam
directed vertically downward, cassette
anterior, x-ray tube posterior (PA)
•
Upright
– Patient stands or sits, x-ray beam
directed horizontally, cassette
posterior, x-ray tube anterior (AP)
•
Upright chest
– Patient stands or sits, horizontal x-ray
beam, cassette anterior, x-ray tube
posterior (PA)
1900s X-Ray-based fluoroscopy machine
in which radiation is shot directly through
the patient and into the doctor’s face.
Abnormal Gas Patterns
• Functional ileus
– One or more bowel loops become aperistaltic usually
due to local irritation or inflammation
• Localised “sentinel loops” (one or two loops)
• Generalised (all loops of large and small bowel)
• Mechanical obstruction
– Intraluminal or extraluminal
• Small bowel obstruction
• Large bowel obstruction
3, 6, 9
RULE
Maximum Normal Diameter of bowel
Small bowel
3cm
Large bowel
6cm
Caecum
9cm
Localised ileus
Key features
• One or two persistently dilated
loops of small or large bowel
(multiple views)
• Often air-fluid levels in sentinel
loops
• Local irritation, ileus in same
anatomical region as pathology
• Gas in rectum or sigmoid
• May resemble early SBO
Causes of Localised Ileus
by location
SITE OF DILATED LOOPS
CAUSE
Right upper quadrant
Left upper quadrant
Right lower quadrant
Left lower quadrant
Cholecystitis
Pancreatitis
Appendicitis
Diverticulitis
Mid-abdomen
Ulcer or kidney/ureteric calculi
Colon cut off sign
Abrupt cutoff of colonic gas column at the splenic flexure (arrow). The colon is
usually decompressed beyond this point.
Explanation:
Inflammatory exudate in acute
pancreatitis extends into the
phrenicocolic ligament via lateral
attachment of the transverse
mesocolon
Infiltration of the phrenicocolic
ligament results in functional
spasm and/or mechanical
narrowing of the splenic flexure at
the level where the colon returns
to the retroperitoneum.
Generalised ileus
Key features
• Entire bowel aperistaltic/hypoperistaltic
• Dilated small bowel and large bowel to rectum
(with LBO no gas in rectum/sigmoid)
• Long air-fluid levels
CAUSE
REMARK
*Postoperative
Usually abdominal surgery
Electrolyte imbalance
Diabetic ketoacidosis
* almost always
Generalised adynamic ileus
The large and
small bowel are
extensively airfilled
but not dilated.
The large and
small bowel "look
the same".
Mechanical SBO
• Dilated small bowel
• Fighting loops (visible loops, lying transversely,
with air-fluid levels at different levels)
• Little gas in colon, especially rectum
SBO Erect
Air fluid levels
SBO Supine
Causes of Mechanical SBO
Adhesions
Hernia*
Malignancy
Gallstone ileus*
Intussesception
Inflammatory bowel disease
* May be visible on AXR
Step ladder appearance
• Loops arrange
themselves from
left upper to
right lower
quadrant in
distal SBO
Coil spring sign
String of pearls sign
Considered diagnostic of obstruction (as opposed to ileus)
and is caused by small bubbles of air trapped in the
valvulae of the small bowel.
Stretch/slit sign
Slit of air caught in a
valvulae, characteristic
of SBO
Closed loop obstruction
• Two points of same loop of bowel obstructed
at a single location
• Forms a C or a U shape
– Term applies to small bowel, usually caused by
adhesions
– Large bowel, called a volvulus
Crescent Sign
Caused by:
LUQ Soft tissue mass
OR
Head of intussusception
in distal transverse colon
Double Bubble Sign
Duodenal Atresia
Mechanical LBO
• Colon dilates from point
of obstruction
backwards
• Little/no air fluid levels
(colon reabsorbs water)
• Little or no air in
rectum/sigmoid
Large bowel obstruction
Bowel loops tend not to
overlap therefore
possible to identify site
of obstruction
Little or no gas in small
bowel if ileocaecal valve
remains competent*
* If incompetent, large bowel
decompresses into small bowel, may
look like SBO
Causes of Mechanical LBO
TUMOUR
VOLVULUS
HERNIA
DIVERTICULITIS
INTUSSUSCEPTION
Note on volvulus
• Sigmoid colon has its own mesentry therefore
prone to twisting
• Caecum usually retroperitoneal and not prone
to twisting; 20% people have defect in
peritoneum that covers the caecum resulting
in a mobile caecum
Volvulus
A volvulus always extends away from the area of
twist. Sigmoid volvulus can only move upwards and usually
goes to the right upper quadrant. Caecal volvulus
can go almost anywhere.
Coffee Bean Sign
Sigmoid volvulus
Massively
dilated
sigmoid loop
Hernia
Lateral decubitus of value
The advantage is that there may be a greater chance of air entering the
herniated bowel because it is the least dependent part of the bowel in the
supine position.
Apple core sign
• Radiologic manifestation of a
focal stricture of the bowel
usually at contrast material
enema examination. The
stricture demonstrates
shouldered margins and
resembles the core of an
apple that has been partially
eaten. The most common
cause is an annular carcinoma
of the colon.
Thumbprinting
The distance between
loops of bowel is increased
due to thickening of the
bowel wall.
The haustral folds are very
thick, leading to a sign
known as 'thumbprinting.'
Lead pipe
colon
• Shortening of
colon secondary
to fibrosis
• Loss of
haustration
• Ulcerative colitis
Extraluminal air
• TYPES
– Pneumoperitoneum/free air/intraperitoneal air
– Retroperintoneal air
– Air in the bowel wall (pneumatosis intestinalis)
– Air in the biliary system (pneumobilia)
Upright film best
• The patient should be positioned sitting
upright for 10-20 minutes prior to acquiring
the erect chest X-ray image.
• This allows any free intra-abdominal gas to
rise up, forming a crescent beneath the
diaphragm. It is said that as little as 1ml of gas
can be detected in this way.
Free Air
Causes
• Rupture of a hollow viscus
–
–
–
–
Perforated peptic ulcer
Trauma
Perforated diverticulitis (usually seals off)
Perforated carcinoma
• Post-op 5-7 days normal, should get less with successive
studies *NOT ruptured appendix (seals off)
Signs of free air
•
•
•
•
•
•
•
•
Crescent sign
Chilaiditis sign
Riglers (and False Rigler’s)
Football sign
Falciform ligament sign
Triangle sign
Cupola sign
Lesser sac sign
Crescent Sign II
Free air under the diaphragm
Best demonstrated on
upright chest x rays or
left lat decub
Easier to see under
right diaphragm
Chilaiditis sign
• May mimic air under
the diaphragm
• Look for haustral folds
• Get left lat decub to
confirm
In patients who have cirrhosis
or flattened diaphragms due to
lung hyperinflation, a void is
created within the upper
abdomen above the liver. This
space may be filled by bowel. If
this bowel is air filled then it
may mimic free gas.
Rigler’s Sign
Bowel wall visualised on both sides due to intra and extraluminal air
Usually large amounts of free air
May be confused with overlapping loops of bowel, confirm with upright view
False Rigler’s Sign
• The Rigler sign can sometimes be simulated by
contiguous loops of bowel, whereby
intraluminal air in one loop of bowel may
appear to outline the wall of an adjacent loop,
which results in a misdiagnosis of free air.
• Measure distance of interface if unsure
Football SIgn
Seen with massive
pneumoperitoneum
Most often in children
with necrotising
enterocolitis
In supine position
air collects anterior
to abdominal
viscera
Paediatric
Adult
Falciform ligament sign
Normally
invisible.
Supine film, free
air rises over
anterior surface
of liver
Other patterns of air around liver
Doge’s Cap Sign
Inverted V sign
• On the supine radiograph, an inverted "V"
may be seen over the pelvis in a patient with
pneumoperitoneum.
• While in infants this is produced by the
umbilical arteries, in adults it appears to be
created by the inferior epigastric vessels
Continuous diaphragm sign
Sufficient
free air, left
and right
hemidiaphragms
appear
continous
Lesser sac Sign
Cupola Sign
Cupola
sign
Lesser sac
sign
– (black
arrows)
The lesser sac is
positioned
posterior to the
stomach and is
usually a potential
space. There is
free connection
between the lesser
sac and the
greater sac
through the
foramen of
Winslow
– (white
arrows)
Air superior to
left lobe of liver
Double Bubble Sign
Cupola Sign
Air beneath the central tendon of the diaphragm
The term cupola comes from a dome such as
this famous dome of the Duomo in Florence.
Triangle Sign
• The triangle sign
refers to small
triangles of free gas
that can typically be
positioned between
the large bowel and
the flank
Retroperitoneal Air
• Recognised by:
– Streaky, linear appearance outlining
retroperitoneal structures
– Mottled, blotchy appearance
– Relatively fixed position
• May outline:
– Psoas muscles
– Kidneys, ureters, bladder
– Aorta or IVC
– Subphrenic spaces
Causes of retroperitoneal air
•
•
•
•
•
Bowel perforation (appendix, ileum, colon)
Trauma (blunt or penetrating)
Iatrogenic
Foreign body
Gas producing infection
Pneumoretroperitoneum
•
This patient has free air in
the retroperitoneal space.
The air is seen surrounding
the lateral border of the right
kidney (white arrow). There is
other evidence of free gas
including Rigler's sign.
•
If you are not confident that
the appearance is
pneumoretroperitoneum,
you can try an erect and
decubitus view to see if the
gas moves. If the gas is seen
to move, it's not in the
retroperitoneum.
Air in the bowel wall
• Signs
– Best seen in profile producing a linear lucency that
parallels the bowel
– Air en face has a mottled appearance resembling
gas mixed with faeculent material
Causes of air in bowel wall
• Primary Pneumatosis cystoides intestinalis (rare)
– usually affects left colon
– Produces cyst-like collections of air in the submucosa or serosa
• Secondary
– Diseases with bowel wall necrosis
– Obstructing lesions of the bowel that raise intraluminal pressure
• Complications
– Rupture into peritoneal cavity
– Dissection of air into portal venous system
Pneumatosis intestinalis
• Intramural air,
best
appreciated in
profile
Air in the biliary tree
• One or two tube-like branching lucencies in
the RUQ, conform to location of major bile
ducts
Causes
• “Normal” if Sphincter of Oddi incompetence
• Previous surgery including sphincterotomy or
transplantation of CBD
• Pathology (uncommon)
– Gallstone ileus: gallstone erodes through wall of
GB into the duodenum producing a fistula
between the bowel and the biliary system.
– Stone impacts in small bowel = mechanical SBO.
“ileus” misnomer
Biliary vs Portal Venous Air
• Portal venous air
usually associated
with bowel necrosis
• Air is peripheral
rather than central
• Numerous
branching
structures
Soft tissue masses
• Organomegaly
– Know normal landmarks
2 ways to identify soft tissue masses/organs:
– Direct visualisation of edges of structure
– Indirect by displacement of bowel
CT, US and MRI have essentially replaced conventional
radiography in the assessment of organomegaly and soft
tissue masses
Abdominal Calcifications
Location
Pattern
First exclude artefact
Kim Kardashian’s butt – real or artefact?
Location
•
•
•
•
•
•
•
•
•
•
•
Vascular
Liver
Gallbladder
Spleen
Pancreas
Lymph nodes
Adrenals
Kidneys
Ureters
Bladder
Prostate
Rim-like
• Calcification that has occurred in the wall of a
hollow viscus
– Cysts
• renal, splenic, hepatic
– Aneurysms
• aortic, splenic, renal artery
– Saccular organs
• Gallbladder
• Urinary bladder
Calcified hydatid cysts
Linear/Track
• Calcification in walls of tubular structures
Aortoiliac calcification
– Arteries
– Fallopian tubes
– Vas deferens
– Ureter
Chinese Dragon Sign
Calcified splenic artery
Calcified vas deferens
Floccular, Amorphous, Popcorn
• Formed in solid organ or tumour
– Pancreas (chronic pancreatitis)
– Leiomyomas of uterus
– Ovarian cystadenomas
– Lymph nodes
– Adenocarcinomas of stomach, ovary, colon
– Metastases
– Soft tissue (previous trauma, crystal deposition)
Calcified enteric
lymph nodes
Calcified fibroids
Calcified pancreas
Floccular
Lamellar or laminar
• Formed around a nidus inside hollow lumen
• Concentric layers due to prolonged movement
of stone inside hollow viscus
– Renal stones
– Gallstones
– Bladder stones
Bladder calculi
Lamellar
Renal calculi
Pelvicalyceal calcifications
Staghorn Calcification
Tubular
Renal stones are often small, but if large
can fill the renal pelvis or a calyx, taking on
its shape which is likened to a staghorn.
Renal calculi
Parenchymal calcification
Nephrocalcinosis
Uncommonly the renal
parenchyma can become
calcified.
This is known as
nephrocalcinosis, a condition
found in disease entities such
as medullary sponge kidney
or hyperparathyroidism.
Flocculent
Putty Kidney
• "Putty kidney" –
sacs of casseous,
necrotic material
(TB)
• Autonephrectomy
– small, shrunken
kidney with
dystrophic
calcification
Flocculent
Calcified gallstones
Lamellar
Conclusion
• Approach to AXR should include gas pattern,
extraluminal air, soft tissue and calcifications
• Named radiological signs are a useful way of
remembering, identifying and reporting on
films
References
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