AXR Made Easy
AXR Made Easy
AXR Made Easy
normal radiographs
Understanding x ray films is something that all clinical students
should get to grips with. Starting out as a doctor, you will not need
to be an expert but you will need to know the basics. Ian Bickle
and Barry Kelly present the first part of a new series on interpreting
plain abdominal radiographs
The abdominal radiograph is one of the
most commonly requested images, and all
medical students should have a knowledge
of common radiological interpretations.
This article covers the radiology of normal
findings. Subsequent parts of the series will
cover abnormal intraluminal gas, abnormal
extraluminal gas, calcification, bone and
soft tissue abnormalities, and iatrogenic,
accidental, and incidental objects.
The standard abdominal radiograph
(AXR) taken is a supine projection: x rays
are passed from front to back (anteroposterior projection) of a patient lying down on
his or her back. In some circumstances an
erect AXR is requested: its advantage over a
supine film is the visualisation of air-fluid levels. A decubitus film (patient lying on his or
her side) is also of use in certain situations.
Although an AXR is a plain radiograph, it
has a radiation dose equivalent to 50 posteroanterior chest x rays or six months of
standard background radiation.
As with any plain radiograph, only five
main densities are seen, four of which are
natural: black for gas, white for calcified
structures, grey representing a host of soft
tissue with a slightly darker grey for fat (as it
absorbs slightly fewer x rays). Metallic objects
are seen as an intense bright white. The clarity of outlines of structures depends, therefore, on the differences between these
densities. On the chest radiograph, this is
easily shown by the contrast between lung
and ribsblack air against the white calcium
containing bones. These differences are
much less apparent on the AXR as most
structures are of similar densitymainly soft
tissue.
Intraluminal gas
Begin by looking at the amount and distribution of gas in the bowels (intraluminal
gas). There is considerable normal variation
in distribution of bowel gas. On the erect
Technical features
It is important, as with any image, that the
technical details of an AXR are assessed.
The date the film was taken and the name,
age, and sex of the patient are all worth noting. This ensures you are interpreting the
correct film with the correct clinical information and it also may aid your interpretation. You would be a little concerned if you
saw what appeared to be a calcified fibroid
on an AXR when holding the notes of Mr
John Brown.
Next ask what type of AXR is it: supine,
102
greater, but if it is greater than 9 cm it is abnormal. Large bowel should lie at the periphery
of the film, with small bowel distributed centrally. Small and large bowel can also be distinguished, most easily when dilated, by their
different mucosal markings. Small bowel has
valvulae conniventes that transverse the full
width of the bowel; large bowel has haustra
that cross only part of the bowel wall (figs 3
and 4). These features are important in the
next part of this series, which considers abnormal intraluminal gas. Occasionally, fluid levels
in the small bowel are a normal finding.Valvulae conniventes and haustra films
Faecal matter in the bowel gives a mottled appearance (fig 5). This is seen as a
mixture of grey densities representing a gasliquid-solid mixture.
Extraluminal gas
AXR, the gastric gas bubble in the left
upper quadrant of the film is a normal finding. Gas is also normally seen within the
April 2002
studentbmj.com
Calcification
Calcium is visible in a variety of structures,
both normal and abnormal, and becomes
more common with advancing age. However, review the following areas in particular for evidence of calcification: cartilage of
ribs, blood vessels (chiefly the aortoiliac and
splanchnic arteries), pancreas, kidneys, the
right upper abdominal quadrant for gallbladder calculi, and the pelvis, which may
contain a variety of calcified structures,
STUDENT BMJ VOLUME 10
April 2002
Artefacts
most commonly phleboliths. Part 4 of this
series is dedicated to calcification on AXR.
studentbmj.com
Review points
Technical specifics of the radiograph
Amount and distribution of gas
Extraluminal gas
Calcification
Soft tissue outlines and bony struc-
tures
Iatrogenic, accidental, and incidental
objects
103
Volvulus
A volvulus is the twisting of bowel about its
mesentery, causing intestinal obstruction.
The two most common sites are the sigmoid
and the caecum. With a sigmoid volvulus, an
extremely dilated loop of sigmoid bowel
forms two large compartments which look
like a coffee bean (hence the name of the
sign). This single loop usually fills most of the
lower abdominal radiograph. On erect
abdominal radiographs a fluid level may be
noted.
Comparison of large and small bowel
obstruction features
Feature
Obstruction
Small
Large
bowel
bowel
>5
Central
Peripheral
Many
Few
Many, short
Few, long
Valvaulae
Haustra
No
May 2002
Yes
studentbmj.com
Bickle IC, Kelly B. Abdominal x rays made easy: normal radiographs. studentBMJ 2002;10:102-3. (April.)
May 2002
studentbmj.com
Fig 6. Meteorism
141
Pneumoperitoneum
A most important and potentially devastating finding is that of free intraperitoneal
gas, which is known as pneumoperitoneum.
Emergency surgical intervention is likely to
be necessary, as pneumoperitoneum usually indicates a perforated viscus. The supplementary plain radiograph should be an
Riglers sign
Falciform
ligament
Fig 1. Gross pneumoperitoneum with free air under both hemidiaphragms. In addition
there is a large dark egg shape projected through the heart. This is a large, fixed, hiatus
herniaan incidental finding, but one which shows an abnormal air collection
180
JUNE 2002
studentbmj.com
Miscellaneous causes
Chilaiditis syndrome
Chilaiditis syndrome is an important normal variant on the erect chest radiograph,
which must be distinguished from pathological free gas under the diaphragm. In
this phenomenon, gas is seen between the
hemidiaphragm and the liver or spleen (fig
4). On close and careful observation this
should be identified as gas filled large
bowel, most likely transverse colon (apparent, as haustra are seen within the gas filled
structure). This gas is still contained in the
bowel loop.
Subphrenic abscess
This is a localised collection of free gas and
fluid, which usually forms under the right
hemidiaphragm, above the solid liver. This
gas collection usually occurs above the 11th
rib (fig 5).
Biliary gas
On the plain abdominal x ray film, gas is
not normally identified in the biliary sysSTUDENT BMJ VOLUME 10
JUNE 2002
studentbmj.com
181
Calcification of normal
structures (box 1)
Evaluation of the abdominal radiograph
might start at the top, working down the
film. The film should include the lower
anterior ribs. As you will recall, towards
the midline anteriorly, a rib changes from
bone to cartilage and is termed costal cartilage. The cartilage of ribs one to seven
articulates with the sternum whereas ribs
eight to 10 indirectly connect to the sternum by three costal cartilages, each of
which is connected to the one immediately adjacent to it (ribs 11 and 12 are
floating). This cartilage can calcify, which
is termed costocalcinosis. Although
appearing strikingly abnormal, it is harmless and usually age related (fig 1).
Further down, mesenteric lymph nodes
may calcify and appear as oval, smooth,
outlined structures (fig 2). These can be
confused with small kidney stones, especially in a patient without previous films
who presents with abdominal pain. Are
such incidental harmless calcified nodes
272
Fig 2
Fig 1
Fig 3
Calcium is pathology
Biliary calculi
Renal calculi
Appendicolith
Bladder calculi
Teratoma
Calcification indicating
pathology (box 2)
Renal calcification
Pancreas
The pancreas lies at the level of T9-T12
vertebrae. Calcification of the pancreas is
usually found in chronic pancreatitis,
although there are some rarer causes. If
calcification is extensive, the full outline of
the pancreas may be observed, mostly on
the left side, but may cross over the midline. This speckled calcification occurs
on the network of ducts within the pancreatic tissue where most of the calcium is
deposited (fig 3).
Vascular calcification
Perhaps the most striking calcification is in
the blood vessels, most notably the arteries. The whole vessel(s) may be exquisitely
AUGUST 2002
studentbmj.com
Fig 4
Fig 5
Gynaecological calcification
The final structure in this section is found
only in womenfibroids. These can
become calcified and appear as rounded
structures of varying size and location in
the pelvis (fig 6).
Pathological calcification
The final section on calcification on
abdominal x ray film refers to pathological calcification. This almost exclusively
manifests as calculi in various locations.
Calculi may be asymptomatic.
Biliary calculi
Biliary calculi are commonly referred to
as gallstones. Plain abdominal x ray film
in itself is poor at identifying these calculi
and detects only 10-20%. Ultrasound is
the gold standard for first line imaging. A
plain abdominal radiograph is often the
initial investigation in patients with
abdominal pain and may identify these
STUDENT BMJ VOLUME 10
AUGUST 2002
Fig 6
studentbmj.com
273
Renal calculi
These are much more commonly identified on the abdominal radiograph; up to
80% are visible. The variable detection is a
Fig 8
Fig 7
Fig 9
Neurodegenerative terms
-Amyloid: -Amyloid protein causes problems only when it is converted from its normal soluble form to insoluble -pleated sheets,
which accumulate into neurotoxic amyloid plaques. In its healthy
role it is probably involved in stabilising cell walls.
Prions: These are proteins produced by the prion gene and probably have a role in maintaining the electrical activity of cells. In
Creutzfeldt-Jakob disease, the normal soluble form changes its
configuration by folding up differently, allowing it to form insoluble -pleated sheet structures. The protein forms prion plaques
that are neurotoxic. The pathological changes are transmissible.
-Synuclein: This protein is found in Parkinsons disease and
dementia with Lewy bodies. Its role in the normal state is unclear.
In pathological states this protein forms intraneuronal inclusions
(Lewy bodies).
Tau: This protein is found in the microtubules of nerve cells, and
its role is to help stabilise them. The role of microtubules is to
transport cellular components. In Alzheimers disease, tau protein
becomes hyperphosphorylated and then accumulates into neurofibrillary tangles that disrupt the microtubules. In frontal lobe
dementias the balance of different forms of tau protein change,
interfering with transportation in the cells.
274
AUGUST 2002
studentbmj.com
intraluminal gas
Extraluminal gas
Bones
Calcification
Bone and soft tissues
Iatrogenic,
objects
Anatomy
Bones include the lower ribs and their articulations, the lower thoracic and the lumbar
spine, the bony pelvis, and the proximal
femora. Soft tissues include the abdominal
viscera and the surrounding muscle and
soft tissues that envelop the lower trunk.
Pathology of the bone and soft tissues can
be identified on abdominal x ray film for
three main reasons: it may be new pathology, causing the symptoms that precipitated
the abdominal x ray film, associated pathology, or concomitant pathology.
Pagets disease
Osteophyte formation
Osteoarthritis
Subchondral sclerosis
Fractures
Fig 1: Scoliosis and kyphosis
Ankylosing spondylitis
STUDENT BMJ VOLUME 10
SEPTEMBER 2002
studentbmj.com
Bone cysts
315
Soft tissues
The yield of positive radiographic findings
involving the soft tissues is less than for
bone. Calcification involving soft tissue
structures was discussed in an earlier part
of this series.1 Alteration in size and shape
of solid organs, such as the kidneys (box
4), liver, and spleen can be observed, as
may the loss of their properitoneal fat
lines. Furthermore, the loss of the psoas
muscle shadows may indicate intraperitoneal disease (see Fig 4)
SEPTEMBER 2002
studentbmj.com
as a tube device, most commonly the nasogastric tube (figure 1). These are the most
commonly found iatrogenic objects, and
their position is sometimes confirmed by a
chest x ray film.
Other devices may be in the vascular,
hepatopancreatobiliary, gastrointestinal, and
Internal objects
Iatrogenic
Biliary or vascular stent
intrauterine coil devices
Sterilisation clips
Surgical clips
Greenfield filter (inside inferior vena
cava)
Percutaneous endoscopic gastrostomy
tube
Nasogastric tube
Accidental
Swallowed objects: razor blades,
OCTOBER 2002
Iatrogenic objects
External objects
Incidental
studentbmj.com
Stoma ring
Objects in clothing: coins, keys, comb
Objects on clothing: buttons, clips,
zips
369
Incidental objects
Accidental objects
genitourinary systems.
Evidence of vascular intervention may be
370
OCTOBER 2002
studentbmj.com