Approach to Chest X-Ray and Interpretation

JSS Medical College, Mysuru
Normal Chest X-Ray &
Approach to Chest X-Ray
Dr.Vikram Patil
Assistant Professor, Radiology
JSS Medical College and Hospital, Mysuru

Introduction
• Most of the chest x-rays you will see will be
normal
• In order to recognise abnormality, you need
to know what a normal CXR looks like

General Principles
• Have a systematic approach
• Interpret the CXR in conjunction with the
clinical findings
• Always compare with previous CXR if available
to assess for change
• Ask yourself “Does my interpretation make
sense?”

Before we start……
Relative Densities
The images seen on a chest radiograph result from the differences in
densities of the materials in the body.
The hierarchy of relative densities from least dense (Black) to most
dense (white) :
•Gas (air in the lungs)
•Fat (fat layer in soft tissue)
•Water (same density as heart and blood vessels)
•Bone (the most dense of the tissues)
•Metal (foreign bodies)

Before Interpreting the Radiograph …
1. Patient identification details
2. X-Ray view-PA, AP, Lateral….
3. Breath : Inspiration or Expiration
4. X-ray penetration : Under or Over penetrated
5. Rotation

Four major views of a chest
radiograph:
• Posterior-anterior (PA)
• Lateral
• Anterior-posterior (AP)
• Lateral Decubitus

Posterior-anterior (PA) Position
• The standard position for obtaining a routine adult chest
radiograph
• Patient stands upright with the anterior wall of chest placed
against the front of the film
• The shoulders are rotated forward enough to touch the film,
ensuring that the scapulae do not obscure a portion of the lung
fields
• Usually taken with the patient in full inspiration
• The PA film is viewed as if the patient is standing in front of you

Anterior-posterior (AP)
Position
• Used when the patient is debilitated, immobilized, or unable
to cooperate with the PA procedure
• Film is placed behind the patient’s back with the patient in a
supine position
• Heart is at a greater distance from the film hence appear
more magnified than in a PA
• The scapulae are usually visible in the lung fields because they
are not rotated out of the view as they are in a PA

PA view AP view
Scapula Seen in periphery of thorax Seen over lung fields
Clavicles Project over lung fields Above the apex of lung fields
Ribs Posterior ribs distinct Anterior ribs are distinct
Marker PA AP
View

Lateral Position
• Patient stands upright with the left side of the chest
against the film and the arms raised over the head
• Allows the viewer to see behind the heart and
diaphragmatic dome
• Typically used in conjunction with a PA view of the
same side of chest to help determine the three-
dimensional position of organs or abnormal densities

Lateral Decubitus Position
• The patient lies on either the right or left side rather than in
the standing position as with a regular lateral radiograph
• The radiograph is labeled according to the side that is placed
down (a left lateral decubitus radiograph would have the
patient’s left side down against the film)
• Often useful in revealing a pleural effusion that cannot be
easily observed in an upright view, since the effusion will
collect in the dependent position

Three Main Factors Determine the
Technical Quality of the
Radiograph
• Inspiration
• Penetration
• Rotation

Inspiration
The chest radiograph should be obtained with the
patient in full inspiration to help assess intrapulmonary
abnormalities.
At full inspiration, the diaphragm should be observed
at about the level of the 8th
to 10th
rib posteriorly, or the
5th
to 6th
rib anteriorly.

Inspiration Expiration
Good Inspiration:
•6 anterior ribs visible
•10 posterior ribs visible

Penetration
On a properly exposed chest radiograph:
•The lower thoracic vertebrae should be visible through
the heart
•The bronchovascular structures behind the heart
(trachea, aortic arch, pulmonary arteries, etc.) should
be seen

Underexposure
In an underexposed chest
radiograph, the cardiac shadow is
opaque, with little or no visibility of
the thoracic vertebrae.
The lungs may appear much denser
and whiter, gives appearance of
infiltrates.

Overexposure
With greater exposure of the chest
radiograph, the heart becomes more
radiolucent and the lungs become
proportionately darker.
Often gives the appearance of lacking
lung tissue, as would be seen in a
condition such as emphysema.

Penetration
Over-penetrated Under-penetrated
If intervertebral disc are very
clearly seen in the film
If intervertebral disc are not
seen in the film
Correct exposure : Barely able to see the intervertebral disc through the heart

Rotation
Patient rotation can be assessed by observing the clavicular
heads and determining whether they are equal distance from
the spinous processes of the thoracic vertebral bodies.

Rotation

Angulation:
• With the patient in a more lordotic projection the clavicles
will project superiorly relative to the upper thorax causing
some distortion of the normal mediastinal anatomy.
• With the lordotic projection, the ribs assume a more
horizontal orientation.
• Occasionally a lordotic x-ray can be obtained intentionally to
better visualize structures in the thoracic apex obscured by
overlying bony structures.

Angulation

•Name/Date..
•Marker
•Inspiration/
•Rotation/
•Penetration
Review of Basics……..
clavicles equidistant
from spinous processes
of thoracic spine
can just see lower
thoracic spine
AMESH
Y/M
01/11/2016
09:23

Approach
• In order to recognise abnormality, you need
to know what a normal CXR looks like
The CXR on the next slide is normal.
How would you interpret it?

21
Normal Radiograph

ABCDEFGHI approach
• Airway
• Bones and Soft tissue
• Cardia
• Diaphragm
• Effusions
• Fields(Lung fields)
• Gastric Bubble
• Hila and mediastinum
• Impression

A-Airway

B-Bones and Soft Tissues
•Look at each rib in turn
•Clavicles
•Scapulae and humeri if visible
•Lower cervical and thoracic spine

Soft Tissue
• Thick soft tissue due to obesity may obscure some underlying
structures such as lung markings
• Breast tissue may obscure the costophrenic angles
• Lucencies within soft tissue may represent gas (as observed with
subcutaneous air)

•Supraclavicular fossae
(enlarged nodes)
•Lateral chest wall
(surgical emphysema)
•Under diaphragm
(pneumoperitoneum)
Soft Tissues

Subcutaneous Emphysema Pneumoperitoneum

C-Cardia
• Two-thirds of the heart should lie on the left side of the chest, with
one-third on the right
• The heart should take up less that half of the thoracic cavity (C/T
ratio < 50%)
• The left atrium and the left ventricle create the left heart border
• The right heart border is created entirely by the right atrium (the
right ventricle lies anteriorly and, therefore, does not have a
border on the PA view)

C-Cardia

T
CR
CL
CT RATIO = CR + CL / T
CR + CL = TRANSVERSE CARDIAC DIAMETER
T = TRANSVERSE THORACIC DIAMETER (at max TC dia)
C-Cardia

Pneumomediastinum Pneumopericardium

Mach Effect
• Sometimes a normal CXR will show
a thin, well-defined, black line
around one or both lateral margins
of the heart.
• An optical illusion resulting from
overlap of superimposed normal
structures.
• This illusion is known as a Mach
band or Mach effect

D-Diaphragm
•Both diaphragms should form a sharp margin with the lateral chest wall
•Both diaphragm contours should be clearly visible medially to the spine

Diaphragmatic humps

E-Effusions(Pleura)
The pleura and pleural spaces will only be visible when there is an abnormality present
Common abnormalities seen with the pleura include pleural thickening, or fluid or air in the
pleural space.

Effusions ….
Meniscus sign +
Subpulmonic effusion
Hydropneumothorax
Phantom tumor

Pneumothorax

F-Lung Fields
• Normally, there are visible markings throughout the lungs due
to the pulmonary arteries and veins, continuing all the way to
the chest wall
• Both lungs should be scanned, starting at the apices and
working downward, comparing the left and right lung fields at
the same level

F-Lung Fields

Lungs
• On a PA radiograph, the minor fissure can often be seen as a
faint horizontal line dividing the RML from the RUL.
• The major fissures are not usually seen on a PA view because
they are being viewed obliquely.

Pulmonary Venous Hypertension
• Interstitial edema with Kerley B lines

Lobar anatomy

Lobar anatomy..

Hidden Areas….

G-Gastric Bubble

H-Hilum and mediastinum
• The hila consist primarily of the major bronchi and
the pulmonary veins and arteries
• The hila are not symmetrical, but contain the same
basic structures on each side
• The hila may be at the same level, but the left hilum
is commonly higher than the right
• Both hila should be of similar size and density

H-Hilum and mediastinum

Pulmonary Arterial Hypertension
Enlargement of the pulmonary trunk and main pulmonary arteries
Disproportionately small peripheral vessels
Oligemic lungs
Prune tree appearance

Mediastinum
• The trachea should be centrally located or slightly to the right
• The aortic arch is the first convexity on the left side of the
mediastinum
• The pulmonary artery is the next convexity on the left, and
the branches should be traceable as it fans out through the
lungs
• The lateral margin of the superior vena cava lies above the
right heart border

Mediastinum

ICU- Tubes & Lines
Tip at Junction of SVC &
Right atrium

•PROBLEM SOLVING TOOLS

PREVIOUS CXR
• Previous CXRs your best friend. You see a real or possible
abnormality on the CXR.
• Was it there before? Has it got larger or smaller? Is it
unchanged?
• A previous CXR will often highlight an important but subtle
change.
• On the other hand it will frequently provide reassurance that
all is well.

Silhouette Sign
• An intrathoracic lesion touching a border of the heart,
aorta, or diaphragm will obliterate part of that border
on the radiograph.

AIR BRONCHOGRAM SIGN
• When the internal tubular outline of a bronchus is visible
within a thoracic opacity…that is an air bronchogram.
• It is most commonly associated with a simple pneumonia.
Sometimes it occurs with pulmonary oedema.

THE CARDIAC DENSITY
• The density (opacity) of the cardiac shadow should be equal
on both sides of the spine.
• If there is any difference in density then look for evidence
of pneumonia, or lower lobe collapse, or a lower lobe mass
on the denser side
• There should be no abrupt change in density across the
cardiac shadow.

LUNG APICES
• Thickening of the apical pleura — sometimes referred to as
an apical cap — occurs normally in 10% of middle-aged and
elderly people.
• Unfortunately, a superior sulcus carcinoma (e.g. a Pancoast
tumour) can mimic an apical cap

PERIPHERAL OPACITIES
• An intrapulmonary opacity abutting the pleura forms
an acute angle at the interface.
• A pleural or extrapleural lesion forms an obtuse
angle

HILA ASSESSMENT
• The left hilum should be higher than the right. Occasionally the
hila are at the same level…but the right hilum should never be
higher than the left
• Most (unilateral) enlarged hila are both lumpy / bumpy and
denser than the opposite normal side. Some normal hila will
appear prominent — but are actually within the normal range.

HILUM CONVERGENCE SIGN
• Distinguishes enlarged hilum due to enlarged pulmonary
arteries to be distinguished from enlargement due to
tumour.
• If vessels arise from or converge directly onto the hilar
shadow — then the enlargement is vascular.
• If the vessels appear to arise or converge medial to the
lateral aspect of the hilar shadow — then the enlargement is
a mass

HILUM OVERLAY SIGN
• This sign is often misunderstood and misrepresented.
• Hilum lateral to the lateral border of the “mass” — cardiac
enlargement.
• Hilum medial to the lateral border of the “mass” —
mediastinal mass present.

DESCENDING PULMONARY ARTERIES
• Always look for and identify the lower lobe pulmonary arteries…
each will have a diameter similar to little finger.
• If either is missing, look for any other CXR features that suggest
collapse of a lower lobe.
• Right lower lobe pulmonary artery identified in approx 94% of
normal CXRs.
• Left descending pulmonary artery sometimes more difficult to
identify —visible in 62% of normal people

FOR RIBS
• If a rib abnormality is suspected on clinical grounds
(e.g. trauma) then before deciding that the ribs are
normal:
– Rotate the image through 90º and assess the ribs in this
second position.
– Then turn the original image through 180º (i.e. look at it
upside down) and evaluate the ribs in this third position

RIGHT PARATRACHEAL STRIPE APPEARANCE
• The wall of the right side of the trachea is visualised in approx 60% of
adult patients.
• The air within the trachea outlines its inside margin and the lung air
outlines its outside margin.
• In 40% of normal adults the lung does not abut the outside wall and so
this stripe (or line) will not be seen.
• When visible it should measure <2.5 mm in width .
• Stripe >2.5 mm –suspect adjacent lymph node enlargement

PARAVERTEBRAL STRIPE
• Left paravertebral stripe is visualised on most normal frontal CXRs.
• Extends from the level of the arch of the aorta to the diaphragm.
• It represents a deflection of the pleura posteriorly by the adjacent
descending thoracic aorta .
• Any focal bulge of the left paravertebral stripe-vertebral pathology
requires exclusion.
• A right paravertebral stripe is not visualised until middle age, when age
related marginal osteophytes can cause pleural displacement.
• A visualised right paravertebral stripe is always abnormal…unless age
related osteophyte formation is present.

THORACO-ABDOMINAL SIGN
• A sharply marginated mediastinal mass projected over the
diaphragm on a CXR (or on an AXR) will lie wholly or partly in
the thorax…because it is outlined by the air in the lung.
• If the lower lateral margin of the lesion does not converge,
and particularly if it diverges, then a significant amount of the
lesion lies within the abdomen (e.g. a paraspinal abscess).

CERVICO-THORACIC SIGN
• If the lateral outline of the mass is visualised above the
clavicle then the mass is situated posteriorly.
• If the lateral outline of the mass fades away as it reaches the
lower border of the clavicle then the mass is situated
anteriorly

Spine Sign -Posterior mediastinal mass

SUBCARINAL ANGLE
• Carina - site of the division of the trachea into the right and left
main bronchi.
• Normal angle varies from 50° to 100°.
• Angle greater than 100° implies the two main bronchi are
being pushed apart.
• Can be due to subcarinal tumour / lymph node enlargement or
to an enlarged left atrium (e.g. mitral valve stenosis).

Azygous Vein
• The azygos vein enters the superior vena cava to the right of the
tracheal bifurcation
• If the transverse diameter exceeds 1.0 cm
(a) determine whether the patient is in heart failure; and
(b) check whether the clinical presentation might include the possibility of
nodal enlargement.

UNILATERAL HYPERTRANSRADIANCY
• Detecting unilateral hypertransradiancy is subjective and
depends on how meticulously you look for it.
• Some observers are very sensitive to a difference between
the blackening of the two lungs.
• Frequently the cause is technical(Rotation).
• Other causes: Mastectomy, Sweyer James Syndrome, Poland
syndrome…

Pediatric points
• On an infant’s AP radiograph the normal cardiothoracic ratio
(CTR) should not exceed 60%.
• On a child’s PA radiograph the normal CTR can be slightly
above 50%, though by the second year it rarely exceeds 50%
• The thymic shadow is visible at birth, normally involutes
between the ages of two and eight years

Before we Conclude

Expiration vs Inspiration

Penetration…

Foreign Body…..

Soft Tissue-NF Lung-Mets
Nipple
shadow
SPN

Looks Normal????

Coarctation of aorta

Pectus Excavatum

Hiatus Hernia with gastric volvulus

Kartegeners Syndrome

Take home message
• Look carefully for patient identification details and technical issues
• Be systematic in approach
• It’s a chest X-ray, not a lung x-ray.
• Concentrate on hidden areas
• Compare with old films and lateral films

This presentation will be made
available on
www.jssmcradiology.com
Thank you

Approach to Chest X-Ray and Interpretation

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