How to read a chest X-ray

How to read a chest X-ray

Reading a chest X-ray requires a methodical approach that can be appliedto all films so that abnormalities are not overlooked.

Clinicians and
radiologists develop an individual approach but there are certain core areas
that should be looked at on all films.

These may be inspected in any order –
this is largely down to personal preference.

Listed below is the outline of a
method which can be applied to read chest X-rays.

Initial quick review of film
To identify any obvious abnormality.

Systematic analysis
Label
Verify the patient’s identity. In examination situations look at the name,
if present, as this can give a clue to sex and ethnic background.
The date and hospital where the film was taken give further clues. If a film
has been taken at a centre for oncology or chest medicine, for instance,
this may help with interpretation.

Projection and patient position
Postero-anterior (PA) is the preferred projection as this does not produce
as much radiographic magnification of the heart and mediastinum as
an antero-posterior (AP) projection. A PA film is taken with the film
cassette in front of the patient and the beam delivered from behind
with the patient in an upright position. Portable films and those taken on
intensive care are all AP projection. Patient position causes important
although sometimes subtle variations in appearance. The supine position
causes distension of the upper lobe blood vessels which may be confused
with elevated left atrial pressure. Imaging of a pleural effusion in a
supine position appears as faint increased density over a hemithorax – this
is due to fluid collecting in the dependent part of the chest, i.e. as a thin
layer posteriorly.
All films taken in the AP projection are usually labelled as such but to
avoid difficulties when describing films in examinations the use of the term
frontal projection is often helpful.
A lateral radiograph is used to localise lesions in the AP dimension;
locate lesions behind the left side of the heart or in the posterior recesses
of the lungs. A left lateral (with the left side of the chest against the film
and the beam projected from the right) is the standard projection.
The heart is magnified less with a left lateral as it is closer to the film.
To visualise lesions in the left thorax obtain a left lateral film and for
right-sided lesions a right lateral.
Lordotic views are taken to examine the lung apices if potential lesions
are partially obscured by overlying ribs or the clavicles. This view was
formerly taken in an AP position with the patient leaning backwards by
30 degrees. Now they are obtained in a PA position with the beam angled
downward by 45 degrees – a less awkward position for patients.
Expiratory films are used to assess air trapping in bronchial obstruction
such as a foreign body. A pneumothorax always appears larger on
an expiratory film and occasionally a small pneumothorax may only be
visible on expiration

Side marker

Dextrocardia is easily missed if the side marker is not identified.

Quality of film

Penetration – the vertebral bodies should just be visible through the
cardiac silhouette.

Rotation – the medial aspect of the clavicles should be symmetrically
positioned on either side of the spine.

Inspiration – the diaphragm should lie at the level of the sixth or seventh
rib anteriorly.
Large airways, lungs and pleura
The ‘lung shadows’ are composed of the pulmonary arteries and veins.
Apart from the pulmonary vessels, the lungs should appear black because
they contain air. Examine the lungs for density variation. Compare the
interspaces on the right with those on the left. Compare the right side with
the left just as you would, if auscultating the chest. Look all the way out
to the periphery of the lungs. Look at the overall lung vascularity and
compare one side with the other. It is important to look at the main
airways – the trachea and the main bronchi. Check the position of the
trachea, that it is central and not deviated.
Look at the pleural surfaces and the fissures, if visible. Check for
masses, calcifications fluid or pneumothorax.

Heart and mediastinum
Examine the cardiac outline identifying all the heart borders and the
outline of the great vessels (see Figs 1.1 and 1.2). Check that there are not
any abnormal densities projected through the cardiac silhouette. Look at
the aortic and pulmonary artery outlines. The heart and mediastinal outline
are made up of a series of ‘bumps’ (see Fig. 1.3). On the right side, there
are right braciocephalic vessels, the ascending aorta and superior vena cava,
the right atrium, and the inferior vena cava. On the left side, there are four
‘moguls’ in addition to the left brachiocephalic vessels: these are the aortic
arch, the pulmonary trunk, the left atrial appendage and the left ventricle.
The size and shape of each of these structures need to be looked at for
signs of enlargement or reduction in size. The right heart border is created
by the right atrium alone (the right ventricle is an anterior structure,
therefore does not contribute to any heart borders) – this is a question
examiners love to ask

Heart size can be estimated using the cardiothoracic ratio. The cardiac
measurement is taken as the greatest transverse heart diameter and is
compared to the greatest internal width of the thorax. A ratio of greater
than 0.5 is often used in clinical practice to indicate cardiomegaly.

Look at the position of the hila and their density – compare the
left with the right side. Tumours and enlarged lymph nodes can occur
here making the hila appear bulky.

Diaphragm

Check the shape, position and clarity/sharpness of both hemidiaphragms.
Both costophrenic angles should be clear and sharp. The cardiophrenic
angles should be fairly clear – cardiophrenic fat pads can cause added
density. The right hemidiaphragm is usually slightly higher than the left –
up to 1.5 cm. On the lateral film, the right hemidiaphragm is seen in its
entirety but the anterior aspect of the left hemidiaphragm merges with the
heart, so is not seen (see Fig. 1.6).

Bones

This is an area which is frequently overlooked.

Ribs: The ribs are a common site for fracture or metastatic deposits
but the remainder of the skeleton must also be carefully examined.
Identify the first rib and carefully trace its contour from the spine to its
junction with the manubrium. Each rib must be carefully and
individually traced in this manner, initially for one hemithorax and
then the contralateral side. A useful trick is to turn the film on its side,
rib fractures may then appear more obvious.

Thoracic spine: Look at the thoracic spine alignment – is it straight or
is there a scoliosis? Take particular care to exclude pathology from the
thoracic spine in trauma patients when even moderate malalignment can
be overlooked when projected through the heart or mediastinal shadows.

Clavicles scapulae and humeri: Fractures and dislocation of the humerus
are often obvious when looked for. Look for fractures, metastatic deposits,
abnormal calcifications or evidence of arthritis around the shoulders.

Soft tissues

A visual examination should be routinely performed on the chest wall,
the neck and both the breast shadows. Look for surgical emphysema and
abnormal calcification. With reference to the breast shadows be sure to
check whether there are two breast shadows and whether there is
symmetry of size, shape and position. The lung field missing a breast will
appear a little darker than the other side.

Review areas

These review areas are sites where pathology is commonly missed and
warrant a second look before any chest X-ray is reported as normal:

Breasts (symmetry/mastectomy).

Below the diaphragm, do not forget that the lungs extend below
the diaphragms, also look at the upper abdomen for surgical clips/
calcification/pneumoperitoneum.
Imaging the chest

Behind the heart (hiatus hernia/lung nodules/left lower lobe
collapse).

Thoracic spine and paraspinal lines (trauma).

Clavicle (nodule behind medial end and eroded lateral end).

Shoulder (dislocation).

Apices (pancoast tumour).

Hila (assess position, size and density).

Lung parenchyma.

Bones, especially ribs (look for metastases or fractures