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Chest x rays made easy
In the second of a five part series, Elizabeth Dick begins to look at chest abnormalities, starting with the mediastinum and heart
Fig 1 Normal chest x ray film |
The basics of looking at a chest x ray (recap):
- First look at the mediastinal contours - run your eye down the left side of the patient and then up the right.
- The trachea should be central. The aortic arch is the first structure on the left, followed by the left pulmonary artery; notice how you can trace the pulmonary artery branches fanning out through the lung (see figure 1).
- Two thirds of the heart lies on the left side of the chest, with one third on the right. The heart should take up no more than half of the thoracic cavity. The left border of the heart is made up by the left atrium and left ventricle.
- The right border is made up by the right
atrium alone. Above the right heart border
lies the edge of the superior vena cava.
- The pulmonary arteries and main bronchi
arise at the left and right hila. Enlarged
lymph nodes can also occur here, as can
primary tumours. These make the hilum
seem bulky - note the normal size of the
hila on this film.
- Now look at the lungs. Apart from the
pulmonary vessels (arteries and veins),
they should be black (because they are full
of air). Scan both lungs, starting at the
apices and working down, comparing left
with right at the same level, just as you
would when listening to the chest with
your stethoscope. The lungs extend behind
the heart, so look here too. Force your eye
to look at the periphery of the lungs - you
should not see many lung markings here;
if you do then there may be disease of the
air spaces or interstitium. Don't forget to
look for a pneumothorax.
- Make sure you can see the surface of the
hemidiaphragms curving downwards, and
that the costophrenic and cardiophrenic
angles are not blunted - suggesting an
effusion. Check there is no free air under
the hemidiaphragm.
- Finally, look at the soft tissues and bones.
Are both breast shadows present? Is there
a rib fracture? This would make you look
even harder for a pneumothorax. Are the
bones destroyed or sclerotic?
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| Presenting the film
You can summarise your findings in a few sentences: "The trachea is central, the mediastinum is not displaced. The mediastinal contours and hila seem normal. The lungs seem clear, with no pneumothorax. There is no free air under the diaphragm. The bones and soft tissues seem normal."
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The trachea and mediastinum are deviated
The trachea can be pulled or pushed,
almost always by one of three processes
(two that push, one that pulls). A right
sided pleural effusion will push the trachea and mediastinum to the left (fig 2).
Similarly, a left sided tension pneumothorax will push the mediastinum to
the right, as air builds up in the left
pleural space and cannot be released (fig 3).
On the other hand, if there is collapse
on the left this will pull the trachea and
mediastinum to the left side (fig 4). Most
other processes (consolidation, nontension pneumothorax, etc) have little
effect on the mediastinum. If you see the
mediastinum is shifted then you need to
think of these three things and look for
them (see future article).
An enlarged heart
The most common reason for the heart to
be enlarged is congestive cardiac failure,
so look for signs of left ventricular failure
on the rest of the film (fig 5). These are:
- Upper lobe blood diversion. The pulmonary veins running from the upper lobes seem more prominent than those running from the lower lobes.
- Kerley B lines. These are tiny horizontal lines from the pleural edge and are typical of fluid overload with fluid collecting in the interstitial space.
- "Bat's wing" haziness around the hila.
- Alveolar shadowing. In very severe pulmonary oedema fluid collects not only in the interstitial space but in the air spaces or alveoli. You can recognise this by seeing hazy shadowing throughout the lungs, and possibly air bronchograms (see future article).
Fig 2 Right-sided pleural effusion pushing mediastinum to the left |
Fig 3 Left tension pneumothorax pushing mediastinum to the right (lung edge arrowed) |
Fig 4 Left lower lobe collapse (arrow) with shift of the mediastinum to the left |
Fig 5 Left ventricular failure, see text for details |
There are only a few occasions when there may be the appearance of left ventricular failure (LVF) but a normal sized
heart - in an acute myocardial infarct (sudden onset of LVF), or lymphangitis carcinomatosa may mimic the appearances of
LVF and be accompanied by a normal sized heart.
Enlarged hila
This could be due to an abnormality in any of the three structures which lie at the hilum.
- The pulmonary artery - for example, pulmonary artery hypertension, secondary to mitral valve disease; chronic pulmonary emboli; or primary pulmonary hypertension (fig 6).
- The main bronchus - carcinoma arising in the proximal bronchus (fig 7).
- Enlarged lymph nodes - caused by infection, such as tuberculosis - spread from a primary lung tumour; lymphoma; or sarcoidosis (fig 8).
Fig 6 Primary pulmonary hypertension, both right and especially left pulmonary arteries are enlarged (arrowed) |
Fig 7 Left hilar carcinoma (arrow) |
Fig 8 Bilateral hilar lymphadenopathy (arrowed) due to sarcoidosis |
See Web Extra for our web-based x ray quiz
Next month: we will look at lung abnormalities.
Elizabeth Dick specialist registrar in radiology
North Thames Deanery
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