Chest x rays made easy
In the fourth of a five part series, Elizabeth Dick compares collapse and consolidation of the lung and looks at pleural effusions
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.
- 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.
- 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.
- Lateral films: if the area anterior or
superior to the heart is opacified, suspect
disease in the anterior mediastinum or
upper lobes respectively. If the area
posterior to the heart is opacified suspect
collapse or consolidation in the lower lobes.
Abnormality: lobar collapse
Collapse of a lobe is caused by proximal
Obstruction - for example, by a neoplasm,
mucus plug, such as in a postoperative
patient, or foreign body, such as in a child.
Always mention that you are looking for
the cause of the collapse.
When the lobe is not aerated it will lose
much of its volume and collapse to a predictable location depending on whether
it is an upper, middle, or lower lobe.
Figure 1 shows the normal site of the
lobes of the lung; figures 2 to 5 and their
accompanying line diagrams show where
the lobes collapse to. The collapsed lobe
itself can be very difficult to see - there
may simply be a little extra shadowing on
the film. A collapsed lobe is a cause of volume loss; the other cause is a pneumothorax. The signs that should alert you to a collapse are due to the loss of lung volume:
Fig 1 Where the lobes of the lung normally lie
Fig 2 Right upper lobe collapse. Increased shadowing in
the right upper zone with a clear linear border of the
horizontal fissure which has been pulled up (arrowhead).
Note the remaining right lung is blacker than the opposite
side. In addition the hilum is pulled up. There is a mass
arising from the right hilum (arrow); this is the obstructing
bronchial carcinoma which is causing the collapse
- The mediastinum may be shifted towards the side of collapse
- The hilum is pulled up or down from where it normally lies
- The horizontal fissure will also be pulled up (in a right upper lobe collapse) or down (right lower lobe collapse)
- The remaining (non-collapsed) lung on the side of the collapse has to expand to fill the hemithorax, thus "spreading" its contained vessels; therefore the abnormal side will seem blacker with fewer lung markings than the opposite normal side
- The proximal obstruction may be visible - for example, a large carcinoma arising from the right upper lobe.
Abnormality: confluent opacification of the hemithorax
There are four main causes of confluent
opacification of a hemithorax - consolidation (fig 6) (that is, material within the
air-spaces-see November studentBMJ)
and pleural effusion - that is, material
within the pleural space, which could be
serous fluid, blood, or pus (fig 7).
Complete collapse of one lung with the
mediastinum shifting over the the abnormal side can also cause a "white out" on
the abnormal side (fig 8). Finally, after a
pneumonectomy the mediastinum shifts
to the empty hemithorax and the residual pleural space fills with fluid and
fibrotic material leaving the patient with
a complete "white out" on the side that
has been operated on (fig 9).
Consolidation and pleural effusion are
the two most common, and it can be
difficult to distinguish between them - of course, they can coexist.
Fig 3a Antero-posterior chest radiograph, left upper lobe collapse
Fig 3b Lateral. Left upper lobe collapse. Increased
shadowing in the left upper and mid zone with a blurred
lower border. The left heart border is also lost, because
the lung collapses adjacent to it. On the lateral view the
upper lobe can be seen to have collapsed anteriorly and
lies anterior to the oblique fissure (arrow)
Fig 4a Antero-posterior chest radiograph. Right middle
lobe collapse. The right middle lobe lies adjacent to the
right heart border, so the right heart outline is lost.
Fig 4b Lateral, same patient. The right middle lobe
collapses anteriorly in a wedge shape over the heart. The
upper border of the wedge is the horizontal fissure
(arrowhead), the lower border is the oblique fissure
(arrow)
Fig 5a Antero-posterior chest radiograph. Left lower lobe
collapse. The lower lobes collapse posteriorly and
inferiorly so that the contour of the hemidiaphragm is
lost. The collapsed left lower lobe may form a "sail"
shape behind the heart border on the Antero-posterior
film (arrow)
Fig 5b On the lateral film there is extra shadowing posteriorly over the vertebrae due to the collapsed lobe (arrow)
The key features of an effusion are:
- If the patient is erect there should be a fluid level and meniscus visible
- If the effusion is large the
mediastinum will be shifted to the
opposite side. Compare this with
pure consolidation in which there is no change in volume of the
hemithorax and therefore no
mediastinal shift. There is one caveat
to bear in mind, which is that if
collapse of the lung is accompanied
by a pleural effusion the loss of
volume (caused by the collapse) may
be balanced out by the increase in
volume of the hemithorax (caused by
the effusion) and therefore it may
seem as if the volume of the
hemithorax overall is equivalent to
the opposite side.
As we discussed in November the key
feature of consolidation is an air bronchogram. In infective causes of consolidation the process may affect a lobe (lobar pneumonia in a distribution according the
normal anatomy shown in fig 1) or spread
in a more patchy distribution (bronchopneumonia). Now test yourself with our
web quiz at studentbmj.com.
Next month: we will look at lung nodules and masses.
I would like to thank Dr Anju Sahdev,
Dr Brian Holloway, and Dr Robert Dick
for contributing some of the films which
are illustrated.
Fig 6a Left lower lobe consolidation. There is opacification of the left lower zone with loss of the hemidiaphragm,
indicating the consolidation abuts the diaphragm - that is, is within the lower lobe. A key feature is that there is no loss of volume. There is no mediastinal shift and no fluid level
Fig 6b On the lateral film, air bronchograms can be seen
within the consolidation which occupies the posterior
lower hemithorax-that is, the normal anatomical site of
the left lower lobe
Fig 7 Right pleural effusion. There is opacification of the
lower right hemithorax with a fluid level, and the
mediastinum is pushed to the left side
Fig 8 Complete collapse of the right lung. A proximal
right main bronchus carcinoma has obstructed the distal
right bronchus and caused complete collapse of the right
lung with the trachea and mediastinum pulled to the right
side by the loss of volume on the right. There is also a
rightsided pleural effusion, best seen superiorly. However,
the loss of volume due to the right lung collapse is
greater than the increase in rightsided volume due to the
pleural effusion so that overall the mediastinum is pulled
over to the right
Fig 9 Left pneumonectomy. The left lung contained a
carcinoid tumour and was removed. There is left sided
loss of volume with shift of the mediastinum and chest
wall (ribs) and left hemidiaphragm towards the "empty"
left hemithorax. The residual space in the left hemithorax
fills with fluid and fibrotic tissue a few weeks after
pneumonectomy
Elizabeth Dick, specialist registrar in radiology, North Thames Deanery
studentBMJ 2000;08:435-476 December ISSN 0966-6494
