Intro to CXR 1. Download the presentation for best effect (animations don't function properly online).

1. Introduction to
Chest X-ray Interpretation
RAH Radiology

2. How to interpret CXR:
• Film quality
• Anatomic structures
• Basic patterns of disease
Warning:
This is a big topic. Important phrases and
concepts are bolded.

3. Film quality:
• Position
• Rotation
• Penetration

4. Film quality:
• Position
• Rotation
• Penetration
This is a frontal chest xray.
This is a posteroanterior (PA)
projection.
• The X-rays are generated behind the
patient, and strike the film/screen in
front of the patient.
• This reduces magnification of the
heart, which is at the front of the
chest.

5. Film quality:
• Position
• Rotation
• Penetration
This is a frontal chest xray.
This is an anteroposterior (AP)
projection.
• CXR are always performed PA unless
the patient is too unwell to stand.
• On AP films the heart is exaggerated
in size, and the lungs are usually
under-inspired. AP films are generally
poor quality and harder to interpret.

6. Film quality:
• Position
• Rotation
• Penetration
There are many other aspects of
positioning, which can affect
assessment. Examples include
degree of lordosis (hunching
forward) and quality of inspiration.
There is suboptimal inspiration on
this film, which makes the heart
look bigger (by tilting the axis) and
increases lung density (less gas
present).

7. Film quality:
• Position
• Rotation
• Penetration
This film is rotated.
Click forward to see why.
Rotation can distort normal
structures and alter how dense the
lungs appear.
The spinous processes should be centred
between the heads of the clavicles.
The lateral soft tissues should be the same density.
More dense
Less dense

8. Film quality:
• Position
• Rotation
• Penetration
This film is poorly penetrated.
Everything is grey and washed out.
You can’t see the spine through the
heart.
Assessment is difficult (spine,
retrocardiac lung etc.)

9. How to interpret CXR:
• Film quality
• Anatomic structures
• Basic patterns of disease

10. How to interpret CXR:
• Film quality
• Anatomic structures
• Basic patterns of disease

11. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
• For example, an enlarged heart
suggests you should look for
APO, but pneumonia is unlikely
to affect the mediastinum.
It is up to you which approach to use,
but we suggest:
Mediastinum -> Hilar regions -> Lungs ->
Pleura -> Chest wall

12. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
The mediastinum and hilar regions
will be covered in more detail next
session.
For now, just assess heart size using a
rough guesstimate – more or less
than 50% of the chest width (rib to
rib).

13. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
The lungs are only partially seen on
frontal films, and extend behind the
mediastinum and diaphragm.
While lobar divisions are often
taught, they are not prognostically
useful. It is simpler to describe
upper, middle and lower lung zones
when you are assessing a frontal xray.

14. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
The lung vessels are seen as curving
lines. They divide every few
centimetres, largest centrally and
roughly halving at each division.
You should not be able to identify
vessels in the peripheral lung.
Gravity pulls blood to the lower zone
vessels, so they are larger than the
upper zone vessels.

15. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
The connective tissue between the
airspaces is the pulmonary
interstitium. This can be seen as fine
lines criss-crossing the lung fields.
Unlike the vessels, these lines are
consistent in thickness, and should
reach the lung periphery. Normal
interstitium is almost invisible.

16. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
We will review the pleura next
session.
For now, just look for blunting of the
costo-phrenic recesses on erect
films.

17. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
We will review the bones and soft
tissues next session.

18. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
The lateral chest xray is under-
appreciated. It is very useful for
finding hidden pathology and
localising abnormalities.
It is also difficult to orientate
yourself to without practice.

19. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
You can approach the film the same
way as the frontal film.
The heart / mediastinum extends
between the sternum towards the
spine, but the posterior border of the
heart should be greater than half a
vertebral body width away from the
spine. Any closer suggests
cardiomegaly.

20. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
The hilar regions can be appreciated
by identifying the left and right
pulmonary arteries.
Lymphadenopathy is often well
demonstrated on the lateral film.
The left pulmonary artery is
posterior to the right.

21. Anatomic structures:
• Radiologists use an “in-to-out”
approach. Review the central
structures first, the peripheral
structures last.
• This approach best matches the
patterns of pathology, which
aids interpretation.
The vertebral bodies are well seen,
and crush fractures are easier to see
than on the frontal projection.
The vertebral bodies appear
progressively less dense the lower
you go down the chest, until the
diaphragm. If the lower bodies
appear dense, it is often due to
pulmonary opacity like pneumonia.

22. How to interpret CXR:
• Film quality
• Anatomic structures
• Basic patterns of disease

23. How to interpret CXR:
• Film quality
• Anatomic structures
• Basic patterns of disease
• Lung Pathology
• Mediastinum (next week)
• Pleural disease (next week)

24. Click to highlight the abnormality.
Increased opacity can be divided
into interstitial and alveolar
densities.
These can be described as “lines”
and “clouds” respectively.
This is an example of cloudy
(alveolar) density.
High density lung pathology:
Look for asymmetric or otherwise
abnormal density:
• “There is increased density at
the left lung base”

25. High density lung pathology:
Look for asymmetric or otherwise
abnormal density:
• “There is increased alveolar
opacity at the left lung base”
Alveolar opacities are caused by
filling of the terminal airspaces
(alveoli).
Alveoli can be filled with simple fluid
(alveolar oedema), pus
(pneumonia), blood (pulmonary
haemorrhage), vomit (aspiration) or
cells (some forms of malignancy).
Reduced aeration (collapse) can
have a similar appearance.

26. High density lung pathology:
Look for asymmetric or otherwise
abnormal density:
• “There is right upper lobe
collapse with elevation of the
horizontal fissure”
Collapse typically causes volume
loss, that is, the surrounding
structures are pulled inwards.
Filled alveoli (called consolidation)
should not cause volume loss,
although there is usually an element
of collapse seen with consolidation
(i.e., mucous plugging in
pneumonia).

27. High density lung pathology:
Look for asymmetric or otherwise
abnormal density:
• “There is left upper zone
consolidation with air
bronchograms”
Consolidation often demonstrates
air bronchograms. The alveoli are
filled, but the bronchioles remain
aerated, so you see low density
tubular structures superimposed
over the opacity.
Air bronchograms should not be
seen with collapse.

28. High density lung pathology:
Look for asymmetric or otherwise
abnormal density:
• “There is increased linear
density throughout the lungs.”
Interstitial opacities are caused by
thickening of the normal pulmonary
connective tissue (the interstitium).
The alveoli remain aerated, so the
thickened interstitium is outlined by
gas. Therefore, we see increased
linear or reticular density.
Click for a zoomed in view of the
increased interstitial markings.

29. High density lung pathology:
Look for asymmetric or otherwise
abnormal density:
• “There is increased interstitial
opacity throughout the lungs.”
Increased interstitial opacity can be
caused by heart failure,
inflammation / infection, fibrosis or
malignancy.
Interstitial opacities can be difficult
to appreciate, particularly because
they are often symmetrical.

30. An example case:
Description?
• Too many lines?
• Clouds?
Interpretation?

31. An example case:
“This is an AP film with poor
penetration showing an enlarged
heart and widespread increased
interstitial opacity. There is also
left basal alveolar opacity.”
This is acute interstitial oedema
with cardiomegaly.
The left basal opacity obscures the
left hemidiaphragm, consistent
with collapse or consolidation
(common in unwell patients due to
decreased depth of breathing, but
can’t exclude infection).

32. Film the next day, after treatment:
Description?
• Too many lines?
• Clouds?
Interpretation?
Does this support our earlier
diagnosis?

33. Film the next day, after treatment:
“This is an AP film with poor
penetration showing an enlarged
heart. There has been interval
resolution of the interstitial and
alveolar opacities.”
The rapid improvement in the
appearance on chest xray following
treatment is an important feature
to discriminate pulmonary oedema
from other interstitial processes
such as atypical infection.
Left basal alveolar opacity also
often resolves as the patient
improves, because they can
breathe more deeply.

34. Click to highlight the abnormality.
Mass lesions typically look like
rounded, well defined clouds. This
makes sense, as the airspace has
been replaced.
Mass lesions can be benign or
malignant, and it can be hard to
differentiate. Larger lesions,
multiple lesions, and new lesions
are more likely to be malignant.
High density lung pathology:
Look for asymmetric or otherwise
abnormal density:
• “There is a rounded mass at
the left midzone / hilar region”

35. Click to highlight the abnormality.
Air-fluid levels in masses suggest
cavitation in cancer (particularly
squamous cancer) or abscess
formation. Other causes are rare.
Clinical history is usually very useful
to discriminate between these.
High density lung pathology:
Look for asymmetric or otherwise
abnormal density:
• “There is a rounded mass with
an air-fluid level at the left
midzone”

36. Low density lung pathology:
Look for asymmetric or otherwise
abnormal density:
• “There is generalised lucency
and prominence of the
bronchovascular markings,
consistent with emphysema”
Hyperlucent lungs suggest there is
less tissue within the volume. This is
usually cause by emphysema.
Associated findings are
hyperexpansion of the lungs with
flat hemi-daphragms, and increased
visibility of the vessels (“coarse
bronchovascular markings”).

37. Low density lung pathology:
We will cover the other major low
density thoracic pathology
(pneumothorax) next session with
pleural disease.