The chest x-ray is commonly performed because it is quick, inexpensive, and exposes patients to low levels of radiation. It allows visualization of the lungs, bones, soft tissues, fat, and gas/air due to the natural contrast between these structures. Reading chest x-rays requires sorting through the overlapped anatomy projected onto a single image. Systems are used to methodically check each anatomical structure. Findings of congestive heart failure on chest x-ray include cardiomegaly, pleural effusions, and signs of pulmonary edema such as Kerley lines. This patient's chest x-ray shows enlarged upper lobe vessels indicating mild congestive heart failure.

1. CHEST X-RAY

2. The plain CXR is the most commonly performed imaging exam
because:
– Cardio-pulmonary disease is common
– The exam is quick, easy to do, cheap, with low radiation exposure (a PA
CXR gives only about 3-days-worth of radiation exposure we get
anyway from natural sources)
– Most importantly the contrast elements involved allow us to see the
common pathologies we’re looking for
It’s all about the contrast: For any imaging exam to be useful, there
must be contrast (signal difference) between lesion and surrounding
tissue
There are 4 tissues that have densities that can be distinguished
from each other (have contrast) on plain X-ray:
– Calcium (bone)
– Soft tissue and fluid (not distinguishable on plain X-rays)
– Fat
– Gas/air
The natural contrast agent of air in the lungs allows us to see the
common soft tissue/fluid pathologies (pneumonia, lung CA, pleural
effusion, Kerley lines, etc.)

3. The difficulty in reading a CXR is that it’s a 2-
D representation of a 3-D object, with
everything front to back (the z-axis) projected
into a single x,y planar image
The task of reading a CXR requires sorting
out each important individual piece of
anatomy from the overlapped jumble
This requires a “system” for methodically
checking each of the individual pieces the
same way each time so that important
findings aren’t missed
Any system is just a crutch to help you
remember everything you’re supposed to
check

4. Any system that works for you is fine
Suggested system:
– White things (bones, man-made things like
tubes, pacer wires, clips)
– Gray things (soft tissues of neck/chest
wall/under diaphragm, pleural surfaces,
mediastinum)
– Black things (lungs, including lung seen
through heart and diaphragm)

5. Following image is normal PA CXR
Note that X-ray consists of overlapping
areas of varying opacity which are often
separated by edge shadows (e.g., edge of
heart with lung, edge of rib with soft tissue)
What creates an edge shadow? Two
criteria need to be met:
– 2 different tissue opacities (calcium, soft
tissue/fluid, fat, air) next to each other
– X-ray beam contacting the interface between
the 2 opacities tangentially

7. Following image is normal lateral CXR
Principle of plain X-ray is to try to get at
least 2 projections (to overcome the z-axis
overlap problem)
Note that there are 2 hemidiaphragm and
2 costophrenic angle edge shadows.
Note retrocardiac lucency (the spine
should get darker as it is followed down to
the diaphragm)

9. On a lateral CXR what would cause loss of the retrocardiac
lucency and loss of the edge shadow of one hemidiaphragm,
and why?
There must be violation of one of the 2 criteria that allow you
to see the edge shadow in the first place. Because the
diaphragm is usually dome-shaped, criterion #2 (tangential X-
ray) won’t usually be violated, so it’s probably that criterion #1
is no longer met (there has been equalization of density at the
point where the X-ray is tangential to diaphragm)
This could be caused by something of same density as
diaphragm displacing the air-containing lung away from
contact with diaphragm (pleural effusion)
Or it could be caused by a process within the lung casing it to
become same density as diaphragm (consolidation such as
pneumonia, atelectasis)
Vast majority of basilar opacities on CXR are due to pleural
effusion, consolidation, atelectasis, or a combination of these

10. How does one distinguish among pleural
effusion, consolidation, and atelectasis?
(the causes and treatments are different)
Classic sign of pleural effusion on CXR is
a meniscus (a sharp edge between the
fluid and adjacent lung). In general, a
sharp edge between the lung and anything
suggests that a pleural surface is being
crossed.
Classic sign of atelectasis is evidence of
volume loss (shift of fissures or
mediastinum, diaphragm elevation)

11. Following 2-view CXR shows RML
pneumonia
Note opacity that obscures right heart border
on PA (because RML opacity causes
equalization of density at point where X-ray is
tangential to right heart)
On lateral, note sharp inferior edge shadow
of the pneumonia (this is major or oblique
fissure pleural edge with X-ray tangential to 2
different densities)
Note hazy, fuzzy superior edge to the
pneumonia, because it doesn’t involve the
whole RML up to minor (horizontal) fissure. If
it had, it would have had a sharp top edge
shadow also.

14. Following PA CXR shows left base opacity behind
heart (retrocardiac lucency is absent), and
expected edge shadows of left hemidiaphragm,
descending aorta, and lower lobe pulmonary
vessels are all absent
Of the big 3 basilar opacity diagnoses, this is
atelectasis because there are associated signs of
volume loss (mediastinum shifted left, left
hemidiaphragm elevated)
Leftward shift of mediastinum is real and not
because of rotation (spinous processes are
midline between medial heads of clavicles)
This post-operative patient had a mucous plug
occluding the left lower lobe bronchus (note the
post-op free air under the right hemidiaphragm)

16. Atelectasis and lung collapse mean the same
thing (airlessness and loss of volume of a
piece of lung)
Atelectasis (collapse) may involve a
subsegment of lung, a whole lobe, or even a
whole lung)
Atelectasis (collapse) is different from
pneumothorax, an example of which is on the
following CXR
Although lay language may call a
pneumothorax a collapsed lung, medically
atelectasis (collapse) does not imply any air
in the pleural space

18. On the following lateral CXR, not the
posterior retrocardiac basilar opacity which
obscures one hemidiaphragm edge
shadow
The obscured hemidiaphragm is the left
(identified because of the bowel under it)
This is left lower lobe atelectasis (collapse)
because of the associated volume loss
(elevated left hemidiaphragm)
This is the lateral CXR that goes with the
PA CXR of LLL collapse already shown

20. The 2 following images are a normal 2-
view CXR
Note the normal basilar/retrocardiac
lucency and normal hemidiaphragm edge
shadows

23. Following 2-view CXR is of same patient
who had the preceding normal CXR, but at
a later time
Note the left base retrocardiac opacity,
loss of LLL edge shadows, and volume
loss on left
This is LLL collapse due to mucous plug in
asthmatic

26. Following 2-view CXR is same asthmatic
patient on a different ED visit
Note right base retrocardiac opacity, loss
of RLL edge shadows, and volume loss on
right
This is RLL collapse

29. Following CXR shows opacity medially at
apex of right chest
Note sharp lateral edge of the opacity
suggesting a pleural surface tangential to
X-ray, an elevated minor fissure
There is associated elevation of right
hemidiaphragm
This is case of RUL collapse

31. Following 2-view CXR show an opacity
adjacent to right heart with obscuration of
right heart border
This is RML collapse because lateral
shows two sharp pleural edge shadows
(major and minor fissures) which have
moved close to each other as the RML
between them has collapsed
The wide mediastinum in this case is just
due to a tortuous aorta in an elderly
patient

34. Following 2-view CXR shows a left chest
opacity
Left heart border is obscured and
retrocardiac lucency is preserved,
indicating that opacity is anterior in
location of LUL
Note sharp edge shadow of left major
fissure on lateral
Leftward shift of mediastinum indicates
LUL collapse (due to lung CA, see
narrowing of trachea and left mainstem
bronchus due to adjacent adenopathy)

37. Following case shows complete
homogeneous opacity of left hemithorax (no,
patient did not have a pneumonectomy)
Differential diagnosis is between a massive
pleural effusion (so large that it compresses
underlying lung) and a completely collapsed
left lung
Volume loss on left (mediastinal shift,
elevation of left hemidiaphragm) indicates
complete collapse of left lung
Massive pleural effusion takes up space and
would shift mediastinum to right.

39. Following CXR shows complete opacity of
the lower 2/3 of right chest
The opacity forms a sharp edge shadow
with the RUL and extends lateral to the
RUL
The sharp edge shadow indicates a
pleural surface, placing the opacity outside
lung, in pleural space
This is a large pleural effusion, showing
what is essentially a high meniscus.

41. Following CXR is same patient as
preceding, but following a thoracentesis
Right effusion is much smaller, but not
gone, and there is now pneumothorax as
well, a hydropneumthorax (note the air-
fluid levels)
In spite of drainage of most of the effusion,
there is still nodular thickening of the right
pleural surfaces, secondary to tumor
implants in this patient with malignant
mesothelioma, secondary to prior
asbestos exposure

43. Another CXR on same patient shows
progression of mesothelioma encasing
entire right lung (over a year later)

45. Following CXR on 70-year-old female
patient who complains of shortness of
breath climbing one flight of stairs,
worsening over last couple weeks. Had
been smoker until 5 years ago when she
had small MI

47. History suggests CHF
Findings of CHF on CXR in general
– Cardiomegaly (width of heart greater than 50% of
width of lungs at widest point, on standard 6-foot
upright PA CXR with good inspiration and not rotated)
This is actually assessment of cardiac silhouette, so
remember possibility of pericardial effusion
Don’t apply 50% rule without allowing for any non-standard
factors
– Pleural effusions
– Pulmonary vessel enlargement (especially upper lobe
vessels on upright CXR)
– Pulmonary edema
Interstitial edema (Kerley lines, peribronchial cuffing, fuzzy
vessels)
Alveolar edema (symmetrical air-space infiltrates, diffuse or
perihilar/bat wing)

48. On this patient’s CXR (standard upright
PA), cardiac silhouette size is borderline
(50%)
She has no visible pleural effusion
No visible pulmonary edema (not
surprising since she is only symptomatic
with exercise)
However, she does have upper lobe
vessel enlargement (compare to following
CXR which patient had done 2 months
before she became symptomatic)

50. Following image is magnification of upper
lobe vessels when patient was
asymptomatic
Note typically thin upper lobe vessels seen
on upright CXR

52. Following image is magnification of upper
lobe vessels when patient was
symptomatic
The same upper lobe vessels are now
much more dilated
Patient has mild CHF, although not
pulmonary edema

54. Following CXR and 2 magnified views shows patient
with CHF and interstitial pulmonary edema
Be careful about calling a large cardiac silhouette on
this AP supine CXR, but allowing for non-standard
factors, considering that patient is thin and has taken a
very good inspiration, the silhouette is large
The images show a good example of Kerley lines
– Kerley B lines are lines measuring no more than about a
cm, oriented perpendicular to the pleural surface at the
edge of the lung
– The lines are most visible inferiorly (hydrostatic pressure)
– Kerley B lines are thickened interlobular septa, separating
the secondary lobules of lung (small ~1cm subunits of
lung)
– The septa are thickened because of edema, and dilatation
of lymphatics and pulmonary venules which run in the
septa