An Introduction to Chest Radiology by itlpw9937

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									                            An Introduction to Chest Radiology

This is a simple introduction of the key concepts necessary to interpret a chest
radiograph. Here lies the basic facts of how a chest xray is taken, what different shades
of black/grey/white actually mean, some suggestions for how to go about examining and
describing a chest xray and a discussion of how you might make a management plan
based on the information on the film.

    1.   Normal chest anatomy
    2.   Taking chest films
    3.   Guide to interpretation
    4.   Management principles
Section 1: Normal Chest Anatomy

Figure 1.1 A standard PA film of a normal chest xray of an adult male.

1.1 - Overview

On examining the film initially, it is worth taking a step back, highlighting the key
features - e.g. "This is a PA/AP chest radiograph of a young/old adult female/male". This
will start you thinking of appropriate pathologies to rule out as you go around the
radiograph itself. Don't forget to check the date of birth for approximate age, see if there
are soft shadows of breasts (one breast only following mastectomy may be the whole
point of the film). Depending on who is examining you, you will be guided as to how
much detail is needed here.

A system is a useful thing to have in your head. In the Student BMJ, Elizabeth Dick[1]
suggests a system for review of the chest radiograph, starting from the trachea and
moving down the patient’s left, then across and up on the right hand side, which I
summarise here. You need some sort of system to remember the components of the
radiograph to go through, but the exact one you pick is up to you. I like this system as it
seems logical and easy to remember.

Trachea – is it central?
Left heart border – aortic arch, left heart = left atrium and left ventricle
Left hilum - pulmonary artery branches fanning out, bulky?
Heart proportions – 2/3rds on the left, no more than half of the chest cavity in width
Right heart border – right atrium
Right hilum – pulmonary artery branches fanning out, bulky?
Lungs – start from apices, comparing both sides and working down. Focus on apices
and peripheries, especially scan for a pneumothorax
Hemidiaphragms – should curve downwards, right higher than left, costophrenic
angles, cardiophrenic angles, no free air under the diaphragm (perforation of viscus in
the abdominal cavity, not to be missed)
Soft tissues and bones -> both breasts present? ?Mastectomy, broken rib?

1.2 - Anatomical areas in detail

The trachea:
Is it central? If the trachea is off to one side to a large extent, typically this will be
attached to the rest of the mediastinum, so that the heart will be shifted to one side as
well. This should make you think of pathologies that cause gross movement of tissues,
e.g. a tumour or a tension pneumothorax. The history will guide the prioritisation of your
differentials. The trachea can be slightly to the right in a normal xray, and interpretation
is dependant on rotation (see section 2).

The heart:
Is it large? This should be less than half the total width inside the ribcage. A large heart
("cardiomegaly") could be due to hypertension or heart failure amongst other things.
Following the heart shadow from the trachea down the left side of the heart, we go past
the aortic arch, the left hilum, the left heart border (including the left atrium and
ventricle) until we reach the left cardiac angle
Is it in the right place? About 1/3 should be to the right of the vertebrae, 2/3 on the left.
Deviation suggests tumour/tension pneumothorax

The hila:
One each side, the left is slightly higher than the right. This is where the vessels enter/
leave the lungs, and is a site of many lymph nodes. If there are bulky structures here
they are likely to be lymph nodes, so think maybe lung malignancy or lymphoma,
depending on history.

Lung fields:

Are the lung fields symmetrical?
First we check for gross asymmetry, e.g. a large white-out of part of the lung, or one
lung than is grossly larger than another. There are patterns associated with lung
collapse, depending on which lobe is collapsed, which should be learnt (in later section).

Do the markings go all the way out to the edges of the lungs?
If there are no markings in any part of the lung fields, this raises our suspicion of
pneumothorax (particularly if the film is of a young, fit, tall male). It should be possible
to see where the lung has been pushed away from the ribcage -> a section of no
markings around the edge of the lung field.

Are there any unusual markings?
Consolidation -> if one of the lobes is whiter than the others, think collapse or
consolidation. Consolidation means fluid in the small airways of the lung. If you look
closely you may see an "air bronchogram" which is where you see an air-filled space
(black) of the larger airway (which is not full of fluid itself) against the whiter area of the
fluid-filled small airways. This fluid could be anything, radiologically. Although clinically
consolidation is used interchangeably to mean infection (where the fluid is the
inflammatory exudate), it could also mean blood, lymph fluid etc. However, if you spot
consolidation and don't mention infection (e.g. lobar pneumonia), this is an oversight.

Reticulo(-nodular): lines in the lung fields - very small white lines. This is pathognomic
of interstitial lung disease. The small lines spread to the edges of the lung fields, but
may be more noticeable in the central areas. "-nodular" means the apparent nodules
where the lines intersect, but there are no actual nodules.

Nodular: Small splodges of white, often widespread, can mean widespread infection,
most importantly TB.

Ground glass: Interstitial lung disease or respiratory distress syndrome in an infant.

Abscess: A fluid level in a cavity might well be an abscess, caused by infection /

Kerley B lines: Horizontal white lines seen in heart failure at the costophrenic angles and
above, mm-cm across. These are synonymous with heart failure. Look for them if you
suspect heart faliure (from cardiomegaly). Also look thereafter for "upper lobe diversion"
whereby the upper pulmonary arteries are unusually clear. And for pulmonary oedema
(a bat-wing like appearance of diffuse whiteness in the peri-hilar region).

Are the hemidiaphragms level? Normally the right is slightly higher than the left. Use
your experience to judge it. If there is tenting of one of the hemidiaphragms this can be
due to malignancy, which pulls the diaphragm up towards it.

Costophrenic/cardiophrenic angles -> Angle between the rib and the diaphragms / angle
between the heart and the hemidiaphragm. These should be sharp. If not, think pleural
effusion, i.e. fluid in the pleural space

Check under both hemidiaphragms for air, which is a vital thing to spot. Air under the
diaphragm means a perforated viscus until proven otherwise. This may be a bowel,
peptic ulcer, or post-laparoscopy(CO2 not yet absorbed). Try not to mistakenly confuse
this with the gastric bubble, which is actually in the stomach, rather than forcing the
diaphragm away from the stomach/liver. Particularly important in general surgery.

Soft tissues:
Sometimes an abnormality may be seen in the soft tissues, e.g. post-mastectomy.

If all else fails, follow the cortex of the ribs, clavicles, vertebrae, etc. to see if there are
any cortical discontinuities. It is not common to see this on CXR, but if the history is of
trauma, this is worth considering.
Section 2: Taking Chest Films

2.1 - Basic details and terminology

PA vs AP:
These terms refer to the direction that the xrays themselves take through the patient. A
"PA" (posterior->anterior) film involves the patient facing away from the xray camera,
with the film itself in front of them. The patient can lift their arms over the film, reducing
the amount of shoulderblade that overlaps the main thoracic area. A PA film is the
standard outpatient xray, or walking patient xray, and is taken when standing. A very
sick patient is unlikely to have a PA xray.

An AP film is usually taken supine - when a patient is very ill, or unable to get out of
bed. A typical example is one taken in A&E in the resuscitation room. The patient's
shoulderblades take up more of the thoracic cage, obscuring pathology in the upper
outer areas. The heart looks rather large, because the camera is nearer to the heart. It
is said that you should not interpret how large the heart is on an AP film, because of
this. However, in reality if the heart is really very large, it is worth commenting on

If a patient has an AP film, there will often be ECG leads in the xray from A&E resusc.
Use this knowledge and if you see ECG leads, check to see if it is an AP film before you
go on.

Lateral films:
Very rarely, it will be considered useful to order a lateral chest radiograph. They are hard
to interpret and it would be a surprise to get one in an OSCE. If you want to read up on
them feel free, but they won't be covered farther here.

In a typical PA film, the film is taken in full inspiration, which maximises the expansion of
the lung fields on the radiograph, making for clearer analysis. If such a full breath has
been taken, there should be 6 anterior ribs / 9 posterior ribs visible above the
hemidiaphragm. Some people go into more exacting detail as to whole ribs/which part of
the diaphragm is included, but this is less important. If there are more than this number
of ribs, the patient is said to be hyperinflated, and you may think COPD / asthma. If
there are noticeably fewer ribs visible, we must think either a) poor inspiratory effort or
b) pathology causing a reduction the apparent lung fields, e.g. tumour

A film is adequate if it covers the region we are interested in, i.e. if all of the lung fields
including apices, ribs, area under the diaphragm, costophrenic angles are included in the
film. If we are missing part of a lung, you should really comment on this, since typically
we would repeat this xray.

Check the medial ends of the two claviclese. If there is a big gap between one of the
medial ends of the clavicles and the vertebrae then you may say that the film is rotated,
e.g. the camera is not perpendicular to the patient, we are looking from an angle. This
means one lung field is closer to the xray emitter than the other, and will affect how it
looks. It's not worth commenting unless there is significant rotation, since a) normally
there won't be much rotation as this is one thing the radiographer is trying to avoid and
b) a small amount of rotation makes very little difference to interpretation. There are not
many common pathologies to be picked up on in terms of rotation, but if one lung field
looks whiter than the other, it is worth checking rotation to see if this is the cause.

A film is said to be adequately penetrated if you can see the some of the outline of the
lumbar vertebrae behind the heart. It is over-penetrated if they are too clear, under if
you cannot see them at all amidst the whiteness. Xrays themselves make the film
blacker. So a poorly penetrated film will be whiter than a overpenetrated film, which will
be black.
Section 3: Guide to interpretation

3.1 - Describing common abnormalities

There are a number of key phrases that carry weight in radiology, and it is important
when and how to use them. It is important to pick the right one, or your examiner will
think you have misinterpreted the xray.

Grossly, you may remark on "increased opacity" or "decreased opacity" which is pretty
safe, and clear what you mean. Sometimes "white lung" or "black lung" are appropriate.
These expressions show the examiner you have noticed the abnormality without
narrowing down the exact pathology, which is useful to gain their confidence and buy
time whilst you think of what the exact pathology may be.

When practising and presenting radiographs, sit on your hands (at least in your mind!) It
is not acceptable to point unless description with words has failed (not a good thing).
After all, radiologists reporting on xrays are not there to point out abnormalities when
you see their reports! The zone that the abnormality is in is a useful concept. E.g. "a
patchy lesion in the mid zone of the left lung" is acceptable.

Terms such as consolidation, reticulonodular, nodular, cannonballs, cavitating lesion etc.
are specific, and you should use them only when you are sure that is what you are

Some terms are specific only the the radiological entity, not to an actual pathology. E.g.
"cavitating lesion" is specific to the appearance on xray of a hole (a cavity) in the normal
lung tissue (the lung parenchyma - the functional part of the lung), but could represent
TB, a staph infection, malignancy (primary or secondary), an abscess, an infarction,
even a rheumatoid nodule.

If looking for a word for a general "thing" or "something" on the xray, you can't go far
wrong with the word "lesion"!

If searching for where a lesion may be, say "zone". Split each lung into upper, mid and
lower zones, approximately a third each. This is terminology radiologists will understand,
and is to do with radiological appearance only, not anatomy. E.g. a lesion in the mid
zone is not necessarily in the middle lobe, it could also be in the lower lobe for
example. By saying the zone you let the examiner know you have seen it and that you
are both talking about the same lesion.

3.2 - The Physics of Chest Radiology

The important thing to remember about interpreting xrays is that you can only make out
detail when components of different densities are next to each other. (In normal vision
we find it hard to see things that are similar in colour too - the principle behind army
camouflage). Typically we can see the bones only as they are seen adjacent to lung
tissue which is of a different density. We see lung tissue only as it is next to air, etc.

The different components come up as different shades of white/grey/black, in that they
absorb more/less/hardly any xrays on the way through, respectively. Xrays blacken
films, remember.

Metal - bright white
E.g. ECG crocodile clip or sticker. Anything that is a really bright white, whiter than the
bones, is man made. Metal objects let hardly any xrays penetrate through them to get to
the film, hence show up as white.

Bone - white
For example ribs, spine, clavicles, scapulae etc. Like in all xrays the outer portion
(cortex) of the bone is whiter than central trabecular portion of the bone, since it is
denser and blocks more of the xrays. If you are looking for a fracture follow the line of
the cortex and look for discontinuities.

Soft tissue - grey
Coming between the bone and air in density, soft tissue absorbs some of the xrays as
they pass through it. This means it appears grey on the film. The soft tissue shadows of
the patient's body can give you a clue to body habitus (e.g. the weight), the gender
(look for breast shadows), and may represent the whole pathology in the xray - e.g. a
post mastectomy xray checking for lung pathology.

Soft tissue includes the lung parenchyma (the main 'stuff' of the lung, the functional lung
tissue), and is therefore very important in xray interpretation.

Air - black
Xrays pass through air easily and blacken the film strongly in these areas. Air is very
important in chest xrays as it is adjacent to the lung parenchyma, and without air as
contrast we wouldn't see any change in the fabric of the lung tissue.

Also obviously the chest xray is a 2d image, so we can't see behind the heart very easily,
as the heart has already slowed the passage of xrays through it.
Section 4: Management principles

Discussion of the radiograph will usually include discussion of the management of the
patient. The best place to start is whether the radiograph is of an acute or chronic
clinical condition. If acute, you will be starting with an ABC approach. If chronic you will
state that you would take a full history and a careful examination, request old films for
comparison. So, how do you tell?

Hopefully you will have gone through the xray by this point, and will have a good idea as
to the pathology, so you will basically know. Pointers if you are not sure are xrays taken
in the Emergency Department resuscitation room commonly involve 3 lead ECGs, and
are usually taken supine since patients are too sick to stand for their xray.

4.1 - Acute management approach

Figure 4.1 - Example acute xray - note the ECG leads

Acute - more likely if the xray has a 3 lead ECG on it, if it is taken supine (rather than
standing), AP and has an acute pathology like a pneumothorax that you may already
have spotted.

The management of an acutely ill patient considered via the medium of a radiograph is
the same as that for any acutely ill patient, e.g.

- ABC approach: Airway (oxygen as support), breathing, and circulation e.g. the ATLS
protocol. Particularly with chest conditions, oxygen is an important early intervention
over a widespread range of pathologies. ABGs are very useful in breathless patients.
- Get appropriate senior help - e.g. A&E senior doctor, nurses, etc.
- And then situation/pathology dependent (more detail in sections on specific pathology -
e.g. salbutamol for asthma, thoracocentesis for tension pneumothorax etc.)
4.2 - Chronic management approach

Figure 4.2 - asbestosis - an example of a long standing pathology.

A stable condition will typically have a standing PA chest xray, with longstanding
pathology that you may already have mentioned.

- Full history
- Careful examination
- Review old films to assess progression of pathology
- Further investigations - simple bloods, maybe an ABG, other imaging such as lateral
films, perhaps CT, then other types of investigation like lung function tests, CTPA, etc as
- A discussion of treatment options, including conservative, medical (perhaps inhalers
and steroids in COPD or antiobiotics in TB) and surgical (perhaps drainage of an
abscess), where you can think of options.
Tailor it according to the pathology you have found. E.g. in a patient with pleural
plaques, you would want to be careful about occupational history. In a patient with a
healed broken rib you would want a trauma history, and examine for tenderness or skin
changes in that region.


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