CHEST X-RAYS

This introduction to the chapter is aimed at providing a systematic framework for approaching chest X-rays. Further details and examples of the specific X-ray findings discussed below are covered more extensively in the example cases later in the chapter and in the bonus X-ray chapter.

In this book we look only at frontal chest X-rays (PA and AP X-rays), as these account for almost all chest X-rays performed. The lateral chest X-ray is not commonly performed and has been largely replaced by CT.

1. Projection (AP/ PA)

The projection of a chest X-ray can affect its appearance and interpretation. Therefore it is important to determine which projection has been used.

• The two possible projections for a frontal chest X-ray are the anteroposterior (AP) and the posteroanterior (PA). Somewhere on the X-ray you should see something that indicates whether it is AP or PA.

• The PA X-ray provides the best assessment of the thorax but requires the patient to be able to stand (or sit on a stool). This is the standard projection, so if there is no annotation stating otherwise, you can assume the X-ray is PA.

• AP X-rays provide a less comprehensive assessment than PA X-rays due to the effects of magnification and the position of the scapulae (figure 1). They are usually only performed for haemodynamically compromised patients.

• If you cannot remember which one is the standard view, remember, "AP is 'crAP', so PA is standard".

• If you are asked to justify why an X-ray is PA, remember that in PA X-rays, the patient's arms are positioned in such a way that the scapulae are pulled almost fully out of the lung fields. In AP X-rays, this positioning is not possible, and the scapulae are projected further over the lungs.

2. Patient Details

• It is important to ensure you are looking at the correct X-ray from the correct patient.

• The patient's details will be on the X-ray (unless anonymised for the exam).

• Say the name, age/date of birth, and when the X-ray was taken.

• The age and gender of the patient are useful for helping to formulate your differential diagnosis.

3. Technical Quality

• Check that the X-ray includes all of the thorax (both lung apices, the lateral sides of the ribcage, and both costophrenic angles). Important pathology can be missed if the entire thorax is not imaged.

• It is unlikely that you will be given an X-ray in the exam that does not show the entire lungs, but some parts are occasionally missed in practice.

• It is important to assess RIP – Rotation, Inspiration, Penetration.

Rotation

• The heads of the clavicles (medial ends) should be equidistant from the spinous processes of the vertebral bodies. If they are not, the patient is rotated.

• Patient rotation can erroneously give the impression of mediastinal shift or lung pathology (figure 2).

Inspiration

• PA and AP X-rays are taken in held deep inspiration. Count the ribs to assess inspiratory effort.

• You should count down to the lowest rib crossing through the diaphragm. Six anterior ribs or 10 posterior ribs indicate adequate inspiratory effort.

• Fewer ribs indicate an underinspired X-ray. This may be due to the timing of the X-ray, or, more frequently, because the patient is unable to take and hold a deep breath (due to pain, breathing problems, or confusion). Underinspired X-rays can cause crowding of the lung markings at the bases, incorrectly giving the impression of consolidation or other pathology. Additionally, the heart may appear falsely enlarged (figure 1).

• More ribs, particularly with flattened diaphragms, indicate hyperinflation due to airway obstruction, such as chronic obstructive airway disease (COPD).

Penetration

• The X-ray is adequately penetrated if you can just see the vertebral bodies behind the heart.

• "Underpenetrated" means that you cannot see behind the heart and "overpenetrated" means that you will be able to see the vertebral bodies very clearly.

• Over and under penetration can obscure or obliterate significant findings, particularly in the lungs.

• This is less of a problem with the advent of digital viewers which allow the X-ray "windows" to be manipulated. However, this function can only manipulate the image so far, so adequate penetration is still important.

4. Obvious Abnormalities

If you can see obvious abnormalities, say so and describe them:

Which lung is involved?

Which part of the lung?

• If possible, say which lobe is/lobes are involved. Remember it is not always possible to determine this on an X-ray – in which case use upper, middle, or lower zone to describe the abnormality's location. CT can locate abnormalities more accurately.

Size

Shape

• Is it focal or diffuse, rounded or spiculated, well or poorly demarcated?

Density

Describe the density of an abnormality in relation to the normal surrounding tissue, e.g. if the abnormality is in the lung, compare it to the normal lung; if in the bone, compare it with the other bones.

If the abnormality is denser (i.e. whiter) than the normal tissue, you can say that there is increased opacification or density; if less-dense (i.e. blacker), say there is increased lucency or reduced density.

Texture

You should assess whether the abnormality has a uniform or heterogenous appearance.

Other features

• If there is anything else in the abnormality, such as air bronchograms or fluid levels, then mention these as well.

• Are there other abnormalities, such as volume change, bony abnormalities, or surgical clips?

5. Systematic Review of the X-ray (Figure 3)

• Initially assess from a distance to see differences in lung shadowing/obvious masses. Previously, when using hard-copy X-rays, you would be taught to look at the X-ray initially from four feet; however, now most X-rays are viewed on computer so make sure you zoom out as much as possible for your initial inspection.

• After that, reassess from close-up to look for subtle abnormalities.

• It does not matter what system you use for assessing the X-ray, as long as you do not miss any areas.

• A useful system is ABCDD (Airway, Breathing, Circulation, Diaphragm/ Delicates).

• Also comment on manmade abnormalities, e.g. lines, pacemakers, a nasogastric (NG) tube.

A – Airway

• Is the trachea central?

• If not, is it deviated due to patient rotation or pathology?

• If the cause is pathological, is the trachea...