SOME GENERAL RULES

Bronchopneumonia.

The CXR appearances cannot distinguish between causative organisms.

Lobar pneumonia.

This is most commonly due to Streptococcus pneumoniae (pneumococcal pneumonia).

Lobar pneumonia with evidence of expansion of the lobe.

The most likely organism is either Klebsiella or Streptococcus pneumoniae.

The typical CXR patterns of bronchopneumonia and lobar pneumonia are described on pp. 32–35 and 42–44.

MIGHT THE PNEUMONIA BE ATYPICAL?

This refers to an atypical organism—usually Mycoplasma or Legionella. If this is considered to be likely then a macrolide antibiotic will be introduced.

Table 9.1 Atypical pneumonia.

Clinical/laboratory	CXR
Prodromal illness White cell count is often normal	Usually the CXR features are nonspecific Sometimes there is just a hint — i.e. multilobar involvement and pleural effusion

STAPHYLOCOCCAL PNEUMONIA

This is usually acquired within the hospital. If the causative organism is Staphylococcus aureus then flucloxacillin is introduced. Several CXR features are not specific but are nevertheless suggestive of this organism:

Patchy segmental consolidation which spreads rapidly and becomes confluent.

Cavitation within an area of pneumonic consolidation.

Development of a pneumatocoele. This occurs most commonly in children.

A pneumatocoele is a gas filled space in the lung adjacent to an area of consolidation. On the CXR it appears as a round lucent area (Fig. 9.3). A pneumatocoele is a transient CXR appearance.

Figure 9.3 Severe chest infection. The round lucent area adjacent to the left lower lobe consolidation is a pneumatocoele. Pneumatocoeles are distended air spaces that are characteristically transient—i.e. they disappear fairly quickly. Pneumatocoeles do not represent areas of cavitation. Staphylococcal pneumonia.

ASPIRATION PNEUMONIA

This may result from inhalation of gastric or oropharyngeal fluids, pus from infected sinuses, or inhalation of external fluid. If aspiration is the likely cause of the pneumonia then intravenous cephalosporin/metronidazole is added to the antimicrobial treatment. The following are suggestive of aspiration:

Clinical: an episode of reduced level of consciousness.

CXR: patchy areas of consolidation in the dependent lobes of the lung. This will not necessarily be at a lung base. If aspiration occurs when supine, then the right apical lower lobe or posterior upper lobe segments are often involved.

BACTERIAL OR VIRAL?

In general the CXR shadows do not distinguish between a bacterial or viral aetiology.

An occasional helpful hint: a combination of obvious and widespread CXR consolidation with rather minor findings on clinical examination of the lungs suggests a viral pneumonia.

PNEUMONIA WITH CAVITATION

This can occur with an acute bacterial pneumonia. The most common causative organisms are Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeroginosa, Klebsiella, Escherichia coli. (See pp. 134–137 for tuberculosis.)

Figure 9.1 Child with a chest infection. Fluffy/confluent homogeneous shadowing in the left upper lobe. Lobar pneumonia. See pp. 42–44.

Figure 9.2 Chest infection. The linear and nodular shadows in both lower zones represent the typical pattern of a bronchopneumonia (see pp. 42–44). This was a viral pneumonia.

CLASSIC PATTERNS

Pulmonary tuberculosis (PTB) is often suspected by the physician when a patient from a particular at-risk group (e.g. socio-economic/demographic) has minimal clinical symptoms and an abnormal CXR. If a patient is outside a generally accepted at-risk group then even a classic CXR PTB pattern may be misinterpreted and tuberculosis not considered.

It is important to recognise CXR patterns that raise the suspicion of PTB (Table 9.2). As a general rule, the distribution and position of PTB shadows differs between primary and post-primary disease.

Table 9.2 The most common CXR appearances.

Pitfall. CXR changes in post-primary PTB have a strong predilection for the apical or posterior segments of the upper lobes and also for the apical segments of the lower lobes. Sometimes post-primary tuberculosis shadowing will occur in the anterior segment of an upper lobe or in a basal segment of a lower lobe. This distribution may lead to the assumption that the shadows are not due to PTB. However, an apparently atypical position for shadowing in post-primary disease is usually accompanied by shadowing in the classical segments. The message: if post-primary PTB is clinically possible you must always check out the classical segments on both the frontal and lateral CXRs³.

MILIARY PTB

This represents haematogenous spread of the bacilli. It is most commonly associated with primary PTB but it can occur with post-primary PTB. The term “miliary” refers to the millet-seed appearance of the tiny nodules scattered throughout the lungs. To be truly miliary the small densities will all be of the same size (0.5–2.0 mm in diameter), sharply defined, and will usually involve the lung apices.

The visibility of these tiny nodules on the CXR is the result of superimposition of hundreds of the tiny foci one on top of another. If the number of foci are not yet in their hundreds and thousands then they will not be detectable. Consequently, a patient may have miliary PTB and yet the CXR may appear normal.

Figure 9.4 A common pattern in primary PTB. Unilateral hilar lymph node enlargement.

Figure 9.5 Classic patterns in post-primary PTB. Lung shadowing that favours the apical or posterior segments of an upper lobe (a); or involving the apical segment of a lower lobe (b, c).

Figure 9.6 Unilateral hilar lymph node enlargement (and, incidentally, the azygos node is also enlarged). Primary PTB.

Figure 9.7 Extensive shadowing, and some volume loss, in the right upper lobe. Post primary PTB.

Figure 9.8 Diffuse shadowing in both lungs with cavitation. A lateral CXR showed the apical segments of both lower lobes to be involved. Post-primary PTB. You might wish to remind yourself of the superior extent of both lower lobes on the reference images at the front of the book (p. viii.)

Figure 9.9 Numerous fine nodules (0.5–2.0 mm in diameter) are present throughout both lungs. The lung apices are not spared. Miliary PTB.

ARE THE CXR SHADOWS DUE TO ACTIVE OR INACTIVE PTB?

A recurring dilemma. A CXR shows PTB scarring—but are there any features to suggest that it could be active? Table 9.3 provides some guidelines which will help to make the assessment.

Table 9.3 Active or Inactive PTB?

Active	Probably inactive	Apply the precautionary principle:
Cavitation Ill-defined shadows Change from an earlier CXR (i.e. an increase in shadowing).	Considerable calcification with all shadows well-defined No change on serial CXRs at least six months apart	Always…careful clinical assessment and sputum examination

Figure 9.10 Note the well-defined (“hard”) shadowing at the apex of the left lung with elevation of the left hilum. These features suggest old inactive PTB affecting the upper lobe.

Figure 9.11 Ill-defined shadowing at the right lung apex. Active post-primary PTB. NB: the lung apices are where tuberculous shadows commonly occur…and they can hide behind the overlapping ribs and clavicle. On this CXR compare and contrast the appearance of the right lung apex with the entirely normal left apex.

MYCOBACTERIUM AVIUM-INTRACELLULARE

The CXR appearances are non-specific. They include: hilar and mediastinal lymph node enlargement; and/or nodular lung shadows; and/or areas of alveolar consolidation.

PTB

The most common patterns on the CXR are:

Primary PTB…lymph node enlargement; or

Post-primary PTB…apical consolidation +/– cavitation.

PNEUMOCYSTIS CARINII PNEUMONIA (PCP)

With confirmed PCP infection the CXR is abnormal in the majority of cases. The reported incidence of a normal CXR varies in different series (5–30% of cases). The common CXR patterns:

Initially…perihilar and basal fine reticular densities causing a ground glass or hazy appearance.

These rapidly develop into extensive areas of alveolar consolidation.

Some uncommon patterns do occur:

Thin walled cysts and cavities.

Discrete focal areas of consolidation.

Very uncommon findings:

Pleural effusion.

Lymph node enlargement.

Figure 9.12 Young male. Breathless. Lower zone reticular densities create a basal ground glass (i.e. a rather hazy) appearance. PCP. This is an early CXR finding and is often very subtle. Rapid progress to extensive areas of alveolar consolidation usually occurs. (Incidental body piercing artefact through the right nipple.)