22 SUSPECTED COPD

Chronic obstructive pulmonary disease (COPD): Disease characterised by the presence of airflow obstruction due to either chronic bronchitis or emphysema.

image Chronic bronchitis is defined clinically: A chronic productive cough on most days of the week for three months of the year in each of two successive years in a patient in whom other causes of chronic cough have been excluded.
image Emphysema is defined anatomically: Abnormal permanent enlargement of air spaces distal to the terminal bronchioles, accompanied by destruction of the alveolar walls but without obvious fibrosis.

Table 22.1 Avoid terminological confusions1–3.

Term Includes/represents Notes
Obstructive pulmonary disorders
image Asthma
image Chronic bronchitis
image Emphysema
image Bronchiectasis
image Cystic fibrosis
 Diseases that are characterised by a reduction in expiratory airflow
COPD
image Chronic bronchitis
image Emphysema
image The term COPD is limited to these two diseases
image In some patients both diseases co-exist
Compensatory emphysema Airspace dilatation (i.e. increased inflation) in response to loss of volume elsewhere in the lung
image Very different to (COPD) emphysema
image No destruction of alveolar walls
image Example: compensatory emphysema of an upper lobe when there is total collapse of the lower lobe

CXR FINDINGS IN COPD

GENERAL

image COPD is usually suspected clinically. The diagnosis is confirmed by spirometry demonstrating airflow obstruction that is not fully reversible. The CXR has a limited role in diagnosis but can be useful:
image To exclude other causes for the patient’s symptoms.
image To assist in the management of a patient with known COPD whose clinical status shows an acute deterioration.
image Even with extensive pathological changes (COPD) or severe clinical symptoms the CXR may appear normal—particularly if the dominant disease process is chronic bronchitis.
image Caution (1): large volume lungs are not necessarily indicative of over-inflation2. They can occur in:
image healthy, well conditioned, young people
image tall people
image opera singers
image some athletes
image Caution (2): be careful about making a diagnosis of COPD on the CXR alone without supporting clinical evidence.
image

Figure 22.1 Elderly female. Severe clinical and spirometry-confirmed COPD. The CXR is entirely normal. This is the most common CXR finding.

image

Figure 22.2 Elderly male. COPD. Abnormal CXR. The domes of the diaphragm are low and flat; large bullae in both upper zones; narrow, vertical heart. (Incidental and unrelated—the right hilum is pulled upwards and laterally by scarring from a previous infection involving the upper lobe.)

CHRONIC BRONCHITIS

image The diagnosis of chronic bronchitis is made clinically on the basis of well-defined and internationally accepted features. The CXR appearance may be normal or there may be abnormalities which are very subtle or non-specific (Table 22.2).
image The principle role of the CXR is in helping to exclude diseases that can clinically mimic chronic bronchitis2. These include tuberculosis, carcinoma, bronchiectasis and lung abscess.

Table 22.2 CXR features in chronic bronchitis.

Symptoms CXR
Mild to moderate Normal
Severe
image In most patients the CXR remains normal
image A few patients show non-specific findings:
image Over-inflation—generalised
image Thickened bronchial walls:
– peribronchial cuffing (Fig. 22.3)
– parallel tubular shadows
image Areas of oligaemia (i.e. decrease in width of visible pulmonary vessels indicating reduced blood flow)
image Saber sheath (UK: sabre sheath) trachea4
image

Figure 22.3 The anatomical changes that explain peribronchial cuffing which is very occasionally seen in some patients with chronic bronchitis. The cuffing appearance is due to thickened bronchial walls seen en face on the CXR.

image

Figure 22.4 Chronic bronchitis. Normal CXR. This is the most common appearance.

EMPHYSEMA

image The CXR is frequently normal. In some patients the CXR appearances are very abnormal.
image A low diaphragm does not of itself indicate emphysema. Over-inflation of the lungs due to emphysema should only be assumed when a dome of the diaphragm is both low and flat (Fig. 22.5).
image

Figure 22.5 Over-inflated lungs. Low domes of the diaphragm are not necessarily abnormal. It should only be assumed to indicate COPD if the domes are both low and flat. On a PA CXR a flat dome is one in which its highest point is less than 1.5 cm above a line connecting the costophrenic and cardiophrenic angles2. On a lateral CXR a flat dome is one in which the diaphragmatic peak is less than 1.5 cm above a line joining the sternophrenic and posterior costophrenic angles2. Note the enlarged retrosternal air space—on the lateral CXR—a regular finding in COPD when over-inflation is present.

Table 22.3 CXR features in emphysema.

Disease severity CXR2–9
Mild to moderate
image May appear normal
image Areas combining hyperlucency (blackness) and fewer vessel markings
Severe
image A low, flat dome of the diaphragm is very suggestive
image Flat: highest level of a dome is less than 1.5 cm above a line drawn between the costophrenic and the cardiophrenic sulci (Fig. 22.5)
image Vascular changes (see p. 286)
image Bullae
image Saber sheath trachea
image Other signs…are subjective and unreliable

Vascular changes

Widespread emphysema may show the following abnormal appearances:

image A narrow, vertical, centrally situated heart. The explanation: over-inflation of the lungs causes the diaphragm to be low. Because the pericardium and the superior surface of the diaphragm are adherent, the heart is pulled inferiorly by the over-inflation. Consequently its transverse diameter appears narrow.
image The hilar vessels are prominent10. This is because there is less cardiac shadow overlap, or because the vessel margins at the hilum are sharply defined by the hypertransradiant over-distended adjacent air spaces, or because the pulmonary arteries are actually enlarged due to secondary pulmonary arterial hypertension.
image The vessels extending outwards into the lungs appear thinner or have a smaller diameter than is usual. This peripheral narrowing is in marked contrast to the very prominent hilar vessels. There may also be fewer vessels in affected areas (Fig. 22.6).
image

Figure 22.6 Emphysematous area in the mid zone of the right lung. Compare the fewer and narrower vessels in the affected area with the appearance of the vessels at the same site in the normal left lung.

Bullae

image A bulla is a thin-walled air-filled structure measuring more than 1 cm in diameter. It represents a distended pulmonary lobule or group of lobules. Sometimes bullae are very large (5–20 cm in diameter) and are the result of groups of disrupted alveoli coalescing.
image Don’t be surprised if a bulla disappears. This does happen—either spontaneously or following infection.
image

Figure 22.7 COPD. Severe emphysema. Low, flat diaphragm. Large main pulmonary arteries resulting from pulmonary arterial hypertension.

Saber sheath trachea (UK: sabre sheath trachea)

When a saber sheath appearance is present it is a reliable and sensitive sign of COPD. A saber sheath configuration is evident when the intrathoracic coronal diameter of the trachea is two-thirds of the saggital diameter or less, when measured 1 cm above the superior aspect of the aortic arch4. The precise mechanism causing this tracheal appearance remains speculative. This sign may appear in chronic bronchitis or emphysema (Figs 22.9 and 22.10).

image

Figure 22.9 Saber sheath trachea in COPD. The narrowing is limited to the intrathoracic part of the trachea. A saber sheath appearance exists when the coronal diameter of the trachea is two thirds of the sagittal diameter or less…measured 1 cm above the aortic arch4. Precise assessment requires a lateral as well as a PA CXR. Nevertheless, the tracheal narrowing is usually evident on the frontal CXR.

image

Figure 22.10 Saber sheath trachea in COPD.

image

Figure 22.8 Emphysematous bullae. Multiple ring-like shadows in all zones of both lungs. The CT confirms the presence of bullae.

KNOWN COPD: INDICATIONS FOR A CXR

A CXR is only occasionally necessary during an acute exacerbation (Table 22.4).

Table 22.4 Indications for a CXR.

image
image

Figure 22.11 COPD. Unexpected clinical deterioration. A pneumo-thorax is present. The visceral pleura (arrow) is visible.

image

Figure 22.12 COPD. Acute exacerbation with confusing clinical features. The CXR reveals an extensive pneumonia in the left mid zone. (NB: this is the same patient as shown in Fig. 22.2)

FACTS AND FIGURES

image The differential diagnosis in a patient with clinical symptoms suggesting COPD will include asthma, bronchiectasis, cystic fibrosis, left heart failure, interstitial lung disease, and upper airway obstruction.
image Chronic bronchitis. The pathological changes: mucous gland enlargement, inflammation, and bronchial wall thickening. Airflow limitation results from the deformity of the bronchial walls and narrowing of the lumina.
image Recognised causes of emphysema are: cigarette smoking, alpha 1-antitrypsin deficiency, intravenous drug abuse (cocaine, heroin, methadone), immune deficiency syndromes (including HIV infection).
image Emphysema. Autopsy studies have shown that emphysema can involve as much as 30% of the lung tissue, and yet an individual may not have had any respiratory symptoms during life5.

REFERENCES

1. American Thoracic Society. Standards for the diagnosis and care of patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 1995;152:77-121.

2. Takasugi JE, Godwin JD. Radiology of chronic obstructive pulmonary disease. Radiol Clin North Am. 1998;36:29-55.

3. Devereux G. ABC of chronic obstructive pulmonary disease. Definition, epidemiology, and risk factors. BMJ. 2006;332:1142-1144.

4. Greene R. “Saber-sheath” trachea: relation to chronic obstructive pulmonary disease. AJR. 1978;130:441-445.

5. Pratt PC. Role of conventional chest radiography in diagnosis and exclusion of emphysema. Am J Med. 1987;82:998-1006.

6. Thurlbeck WM, Muller NL. Emphysema: definition, imaging and quantification. AJR. 1994;163:1017-1025.

7. Collins J, Stern EJ. Chest Radiology: The Essentials. Philadelphia, PA: Lippincott Williams & Wilkins, 1999;200-201.

8. Foster WL, Gimenez EI, Robidoux MA, et al. The emphysemas: radiologic–pathologic correlations. Radiographics. 1993;13:311-328.

9. Klein JS, Gamsu G, Webb WR, et al. High-resolution CT diagnosis of emphysema in symptomatic patients with normal chest radiographs and isolated low diffusing capacity. Radiology. 1992;182:817-821.

10. Simon G. Principles of Chest X-ray Diagnosis, 2nd ed. London: Butterworths, 1962.