Pathology

Respiratory diseases and emphysema

Asthma

In bronchial asthma, radiographs of the lungs are often completely normal. There are no specific radiological findings, and the object of radiography is partly to exclude other causes of breathing difficulties such as pulmonary edema or tracheal obstruction, and partly to detect complications such as pneumothorax or atelectasis caused by mucus plugs.

Chronic bronchitis

Like asthma, chronic bronchitis is defined on the basis of the clinical picture. Half the patients with chronic bronchitis have a normal radiograph, and the changes that occur are caused by secondary conditions such as pneumonia or emphysema. Striped or mottled opacities may be due to scars after previous infections, possibly combined with fluid-filled bronchiectatic cavities. Bronchography shows irregularities in the walls and dilated openings from the mucous glands, and the bronchial tree has fewer and coarser branches than normal.

Emphysema

Unlike asthma and chronic bronchitis, emphysema is defined in strict morphological terms as a condition of the lung characterized by abnormal permanent enlargement of air spaces distal to bronchioles, accompanied by destruction of their walls without obvious fibrosis. The definition does not include any functional impairment or airway obstruction. Thus, abnormal function tests or airway obstruction are not invariably present in emphysema. Emphysema is a general pathological mechanism with a multitude of causes and appearances. Imaging features correlate well with microscopy using serial sections, less well with various functional parameters.

Classification
Emphysema may be pan-acinar with involvement of the whole acinus, or it may be localized only in the central or only in the peripheral parts of the acini (centrilobular and paraseptal emphysema).

Table 3. Classification of emphysema

Type	Clinical association
Panlobular Centrilobular Paraseptal Irregular	alpha-1 antitrypsin deficiency Smoking Spontaneous pneumothorax Paracicatrical, old adjacent scar, rarely symptomatic

a  b

Figure 42. Emphysema a) PA view b) Lateral view Scanty peripheral vascular shadows, specially basally. Low level of diaphragm domes and increased amount of retrosternal aerated lung tissue. Small heart shadow.

The chest film diagnosis of emphysema (Fig. 42) is based on:
1. Signs of hyperinflation (flat diaphragm, increased retrosternal space, bullae, large chest cage), and
2. Vascular criteria (decreased peripheral vessels, narrowed midline vessels, local avascular areas, large pulmonary arteries)

The overall diagnostic accuracy is 65-80 % depending on the clinical material studied. The false negative rates are significant. The sensitivity increases with increasing severity of emphysema in the population studied. Specificity is relatively good with few false positives. These are due

Figure 43. Child, suspected of having aspirated a foreign body. A foreign body occludes the middle lobe bronchus, causing atelectasis of the middle lobe. In addition there is a valvular mechanism in the main bronchus with hyperinflation of the right lower and upper lobes.

to misinterpretation of normal variation of vascularity, abnormalities of the thoracic cage, asymmetry of thoracic soft tissues (mastectomy, muscular atrophy), or overexposed radiographs,

Emphysematous conditions may be associated with obstruction of airways (air trapping), e.g. in chronic bronchitis, foreign body (Fig. 43), or congenital lobar emphysema. Emphysema without obstruction occurs with pure destruction of lung tissue (for example centrilobular emphysema) or with compensatory emphysema, when, for example, a lobe of the lung expands into the available space in the chest cavity after a lobectomy. Hyperinflation is a better term for air space expansions without tissue destruction.

In about a third of the patients with extensive emphysema, aerated thin-walled cavities or bullae are found. These may vary from less than one to several centimetres in diameter, and sometimes expand to the extent that one or a few bullae can occupy most of the chest cavity and compress the remaining, healthy lung tissue (Fig. 44).
The cause of unilateral emphysema (MacLeod's syndrome) is not known. It is postulated that the condition is caused by an infective condition in childhood with involvement of small bronchi and bronchioles, resulting in obstruction and dilatation of the peripheral air spaces. The effected lung has a small artery, and both the arteries and bronchial tree have fewer branches than normal. The lung is more radiolucent than the contralateral lung and retains its volume during expiration.

Figure 44. CT picture of patient with emphysema. Large, air-filled bullae. Note that only the narrow "anterior junction line" separates the two lungs at the front.

Another cause of unilateral emphysema is unilateral lung transplantation in the treatment of emphysema. The remaining emphysematous lung will push the mediastinum towards the transplanted lung.

With obstruction of a lobar bronchus in the newborn period, congenital lobar emphysema may occur that only involves one lobe. It is important not to confuse this type of condition with compensatory emphysema due to atelectatis of the adjacent lobe of the lung.
Computed tomography (particularly high resolution CT) has proved useful in the diagnosis of emphysema. The grading of emphysema is done by:
- quantitative analysis, or
- visual grading
Quantitative analysis is based on density measurements with a variety of density or pixel indices. With visual grading, emphasis is on non-peripheral, unmarginated low attenuation areas.

CT is superior to conventional radiography in detection, grading, and characterization of emphysema and the inter-observer agreement is also better. CT is useful in the detection of bullae and in the evaluation of indications for bullectomy.

Bronchiectasis

In healthy individuals, the bronchial tree has smooth walls and the calibre of the branches gradually decreases towards the periphery. In bronchiectasis, an irreversible dilatation of the bronchial branches occurs. This may be due to congenital or acquired weakness of the wall due to infection with shrinking and pulling on the wall, or to chronic

Figure 45. Different types of bronchiectasis. 1. normal bronchial tree; 2. cystic bronchiectasis 3. cylindrical bronchiectasis; 4. multiple successive dilatations ("varicose" bronchiectasis)
	Figure 46. Annular opacities at the base of the upper and lower lobes due to bronchiectasis.

obstruction. There is often a combination of causes. Cylindrical bronchiectasis is present when a bronchial branch retains its calibre without narrowing peripherally. Other types include cystic bronchiectasis, which has an appearance mimicking bunches of grapes, or there may be multiple successive dilatations of a bronchial branch (Fig. 45).

Standard radiographs may be normal. In some individuals, the dilated areas are displayed as round translucencies (Fig. 46). When these contain some dependent fluid, the diagnosis is easier as the fluid assumes a crescent shape with upward concavity. When the dilated bronchi are full of fluid or pus, they appear as oblong opacities, most often in a lobe with a reduced volume.

Figure 47. CT section of patient with pronounced bilateral bronchiectasis.

Bronchography has been a common supplementary examination when bronchiectasis is suspected, and also to clarify the extent of disease before possible lobectomy. High resolution CT can demonstrate bronchiectasis (Fig. 47), and the need for bronchography is therefore diminishing.

Atelectasis

This is a term that is used to describe volume-reduced, collapsed nonaerated lung tissue. Atelectasis is a condition that can be congenital or acquired, and the atelectatic areas may be limited to small parts of a segment, or there may be collapse of a whole lo be or lung.

Atelectasis may be caused by obstruction of a bronchus, or external compression of the lung tissue.

Table 4. Causes of bronchial obstruction

- foreign body - bronchial cancer - benign intrabronchial tumor - mucus plug - incorrectly placed bronchial tube - stenosis after infection - compression of a bronchus from the outside (tumor, lymph node)

Figure 48. Drawing of changes due to atelectasis of upper and lower lobes.

 

Table 5. Causes of compression of lung tissue

- fluid in the pleural cavity - air in the pleural cavity - elevated diaphragm - deformity of the chest wall - deliberate compression by surgery (thoracoplasty, oil in the chest cavity)

Table 6. Radiological fin dings with lobar or segmental collapse

- the collapsed segment of the lung appears itself as an opacity - the outlines of the mediastinum, heart or diaphragm, are obliterated because of absence of adjacent aerated lung tissue - change in position of neighbouring structures such as the mediastinum, - diaphragm, or lobe of lung in order to compensate for the volume reduction

When there is collapse of the upper lobes, the lateral films will show the posterior limit of the collapsed lobe distinctly. In the frontal picture, the superior mediastinal outline will be obliterated (Fig. 48). On the left side, parts of the cardiac margin will also be obliterated because the lingular lobe is part of the left upper lobe. The lateral outline of the collapsed right upper lobe is normally distinct, because the x-ray beam is tangential to the superiorly displaced border to the middle lobe. The lateral border of

a  b

Figure 49. Atelectasis of the right lower lobe in patient with metastases from rectal carcinoma. a) The PA view shows atelectasis of the lower lobe (A), as a sharply defined triangular opacity. A large metastasis is seen below the right hilum, and several small metastases (arrows). b) Lateral view. No sharply defined opacity, but increased density over basal parts of the thoracic column, which normally becomes darker caudally. Obliterated posterior part of the left dome of the diaphragm (arrows).

a collapsed left upper lobe is usually indistinct, and the opacity has a completely gradual transition to normal aerated tissue in the hyperinflated left lower lobe.

Collapsed lower lobes will generally have a distinct border in the frontal film. The collapsed left lobe may be hidden behind the heart shadow, and only observed as a retrocardiac triangular opacity on well penetrated films. In the lateral projection, the collapsed lower lobes do not have a distinct anterior border, but they are discovered because the thoracic column, which appears progressively darker towards the diaphragm, appears lighter because of the adjacent collapsed lobe (Fig. 49 a + b, 50 a + b). The dome of the diaphragm is obliterated where there is absence of normal aerated adjacent lung tissue (Fig. 48).

An atelectatic middle lobe is seen distinctly in the lateral film as a narrow triangular opacity with the tip towards the hilum. In the frontal film, the right heart outline is obliterated. Rapid treatment of the middle lobe

a  b

Figure 50. Atelectasis of the lower lobe. a) PA view. Indistinct opacity behind the heart shadow (arrows), with obliteration of medial part of left diaphragmatic outline. Clearly visible thoracic column because the heart and mediastinum are pulled across to the left. b) Lateral view. No sharply defined opacity, but gradually increasing opacity caudally down the vertebral column, and obliteration of the left diaphragmatic outline.

atelectasis with adequate physiotherapy is important because re-expansion may be difficult. Deficient re-expansion may lead to middle lobe fibrosis.

In total collapse, the volume of the lower lobe may be so small that it may be difficult to recognize. There will be considerable compensatory hyperinflation of the upper lobe, which can be misinterpreted as a unilateral emphysematous lung. Careful inspection will usually reveal an area of obliterated diaphragmatic outline, and the collapsed lobe can easily be demonstrated by CT scan.

Deficient re-expansion of lung tissue after pneumonia or embolism with bleeding may lead to persistent linear opacities, which often occur in the base of the lungs as 3-5 cm long bands, and represent platelike atelectasis.

In the presence of pleural fluid, the tongue of lung tissue that normally projects into the posterior costophrenic angle may float upward and be folded behind the lung. Adhesion may occur between the folded up part and the posterior surface of the lung. When the fluid is resorbed, the folded part may not re-expand because of the adhesions. It then lies as a round opacity towards the posterior pleura, while the other parts of the lower lobe expand into the costophrenic angle. This type of opacity has a characteristic appearance and is called round atelectasis.

 

Alf Kolbenstvedt, Arnulf Skjennald and Charles B. Higgins