PathologyDiffuse pulmonary fibrosis
Pulmonary fibrosis is seen in the course of a number of lung diseases as shown in the following table:
Causes of diffuse pulmonary fibrosis
Tuberculosis
Fibrosing alveolitis
Pneumonoconioses
Chronic pulmonary disease
Asbestosis
Organic/inorganic disease
Silicosis
Chronic infections
Sarcoidosis
Diseases such as asbestosis, silicosis, and sarcoidosis all lead to the development of pulmonary fibrosis.
Fibrosing alveolitis
This is a group of diseases characterized by an inflammatory reaction in the endothelial cells in the alveoli with an alveolar exudate. As the disease progresses, there is destruction of the alveolar architecture. The disease is also called Hamman-Rich disease. Fibrosing alveolitis may be seen at the same time in systemic diseases such as rheumatoid arthritis, disseminated lupus erythematosus, ulcerous colitis, and chronic hepatitis. The disease is characterized by rapid progression, with only mild non-specific blurring of the affected lung segment in the early stages, followed by an increasingly diffuse outline of the pulmonary arteries, and gradual development of fine reticulonodular opacities in the basal lung segments (Fig. 74). Gradually, as the fibrosis develops rapidly, there is reduced volume of the affected lung segment. The reticular opacities become steadily coarser and gradually appear as annular shadows with diameters from 5 to 10 mm. The annular shadows represent cystic cavities in the lungs, giving these a typical honeycomb appearance. This is best
 Figure 74.
Fibrosing alveolitis with reticular opacities in both lungs.
|
seen in lateral views of the lungs, most often basally and posteriorly.
Pneumoconioses
The common characteristic of this group of diseases - of which asbestosis and silicosis are the most important - is that they are caused by organic dust particles that are small enough to reach the alveoli where a type III Arthus tissue re action takes place. Four to six hours after exposure, hypersensitivity pneumonia develops. Initially, the chest radiograph is normal. Later, diffuse blurring of the basal lung segments develop. The involved parts of the lungs have reduced circulation because of obliteration of small pulmonary vessels. After temporary exposure to dust particles, the condition returns to normal, both clinically and radiologically. However, residual changes may be seen as reticulonodular opacities 1-3 mm in diameter.
With continuing exposure to dust, pulmonary fibrosis gradually develops, characterized by coarse linear striped opacities, specially in the middle and upper part of the lungs. Considerable volume loss is seen at a late stage in the development of fibrosis. In pulmonary fibrosis caused by pneumoconiosis, small round shadows, 5-8 mm in diameter with a central translucency are seen, giving a honeycomb appearance. This special fibrosis is most typically seen in the upper lobes, unlike fibrosing alveolitis where the fibrosis is most pronounced in the basal lung segments.
The first visible radiological changes in asbestosis are small irregular opacities, mainly in the basal parts of the lungs. The middle and upper
 Figure 75.
Asbestosis - irregular striped opacities, most pronounced in the basal lung segments.
|
parts are involved at a later stage. In the earliest stages, the opacities are thread-like and are often confused with vascular shadows that branch into fine thread-like structures (Fig. 75). As the disease progresses, the linear opacities become coarser and broader, and may obscure the pulmonary arteries that branch out to the involved area. In severe cases, there are diffuse coarse reticulonodular opacities, which gradually become honeycomb-like. These opacities may be so large that they completely obscure the outline of arteries in the area, and also obliterate the outline of adjacent parts of the diaphragm and heart.
Typical changes in asbestosis are pleural involvement as plateau-chaped pleural thickening. This is typically seen in the parietal pleura, while the visceral pleura is not involved. Pleural changes are seldom observed unless the disease has lasted for at least ten years. In the frontal view, the pleural thickening is observed where the pleura is in contact with the ribs, most often in the middle third of the chest wall. The typical disk-shaped thickening of the pleura is usually called a pleural plaque. The upper and basal parts of the pleura are not affected until the more advanced stages of the disease. A pleural plaque is best shown on chest films taken tangentially.
The standard examination when asbestosis is suspected includes oblique views of the lungs with the patient rotated 45 degrees (Fig. 76). In the late stages of the disease (usually after more than twenty years), there is fairly extensive calcification in the pleural plaques. The disease is gradually dominated by extensive fibrosis with marked shrinking and considerable pleural thickening containing calcification. Calcification is
 Figure 76.
Asbestosis - oblique view (45o anteroposterior) .
|
Figure 77.
Asbestosis -linear opacities in the basal lung segments, which obliterate the outline of the pulmonary arteries peripherally.
|
most often observed in the parietal pleural on the domes of the diaphragm (Fig. 77).
Pleural fluid is unusual in asbestosis. If pleural fluid is seen, it is a strong indication of the development of malignant mesothelioma. In such cases, the pleural fluid contains blood. A chest radiograph is usually not sufficient to clarify the degree of spread of the malignant mesothelioma. This evaluation is best done by CT scan, which shows the extent of the pleural changes. By examining in the supine and prone positions, possibly also in lateral decubitus, it is easy to differentiate between pleural
 Figure 78.
Acute silicosis, alveolar infiltrate right upper lobe with air bronchogram. |
fluid and pleural thickening. Invasion into and destruction of ribs is common with advanced mesothelioma, as are metastases to the lungs and mediastinum. Distant metastases are also frequently seen.
A needle biopsy of the pleural thickening or tumor mass, under guidance of CT, gives the diagnosis, as does cytological examination of the hemorrhagic pleural fluid. In addition to the risk of developing malignant mesothelioma, patients with asbestosis also show a higher incidence of lung cancer.
Silicosis
Silicosis was previously a common disease in miners, and is due to inhalation of silicate crystals (silicon dioxide) into the alveoli. Inhaled silicate crystals develop small nodes of collagenous hyaline material. These nodes are visible on the frontal film. The lymph nodes in the hilum of the lung are usually enlarged. Eggshell-like calcification in the periphery of these lymph nodes is typical of silicosis. Although corresponding calcification may be seen in sarcoidosis, histoplasmosis, scleroderma and amyloidosis, it is rarer than in silicosis.
Infiltration of plasma cells and Iymphocytes is seen in the alveolar walls. The typical picture in acute silicosis is thus dominated by an alveolar infiltrate with air bronchogram (Fig. 78). The alveolar infiltrate may appear as small nodules. If chronic changes develop, these typical nodules disappear and the involved areas appear more like consolidated infiltrates with fibrosis (Fig. 79).
Patients with silicosis have an increased incidence of pulmonary tuberculosis.
 Figure 79.
Silicosis, consolidated infiltrates with development of fibrosis in both lungs, most pronounced in right upper lobe.
|
Sarcoidosis is a disease of unknown etiology, characterized by diffuse, non-caseating granulomas. Granulomas are typical of sarcoidosis, but may also be seen in other diseases such as tuberculosis, diverse fungal infections, and in patients with carcinoma and lymphoma. The development of sarcoidosis is probably determined immunologically by an interaction between an unidentified antigen and the organism. Sarcoidosis is sometimes associated with erythema nodosum. Although sarcoidosis is most frequent in the lung and mediastinum, the disease is also encountered in other organs such as skin, peripheral lymph nodes, spleen and the central nervous system. The diagnosis is usually made definitively by a lymph node biopsy.
The radiological picture is characterized by:
1. lymphadenopathy, and
2. parenchymal opacities
Lymphadenopathy is the most common, and is always seen in the early stages. A typical finding consists of enlarged lymph nodes in both hilar regions (Fig. 80 a, b). The lymph node enlargement is usually symmetrical and may be considerable. Lymph nodes in the mediastinum are also frequently affected, so that the radiological picture is dominated by "mediastinal tumor" and bilateral hilar lymph node enlargement (Fig. 81).
Although changes in the lung parenchyma are seen histologically in all patients, lung changes visible on a chest radiograph only develop in about 2/3 of the patients. The earliest parenchymal changes appear as small, round, irregular nodes from 1-3 mm in diameter. These are usually symmetrical and evenly distributed from the base of the apex of the lung (Fig. 82). If the disease progresses, homogenous, diffusely limited opacities appear in both lungs. Air bronchogram is frequently seen in these opacities. The opacities often appear to be consolidated infiltrates, but may also be so irregular that they appear to be nodular. In rare cases, larger almost tumor-like opacities from 1-4 cm in diameter may be seen. These have poorly defined outlines, are multiple and bilateral. The poorly defined outline generally makes it simple to distinguish these opacities from metastases, which usually have clearly defined outlines.
In 2/3 of all patients with sarcoidosis, the radiological changes improve with adequate treatment with steroids. If the disease progresses, extensive pulmonary fibrosis with marked volume reduction (shrinking) occurs. A fairly typical frontal film shows considerable upward retraction of the hilar outlines bilaterally. At the same time as the fibrosis, large emphysematous areas develop.
It is not possible to differentiate the fibrosis that develops in connection with sarcoidosis from other types of pulmonary fibrosis. Pleural thickening with pleural fluid may be seen in sarcoidosis, but is not usual.
Alf Kolbenstvedt, Arnulf Skjennald and Charles B. Higgins