Page 507 - Textbook of Pathology, 6th Edition

1. The silicotic nodules are located in the region of 491
respiratory bronchioles, adjacent alveoli, pulmonary
arteries, in the pleura and the regional lymph nodes.
2. The silicotic nodules consist of central hyalinised
material with scanty cellularity and some amount of dust.
The hyalinised centre is surrounded by concentric
laminations of collagen which is further enclosed by more
cellular connective tissue, dust-filled macrophages and a
few lymphocytes and plasma cells. Some of these nodules
may have calcium deposits.
3. The collagenous nodules have cleft-like spaces
between the lamellae of collagen which when examined
polariscopically may demonstrate numerous birefringent
particles of silica.
4. The severe and progressive form of the disease may
result in coalescence of adjacent nodules and cause
complicated silicosis similar to progressive massive
Figure 17.29 Gross appearance of the lung in silicosis, diagram- fibrosis of coal-workers’ pneumoconiosis (described
matic appearance. above).
5. The intervening lung parenchyma may show
MORPHOLOGIC FEATURES. Grossly, the chronic silico- hyperinflation or emphysema.
tic lung is studded with well-circumscribed, hard, fibrotic 6. Cavitation when present may be due to ischaemic
nodules, 1 to 5 mm in diameters. They are scattered necrosis in the nodules, or may reveal changes of tuber-
throughout the lung parenchyma but are initially more culosis or rheumatoid pneumoconiosis (Caplan’s
often located in the upper zones of the lungs. These syndrome), discussed already. CHAPTER 17
nodular lesions frequently have simultaneous deposition
of coal-dust and may develop calcification. The pleura is CLINICAL FEATURES. The functional effects of silicosis
grossly thickened and adherent to the chest wall. There develop slowly and insidiously. The main presenting
may be similar fibrotic nodules on the pleura and within complaint is dyspnoea. In time, the patient may develop
the regional lymph nodes. The nodular lesions are features of obstructive or restrictive pattern of disease. Other
detectable as egg-shell shadows in chest X-rays. The complications such as pulmonary tuberculosis, rheumatoid
lesions may undergo ischaemic necrosis and develop arthritis (Caplan’s syndrome) and cor pulmonale may occur.
cavitation, or be complicated by tuberculosis and The chest radiograph initially shows fine nodularity, while
rheumatoid pneumoconiosis (Fig. 17.29). later there are larger and coalescent nodules. Silicosis does
Histologically, the following features are observed not carry increased risk of developing bronchogenic
(Fig. 17.30): carcinoma. The Respiratory System

Figure 17.30 Microscopic picture of the lung in silicosis. The silicotic nodule consists of hyaline centre surrounded by concentric layers of
collagen which are further enclosed by fibroblasts and dust-laden macrophages. Polarising microscopy in photomicrograph on right shows bright
fibres of silica.