Ref:Textbook of pathology (Harsh mohan) 6th edition,page no.491 MORPHOLOGIC FEATURES. Grossly, the chronic silicotic lung is studded with well-circumscribed, hard, fibrotic nodules, 1 to 5 mm in diameters. They are scattered throughout the lung parenchyma but are initially more often located in the upper zones of the lungs. These nodular lesions frequently have simultaneous deposition of coal-dust and may develop calcification. The pleura is grossly thickened and adherent to the chest wall. There may be similar fibrotic nodules on the pleura and within the regional lymph nodes. The nodular lesions are detectable as egg-shell shadows in chest X-rays. The lesions may undergo ischaemic necrosis and develop cavitation, or be complicated by tuberculosis and rheumatoid pneumoconiosis Histologically, The following features are observed 1. The silicotic nodules are located in the region of respiratory bronchioles, adjacent alveoli, pulmonary aeries, 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 fuher 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 paicles 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 fibrosis of coal-workers' pneumoconiosis (described above). 5. The intervening lung parenchyma may show hyperinflation or emphysema.. 6. Cavitation when present may be due to ischaemic necrosis in the nodules, or may reveal changes of tuberculosis or rheumatoid pneumoconiosis (Caplan's syndrome), discussed already.