Teaching Case

The patient was a worker in a glass manufacturing factory with known past history of cough and shortness of breath due to exposure to silica. She presented with shortness of breath which had increased during the past 15 days. No personal history of any alcohol consumption or cigarette smoking.

CE-CT scan study of chest reveals presence of large symmetric bilateral opacities with irregular margins in right upper and middle lobe and left upper and middle lobe. These show presence of linear streaks originating from hila with presence of areas of calcification. Features are suggestive of progressive massive fibrosis.

The remaining lung shows ground glass opacities, interstitial thickening and cystic areas. There is volume loss in bilateral lungs.

Mediastinum shows presence of multiple enlarged lymph nodes with egg shell calcification in the pre and paratracheal, prevascular, aortopulmonary window, subcarinal regions and bilateral hila.

Pneumoconiosis may be classified on the clinicopathological basis as fibrotic (focal or diffuse) or nonfibrotic (minimal or no fibrosis). [1] The regional differences in lymphatic flow (gravity dependent, left side inclination of main pulmonary trunk, chest wall motion milking) result in poor clearance of particles from the posterior part of the right upper lung zone. This superoposterior predilection of dust retention has been described in CT studies. [2]

The radiographic and HRCT findings of silicosis and coal worker pneumoconiosis are similar to a large extent. The findings are well circumscribed nodules, often bilateral, small (usually 2-5 mm in diameter but with a range of about 1- 10 mm), involving mainly upper and posterior lung zones migrating towards the hilum. Small nodules indicate uncomplicated disease and large (i.e. > 1 cm) nodules indicate complicated disease such as progressive massive fibrosis (PMF).

Two clinical forms of the disease are seen - Acute and classic, with acute presenting as alveolar silicoproteinosis and classic as interstitial reticulonodular. Acute typically presents as pulmonary alveolar proteinosis as far as imaging is considered, as diffuse ground glass opacities (GGO) in the perihilar region with air bronchogram on plain chest radiograph. [3]

Bilateral centrilobular nodule with GGO, multifocal and patchy in appearance with consolidation indicates that intraalveolar collection of proteinaceous content has already taken place. [4] Sometimes interlobular septal thickening caused by fibrous tissue is seen. Tuberculosis and infection with atypical mycobacteria are frequent complications. [5] The simple form of classical silicosis on chest radiographs appears as well-defined multiple nodular opacities, varying from 1-10 mm in diameter. On CT, the most characteristic feature of simple silicosis is the presence of several small nodules of 2-5 mm in diameter, accompanied by calcification. [6]

Nodules in the complicated form of classic silicosis, also known as progressive massive fibrosis (PMF) are conglomerated large nodules with multiple foci of central hyalinised collagen. Opacities are large due to accumulation of nodules commonly in the middle zone and the most favourite location being the upper lobe. At thin-section CT, nodules are usually observed in centrilobular, paraseptal, and subpleural regions and have a perilymphatic distribution. [6]

Teaching Points: 1. The radiographic and HRCT appearances of these diseases may not be distinguishable from each other and may be similar to sarcoidosis. 2. Observing coinfection with tuberculosis is to be kept in mind while reporting.