Study Syllabus for Classification of Radiographs of Pneumoconioses
Clinical Overview
Central Role of Diagnostic Imaging
Role of CT (Part 1)
The chest radiograph remains important in detection and characterization of occupational lung disease because of its relatively low cost, relatively low radiation dose, and wide availability. However, the chest radiograph is relatively insensitive to early interstitial abnormality, and imprecise for evaluation and characterization of parenchymal and pleural disease. For these reasons, there is increasing interest in the use of CT in the diagnosis of occupational lung diseases, particularly in specific contexts as delineated below. Optimal HRCT technique to detect occupational lung disease includes contiguous or noncontiguous thin sections (1.5 mm or less), acquired during suspended deep inspiration, with high resolution reconstruction [Mayo 2009]. Coronal and sagittal reconstructions from volumetric acquisitions are frequently useful, as shown in several illustrations in this section. Prone images are often helpful to identify early fibrosis in the posterior lungs, and expiratory images are helpful to identify air trapping (Fig. 13).
Detection of Early Pneumoconiosis
HRCT is generally more sensitive than chest radiographs for detecting early dust diseases of all types, particularly in workers with normal or 0/1 profusion chest radiographs [Bergin et al. 1986; Akira et al. 1986; Huuskonen et al. 2001; Staples et al. 1989]. In subjects with asbestos exposure who have chest radiograph profusion scores of 0/1 or 1/0, the presence of fibrosis on HRCT (Fig. 11) has been shown to identify subjects with abnormal physiology and bronchoalveolar lavage findings suggestive of asbestosis, while those with normal HRCT generally have normal physiology and bronchoalveolar lavage [Harkin et al. 1996]. Conversely, chest radiographs may be false positive and HRCT may fail to confirm pneumoconiosis, indicating that there may be false positive chest radiographs [Remy-Jardin et al. 1990]. (Fig. 18; note pleural thickening at left base on chest radiograph (white arrow); CT image showing pleural plaque (black arrows) not visible on the chest radiograph, while apparent pleural plaque at the left base on chest radiograph is shown to represent subpleural fat (white arrow)). Additionally, HRCT has been found to be more sensitive for detection of coalescent and conglomerate opacities compared to radiographs [Remy-Jardin et al. 1990] (Fig. 5). HRCT is also superior to chest radiograph in the detection of emphysema and other airway effects of dust exposure [Kinsella et al. 1990] (Fig. 3).
Detection of Pleural Disease
For asbestos-related pleural disease, several papers have demonstrated that CT is more sensitive and more specific than chest radiograph [Gevenois et al. 1998; Aberle et al. 1988a, 1988b] (Fig. 18). In particular, CT can identify non-calcified en-face pleural plaques, and readily distinguishes pleural plaque from extrapleural fat, a frequent cause of overdiagnosis of pleural disease on the chest radiograph [Ameille et al. 1993]. (Fig. 8), (Fig. 9). Additionally, CT has value in identification of subjects with round atelectasis related to diffuse pleural thickening, which is often associated with restrictive physiology and must be distinguished from malignancy [Lynch et al. 1988; McHugh and Blaquiere 1989] (Fig. 10).