Clinical History
Two women, mother(50-years-old) and daughter(30-years-old), living near an asbestos related factory, underwent chest radiographs and HRCT in the context of periodical screening, recommended by the local attendant doctor due to the high incidence of lung cancer and mesotelioma in the local population. No other prior medical problems were reported.
Imaging Findings
Mother and daughter were living for a period of about 40 and 20 years, respectively, in the proximity of an asbestos related factory. Both women were asymptomatic.
According to the information provided on the referral letter by the local attendant doctor, the chest radiographs demostrated findings of asbestosis and so a HRCT scan was ordered.
The daughter’s HRCT revealed non calcified pleural thickening along with normal imaging of the pulmonary parenchyma, whereas calcified plaques were shown in the mother’s HRCT. Lesions of pulmonary fibrosis were also present in the older woman’s imaging, such as subpleural curvilinear lines and thickening of the interlobular septa in subpleural and basal zones.
Discussion
Asbestos is the name given to a group of naturally occurring silicate minerals. It is not combustible, has great tensile strength, and has good frictional properties. These properties have led to its use in many commercial and domestic settings. Exposure to asbestos arises from mining and processing of asbestos and manufacture of asbestos products. The main asbestos-related conditions and diseases include pleural effusion, pleural plaques, diffuse pleural thickening, asbestosis, malignant mesothelioma, and bronchogenic carcinoma.
Benign pleural manifestations of asbestos exposure include circumscribed pleural plaques, round atelectasis, benign exudative effusions and diffuse pleural fibrosis. Pleural plaques, usually asymptomatic, are the most common benign manifestations of asbestos exposure. There is a latency period of 20 and 40 years. They appear on CT as discrete areas of fibrosis that usually arise from the parietal pleura but may arise from visceral pleura. Visceral pleural plaques are associated with abnormality in the adjacent lung parenchyma. Plaques are usually found postero-laterally as well as along the diaphragm. Calcifications occur in approximately 10-15% of plaques.
Asbestosis is defined as interstitial fibrosis caused by inhalation of asbestos fibers. It occurs 15 to 20 years after exposure, with disease progressing even after exposure has ceased. Initially, asbestosis affects respiratory bronchioles with development of peribronchial fibrosis. Progressively, the alveolar walls are involved and eventually the interlobular septa. The fibrosis tends to be patchy and is usually more severe in the subpleural regions of the lower lobes and posterior lungs. Clinico-laboratory findings suggesting the disease are: the restrictive lung disease on pulmonary function testing as well as a diffusion abnormality, the presence of rales at auscultation and abnormal chest radiograph (ILO score).
HRCT is more sensitive than the radiograph in the detection of asbestosis. The diagnosis of asbestosis on HRCT is based on clinical history of exposure, findings indicative bilateral pulmonary fibrosis and bilateral pleural plaques or diffuse pleural thickening. It is recommended that in patients being assessed for asbestosis, HRCT scans be obtained in both supine and prone positions because in many cases the fibrosis is mild and limited to the dependent regions of the lower lung zones.
The earliest pulmonary abnormalities, although nonspecific, consist of subpleural nodules or dotlike opacities 1mm or less in diameter. They are situated a few millimetres away from the pleura and may appear as fine branching structures. Confluence of nodules leads to pleura-based nodular irregularities and subpleural curvilinear lines. As the fibrosis progresses, intralobular lines and irregular thickening of the interlobular septa are seen on HRCT as well as parenchymal bands. With further progression, architectural distortion, traction bronchiectasis and honeycombing are seen.
The HRCT findings of asbestosis resemble those of interstitial pulmonary fibrosis (IPF). Nevertheless, in asbestosis there is great prevalence of subpleural dotlike or branching opacities, parenchymal bands, and subpleural lines as well as more-marked distribution of the disease in subpleural and basal zones. On the other hand, honeycombing and traction bonchiectasis are more prevalent in IPF. Furthermore, ground-glass opacities are relatively uncommon in asbestosis.
Differential Diagnosis List
