Asbestos-Induced Pleural Disease
KeywordsMalignant Mesothelioma Asbestos Exposure Pleural Disease Pleural Plaque Asbestos Body
Asbestos is a family of naturally occurring silicates which, when used in a variety of construction and manufacturing ways, provides significant heat-resistance. As such, it has historically been used for, among other things, building construction and shipbuilding. It is reported that the amphiboles amosite and crocidolite, and the serpentine fiber chrysotile, are the primary causes of asbestos-related disease.
Although asbestos has been vilified, asbestos’ unique properties and natural occurrence led to its use throughout history. It reportedly was used for lamp and candle wicks as long ago as 4000 BC, and between 3000 and 2000 BC Egyptian pharaohs were embalmed using asbestos cloth wrapping to better preserve the pharaoh. In the 1300s, Marco Polo visited an asbestos mine in China, where he identified asbestos as a stone and ended the myth that asbestos was the hair of a woolly lizard. In the 1700s, asbestos papers and boards were manufactured in Italy. From the mid-1800s, asbestos was increasingly used in the United States and other countries for manufacturing and construction purposes, and in the mid-twentieth century, wartime use and postwar construction heavily relied upon asbestos.
Pleural diseases and lung diseases are characteristic changes of asbestos exposure. Lung diseases include asbestosis and asbestos-related lung cancer, and pleural diseases include diffuse malignant mesothelioma, pleural effusion, formation of pleural plaques, and rounded atelectasis. Diagnosis is often considered based on the patient’s clinical history of asbestos exposure, as well as radiologic findings. In many cases of asbestos-related pleural disease, histologic diagnosis is necessary for an accurate diagnosis. This is important not only for the purposes of prognosis and treatment but also for medical-legal reasons. In many cases of asbestos-related pleural disease, treatment is supportive; however, with diffuse malignant mesothelioma surgery and nonsurgical therapies are often employed with the aim of improving survival. Rounded atelectasis may also be treated surgically.
Pleural diseases induced by asbestos include diffuse malignant mesothelioma, localized fibrous pleural plaques, recurrent benign pleural effusions, diffuse pleural fibrosis, and rounded atelectasis. Some of these conditions are discussed in detail elsewhere in this Encyclopedia. Localized fibrous pleural plaques, recurrent benign pleural effusions, rounded atelectasis, and diffuse pleural fibrosis are briefly discussed below.
Discrete pleural plaques may be identified in approximately half of the workers with significant asbestos exposure. Plaques typically involve parietal pleura between the fifth and ninth ribs bilaterally, as well as the diaphragm. Calcification of pleural plaques, a common feature, may radiologically mimic severe lung disease when examined by chest x-ray superimposed on the lung fields; however, CT scan typically easily differentiates lung parenchymal disease from pleural disease in these patients. Localized fibrous pleural plaques, localized pleural fibrosis that is usually located on the diaphragm or posterior inferior parietal pleura, are the most common manifestation of asbestos exposure. The finding of bilateral, superior diaphragmatic plaques with clear costophrenic angles and calcifications strongly suggests that the plaques are asbestos-related. Patients with pleural plaques are typically asymptomatic, and the plaques are usually identified incidentally. It is important to remember that pleural plaques often are merely deposits related to healed inflammatory processes, unrelated to asbestos exposure. Bilateral, symmetric plaques, however, are more likely to be related to asbestos exposure. With asbestos-related pleural plaques, the number and size of pleural plaques are unrelated to intensity or time of asbestos exposure. Radiographically and grossly, pleural plaques are generally less than 1 cm in thickness, and approximately 10% may contain foci of calcification. The plaques are grossly discrete, shiny, mildly elevated firm lesions on the pleural surface. They may contain obvious calcifications. Histologically, they comprise layers of dense acellular hyalinized collagen in a basket-weave pattern. Asbestos bodies are not histologically obvious; however, they are often demonstrable with digestion-filtration techniques.
Recurrent benign pleural effusions are rare and are diagnosed when, with the exclusion of another effusion causes disease process, there is a reliable history of asbestos exposure, radiographically or thoracentesis-confirmed pleural effusion, and the lack of the development of a pleural neoplasm after 3 years from identification of the pleural effusion. The condition arises typically at least 10 years after the first asbestos exposure. Half of these effusions are hemorrhagic and up to a quarter may be eosinophilic. Patients are generally asymptomatic; however, chest pain, dyspnea, cough, and fever may occur. Recurrent benign pleural effusions are not distinguishable radiographically from effusions due to other causes. These effusions, usually small, often resolve spontaneously in approximately 3 months; however, up to one-third may recur.
Rounded atelectasis is a benign expression of pleural thickening in which invagination of pleura into the parenchyma can entrap lung tissue causing atelectasis. On chest x-ray and CT scan, rounded atelectasis characteristically exhibits a curvilinear, scar-like lesion, often in the lower lung areas. As such, it may radiologically mimic lung cancer. Rounded atelectasis is a focal, often lower-lobe-based, pleural-based lesion that occurs due to plural scarring. Underlying lung parenchyma becomes atelectatic, which is often surgically excised because it mimics neoplasm. It is typically identified incidentally on radiology. Chest x-ray shows a wedge-shaped or rounded, well-circumscribed mass, and CT scan often shows air bronchograms, often a “comet-tail” area of curvilinear bronchovascular bundle adjacent to the mass. There is retraction and pleural scarring on gross examination with underlying atelectasis. Histologically, rounded atelectasis shows atelectatic lung parenchyma with overlying pleural fibrosis, with variable amounts of chronic inflammation. Treatment is usually surgical with good prognosis, as the lesion is not neoplastic.
Diffuse pleural fibrosis is a typically asymptomatic diffuse, bilateral condition, occurring in approximately 20% of patients with prolonged asbestos exposure, which may occur in association with asbestos-related pleural plaques. Diffuse pleural fibrosis involves both parietal and visceral pleura. In some patients, diffuse pleural thickening may cause pulmonary restriction. It is seen radiologically as a smooth pleural opacity involving at least one-fourth of the chest wall. On gross examination, it is typically based in the lower lung areas. In severe cases, it restricts the lung and binds it to the chest wall. Histologically, there is acellular to paucicellular pleural fibrosis which may mimic fibrous pleuritis or desmoplastic diffuse malignant mesothelioma. Fibrosis is often seen in a basket-weave pattern. Diffuse pleural thickening may contain calcifications. Treatment is generally supportive.
Diffuse malignant mesothelioma is a rare pleural neoplasm. Approximately 80% of diffuse malignant mesotheliomas diagnosed currently are related to prior occupational asbestos exposure that occurred up to the early 1970s. The latency period from asbestos exposure to the development of diffuse malignant mesothelioma is decades long. Because of these characteristics, the vast majority of asbestos-related diffuse malignant mesotheliomas occur in older men. Other types of mesothelioma, such as localized malignant mesothelioma and well-differentiated papillary mesothelioma, have not been shown to be related to asbestos exposure.
References and Further Reading
- Churg, A., & Green, F. H. Y. (1998). Pathology of occupational lung disease (2nd ed.). Baltimore: Williams & Wilkins.Google Scholar