Asbestos is a naturally occurring group of magnesium silicate minerals that are made up of tiny microscopic fibers with very good insulating and heat-resistant properties. Asbestos fibers are divided into two basic groups: The serpentine fibers, having long curly fibers, which include Chrysotile, and the amphibole fibers, having straight, short, needle-like fibers, which include Crocidolite and Amosite. In general, the smaller and straighter the fiber, the deeper it can be lodged into the lungs and the more harmful it is. The amphiboles are more harmful than the serpentines. However, Chrysotile, a serpentine type fiber, was the most common asbestos product used in the United States. Asbestos fibers, when breathed into the lung, can irritate the chest wall and lung linings (the pleura) or the lung itself (the parenchyma). It can also be swallowed and can penetrate the abdominal cavity irritating it as well as abdominal organs.
Disease caused by asbestos includes irritation to the lung lining with accumulation of fluid known as a pleural effusion; scarring of the chest walls, diaphragms and mediastinum known as pleural (circumscribed) plaquing; scarring of the lung lining or fusion of the lung lining to the chest wall often occurring after a pleural effusion(s) called diffuse pleural thickening; which when associated with extension into and distortion of the lung tissue is known as cicatricial scarring; and when infolding the lung into its scar mass is called rounded atelectasis. Scarring of the lung tissue is known as interstitial or parenchymal fibrosis, which in its end stage develops honeycombing. Cancers can occur to the chest wall lining known as amesothelioma or to the lung tissue known as a lung cancer or carcinoma.
On chest radiographs, there has been an attempt by various national and international organizations to standardize readings of chest x-rays in workers having had occupational dust and fiber exposure and to classify them such that they can be compared. This has evolved into the ILO system – the International Labor Organization system of interpretation of chest radiographs. The ILO system rates the quality of the frontal chest x-ray, describes the presence or absence of disease of the lung that can be caused by occupational dust or fiber exposures, and rates lung scarring according to its size and shape, its location within the lung – upper, mid or lower lung zones, and the concentration of visualized lung scarring per unit area of the disease process, also known as the profusion. In addition, there is a discussion of the presence or absence of pleural plaquing – scarring of the lining of the chest walls, diaphragms and mediastinum or diffuse pleural thickening – scarring of the lining of the lung, as well as a description of “other findings” both presented as check boxes of specific symbols for specific findings, or as an open-ended discussion entry. The below visuals are to help you understand what these findings look like and how they are classified, both for plain radiographs, supine spiral CT and prone HRCT.