Teaching Case

A 44-year-old male patient presented with complaints of breathlessness and cough with expectoration for the past 6 months. He had a history of working in a silica plant manufacturing company for the past 20 years. There was no history of fever, hemoptysis, chest pain, joint pain, skin rash, or wheeze.

High-resolution CT images of the above-mentioned patient studied on the same date showed multiple hyperdense sub-centimetric randomly arranged pulmonary nodules(Figure 1a & 1b) and conglomerate calcific nodules in bilateral upper lobes predominantly in perilymphatic location(Figure 2a & 2b). Multifocal patchy areas of ground-glass opacities were noted in the bilateral lung parenchyma(Figure 4).

Fibrosis with collapse consolidatory changes, traction bronchiectasis, and architectural distortion were noted in bilateral upper lobes(Figure 3). Multiple enlarged lymph nodes with eggshell calcifications were noted in prevascular, right upper paratracheal, and bilateral lower paratracheal, subcarinal, paraaortic, and subaortic regions, largest measuring ~1.4x1.0 cm in the paraaortic region(Figure 5). There was no evidence of pleural effusion/pericardial effusion. The Chest wall including the ribs and soft tissue were normal. Multiple sub centimetric micronodular calcifications were noted diffusely involving the splenic parenchyma with relative subcapsular sparing with few adjacent calcified peripancreatic nodes(Figure 6a & 6b).

Silicosis is caused by the inhalation of fine particles of crystalline silicon dioxide (silica)[1]. Quartz is the most common form of crystalline silica but is less fibrogenic than tridymite or cristobalite. Occupations such as mining, quarrying, and tunnelling are associated with silicosis [2]. The disease occurs in two clinical forms: acute silicosis, which manifests as alveolar silicoproteinosis; and classic silicosis, which manifests as chronic interstitial reticulonodular disease. Cases of classic silicosis may be classified as either simple or complicated, according to the radiographic findings [1]. Simple silicosis is defined by a radiographic pattern of small and round or irregular opacities, whereas complicated silicosis, or progressive massive fibrosis, is characterized by large conglomerate opacities[1].

Carcinoma and tuberculosis are potentially serious complications of silicosis[3]. The development of carcinoma or tuberculosis is a strong independent predictor of mortality in patients with silicosis[4] Pulmonary symptoms such as dyspnoea become increasingly severe as the radiologic abnormalities worsen with carcinoma or tuberculosis[5]

At CT, the most characteristic feature of simple silicosis is the presence of multiple small nodules 2–5 mm in diameter [3] accompanied by calcifications[7]. Subpleural nodules have a rounded or triangular configuration, and if they are confluent, they may resemble pleural plaques[7]

Complicated silicosis, also known as progressive massive fibrosis, develops through the expansion and confluence of individual silicotic nodules. On chest radiographs, complicated silicosis usually is indicated by large symmetric bilateral opacities with a diameter of more than 1 cm and with an irregular margin[5,6] The large opacities result from nodule coalescence and are observed commonly in the middle lung zone or peripheral one-third of the lung on axial chest images and the upper lung zone on longitudinal images. The large opacities gradually migrate toward the hilum, leaving emphysematous lung tissue between the fibrotic tissue and the pleural surface [1]. The CT features of progressive massive fibrosis are focal soft-tissue masses, often with irregular or ill-defined margins and calcifications, surrounded by areas of emphysematous change [7,8]

Splenic involvement of silicosis is rarely seen, and patients generally do not experience spleen-related symptoms. Radiologically, numerous well-circumscribed micronodular calcifications are seen in the splenic parenchyma, usually with subcapsular sparing. Although the mechanism of splenic involvement of silicosis is not fully understood, it is thought to occur with the hematogenous or lymphatic spread of silica (or both). Splenic involvement of silicosis may be accompanied by abdominal lymph nodes with eggshell calcification. Silicosis does not have a specific treatment, but removing the source of exposure is important to prevent the disease from worsening [9]

Take home message: In silicosis, even if the imaging findings are specific for lungs, radiologists should look beyond lungs to identify other organ involvement.

Written informed patient consent for publication has been obtained.