Silicosis

*Silicosis* / *Chalicosis*

For medical students2 min readUpdated 2026-10-10

Silicosis is the most common and severe form of pneumoconiosis. The disease results from prolonged inhalation of dust containing free silicon dioxide and is characterized by diffuse bilateral lung damage with the development of fibrosis.

InvolvementDiffuse bilateral damage to the pulmonary parenchyma

EtiologyProlonged inhalation of dust containing free silicon dioxide

Risk GroupsMiners, sandblasters, stonemasons, foundry workers

Normal Silicon0.04–0.73% of the dry weight of lung tissue

Silicon in Disease4.7–12.35% of the dry weight of lung tissue

Etiology and Epidemiology

The term comes from the Latin word silicium (silicon). The literature also uses the synonym chalicosis, derived from the Greek chalix (lime, pebble).

Silicosis is a classic occupational disease. The primary risk groups include workers in mining, foundry, metalworking, and ceramic industries. The diagnosis is most frequently confirmed in coal mine tunnellers, stonemasons, and sandblasters.

The pathological anatomy of the disease is not limited to the pulmonary parenchyma alone. Pronounced changes affect the upper respiratory tract, bronchial tree, pleura, as well as regional lymph nodes and pulmonary blood vessels. An important diagnostic criterion is the chemical analysis of the tissues: whereas in healthy lungs the silicon dioxide content in the dry residue is only 0.04–0.73%, in silicosis this figure increases dozens of times, reaching 4.7–12.35%.

Nodular Form of Silicosis

This morphological variant develops with prolonged exposure to dust with a high content of free silicon dioxide.

Changes in the parenchyma: A significant number of specific silicotic nodules and nodes form within the lung tissue. Their sizes range from microscopic (miliary) to quite large. The shape of these formations is usually round, oval, or irregular, and on cut section, they have a characteristic gray or gray-black color.
Pleural changes: The pleural leaves are frequently involved in the pathological process. Marked thickening, induration (fibrosis), and the formation of connective tissue adhesions are observed.
Disease progression: In severe cases, silicotic nodules begin to coalesce. As a result, massive dense nodes are formed that can occupy a major part of a lobe or even an entire lung lobe. This advanced variant is termed the tumorous form of silicosis.

Diffuse-Sclerotic (Interstitial) Form

This form of pneumoconiosis is observed in patients who inhaled dust with a low content of free silicon dioxide.

Unlike the nodular type, silicotic nodules are practically absent in the pulmonary parenchyma or are present in very small numbers. However, they are frequently found outside the lungs proper—in the tracheobronchial and bifurcation lymph nodes.

The morphological picture is dominated by the proliferation of connective tissue in the form of numerous fine strands.

Dynamics of sclerosis development:

Initially, fibrotic changes are most prominent around bronchi and blood vessels (forming peribronchial and perivascular sclerosis).
Subsequently, the pathological process steadily spreads, damaging the alveolar septa.

The interstitial form is accompanied by a number of severe secondary alterations. These include generalized pulmonary emphysema, gross deformation of the bronchial tree, and the formation of bronchiectasis—areas of pathological narrowing and widening of the bronchial lumen.

Mnemonic

To easily remember the two main forms of silicosis, link them to the dust's silicon concentration. High silicon means rolling dense "snowballs" (forming the nodular form with large nodes). Low silicon means pulling fine "threads" (developing the diffuse-sclerotic form with connective tissue strands).

Frequently asked questions

What microscopic stages of silicotic nodule formation are distinguished?

Four sequential stages of silicotic nodule formation are distinguished.

Phagocytosis — alveolar macrophages engulf dust particles and transform into coniophages.
Accumulation — clearance of dust-laden cells slows down, forming accumulations in alveolar spaces and ducts.
Cellular-fibrous nodule stage — collagen fibers appear between the cells.
Fibrous nodule stage — dust cells gradually undergo apoptosis/necrosis, collagen content increases, forming a typical fibrous nodule.

What specific complications are characteristic of silicosis?

Silicosis is characterized by the development of several pulmonary and cardiovascular complications.

Cor pulmonale — develops secondary to diffuse sclerotic processes and pulmonary hypertension.
Inflammatory processes — include pleuritis, interstitial pneumonia, and bronchopneumonia.
Pulmonary emphysema — tends to be generalized.
Spontaneous pneumothorax — occurs rarely due to prominent adhesions in the pleural cavity.
Bronchial changes — deformation, narrowing, and dilatation with the formation of bronchiectasis.

What is the cellular pathogenesis of silicotic nodule formation?

The leading link in the cellular pathogenesis of silicotic fibrosis is the death of coniophages via autolysis.

Phagocytosis — macrophages engulf quartz particles.
Membrane damage — quartz particles disrupt phagolysosomal membrane permeability.
Enzyme release — hydrolytic enzymes leak from phagolysosomes into the cytoplasm.
Cell death — autolysis and death of macrophages occur.
Biochemical changes — underoxidized compounds, including lactic acid, accumulate in the lung tissue.
Fibrosis — coniophage death and metabolite accumulation stimulate fibroblasts, activating collagen synthesis.

What silicon dioxide content in lung tissue is considered normal versus indicative of silicosis?

Normally, in a healthy individual, the proportion of silicon dioxide in the dry weight of lung tissue ranges from 0.04 to 0.73%. With the development of silicosis, massive dust accumulation occurs, and this indicator sharply rises, reaching values of 4.7 to 12.35%.

What is the tumorous form of silicosis and when does it occur?

The tumorous form is a variant of severe progressive nodular silicosis. It occurs when multiple silicotic nodules coalesce into giant unified nodes capable of occupying a major portion of a lobe or an entire lung lobe.

Where are silicotic nodules most commonly localized in the diffuse-sclerotic form of the disease?

In the diffuse-sclerotic (interstitial) variant, nodules are virtually absent in the lung tissue itself. However, they are frequently found in regional bifurcation lymph nodes.

Go deeper

Pathomorphological changes in bifurcation lymph nodes in pneumoconioses.
Mechanisms of bronchiectasis formation and bronchial deformation in interstitial sclerosis.
Histological picture of pleural fibrosis (hematoxylin and eosin staining).
Features of peribronchial and perivascular sclerosis development in early stages.
Pathogenesis of generalized emphysema as a complication of the diffuse-sclerotic form.