What is Pleural Thickening
Diffuse pleural thickening is one of two non-malignant diseases which affect the pleura of the lung.
The other non-malignant pleural disease is pleural plaques. Diffuse pleural thickening refers to widespread pleural thickening and usually affects the visceral pleura. Focal pleural thickening is a term which can be used to describe a single area of pleural thickening, often referred to as pleural plaque. This section contains information in relation to diffuse pleural thickening. For information in relation to focal pleural thickening/pleural plaque.
The pleural membrane is the protective tissue between the outside of the lungs and the inside of the chest cavity which is thin, moist and slippery. The pleural membrane consists of two layers; and the inner layer (or visceral pleura) covers the lungs and the outer layer (or parietal pleura) lines the inner aspect of the chest cavity. The pleura are covered with a layer of mesothelial cells. The space between the two layers normally contains fluid which lubricates and enables the movement of the lung during respiration.
Pleural thickening occurs as a result of scarring, calcification and/or thickening of the pleura. Diffuse pleural thickening consists of a layer of confluent pleural thickening.
Diffuse pleural thickening can be either bilateral (meaning that it affects both lungs) or unilateral (affecting only one of the lungs).
What causes pleural thickening?
While exposure to asbestos is often the cause of pleural thickening there are many other known causes of pleural thickening which include:-
- Bacterial pneumonia
- Infection (Tuberculosis)
- Injury to the ribs
- Lung contusions
- Pleural effusion
- Pulmonary embolism
- Radiation therapy
- Rheumatoid lung disease
- Tumours (benign or malignant)
How does asbestos exposure result in pleural thickening?
Pleural thickening can occur as a result of prolonged exposure to asbestos over an extended period of time.
Every day various dust particles enter the respiratory system as a result of inhalation. Larger particles are trapped in the nasal passages but smaller particles are able to pass the larynx and enter the main airways. Some of these are removed by the body’s natural defence mechanism; the particles are trapped in the mucus which lines the airways and the mucus containing asbestos fibres is then pushed upwards by the cilla and it is then swallowed or expectorated.
Some smaller dust particles are able to bypass these mechanisms and enter the lungs. The body’s natural defence mechanisms are able to eject larger asbestos fibres but unfortunately some asbestos fibres are so tiny that they are able to bypass these mechanisms and continue into deeper parts of the lung during inhalation.
These tiny particles (which tend to be long and thin in structure) are so small that they are invisible to the human eye. Workers who report being able to see clouds of asbestos dust in the air would not have been able to see the tiny fibres which are capable of bypassing the bodies defence mechanisms but instead would have been able to see the larger fibres which invariably indicated the additional presence of the smaller, invisible fibres.
These tiny particles of asbestos, measuring only microns (a micron is one millionth of a metre) in diameter and length, once inhaled, are capable of proceeding through the respiratory system to the alveoli, piercing the cell walls and migrating into the pleura where they become lodged.
The injury caused by the presence of asbestos fibres is understood to induce the sub-pleural fibroblasts and mesothelial cells to produce scar tissue and collagen deposition, resulting in sub-pleural thickening.
Diffuse pleural thickening does not develop immediately after exposure to asbestos. The latency period for the disease is around 20 to 40 years from the date of first exposure, although this can occur sooner if it develops following asbestos-related pleural effusion. Where asbestos related pleural effusion has been present and has resolved scar tissue is often formed on the pleura.
Who is at risk of developing pleural thickening?
You are at risk of developing diffuse pleural thickening if you have been subject to prolonged asbestos exposure.
Individuals involved in the following professions are generally thought to be at risk of asbestos exposure (please note that this is not an exhaustive list of occupations where asbestos exposure may occur):-
- Building surveyors
- Cable layers
- Carpenters or joiners
- Computer installers
- Construction workers
- Demolition workers
- Fire or burglar alarm installers
- Fire fighters
- Gas fitters
- General maintenance staff
- Heating and ventilation engineers
- Insulation workers
- Roofing contractors
- Ship yard
- Shop fitters
- Telecommunication engineers
- Textile workers
In rare circumstances environmental or household exposure to asbestos may also result in the development of diffuse pleural thickening.