Pleural thickening refers to a condition where the pleura, the thin membranes surrounding the lungs, become abnormally thick. These membranes consist of two layers: one adheres directly to the lung surface (visceral pleura), and the other lines the inside of the chest wall (parietal pleura). A small, fluid-filled space, known as the pleural space, lies between these layers, allowing the lungs to expand and contract smoothly during breathing.
When scarring or inflammation occurs within these membranes, the pleura can stiffen and thicken. This change can sometimes restrict the lungs’ ability to fully expand, potentially leading to symptoms like shortness of breath or chest tightness. Pleural thickening is not a disease in itself but rather a sign of a past injury or underlying medical condition.
It can be localized to a small area or spread diffusely across larger regions of the pleura, and its causes are varied, ranging from environmental exposures to infections and physical trauma.
Asbestos-Related Pleural Thickening
Asbestos exposure is a prominent cause of pleural thickening, particularly the diffuse form. Asbestos is a group of naturally occurring mineral fibers historically used in various industries, including construction, for its heat resistance and insulating properties. When tiny asbestos fibers become airborne and are inhaled, they can reach the lungs and become trapped in the pleural lining.
Once lodged in the pleura, these fibers can cause chronic irritation and inflammation over many years. This persistent irritation leads to the formation of scar tissue, resulting in the thickening of the pleural membranes. This scarring can manifest as diffuse pleural thickening, affecting large areas of the pleura, or as localized patches known as pleural plaques. Pleural plaques are benign, non-cancerous areas of thickening and serve as a strong indicator of past asbestos exposure. Diffuse pleural thickening, in contrast, involves widespread scarring across significant portions of the lung lining, which can substantially impair lung function and cause symptoms like breathlessness.
The development of asbestos-related pleural thickening often has a long latency period, meaning symptoms may not appear until 20 years or more after the initial exposure. Individuals who worked in occupations involving asbestos, such as carpenters, electricians, or shipbuilders, are at higher risk.
Inflammatory and Infectious Causes
Inflammation and infection of the pleura are common pathways leading to pleural thickening. The body’s natural response to inflammation involves the formation of fibrous tissue, which, in the pleura, can result in scarring and thickening. This process often begins with conditions like pleurisy, which is inflammation of the pleura, typically causing sharp chest pain.
Viral or bacterial infections are frequent culprits behind pleurisy and subsequent pleural changes. For example, severe or recurrent cases of pneumonia can lead to significant pleural inflammation. As the body fights the infection, inflammatory cells and proteins accumulate in the pleural space, leading to fibrous adhesions and thickening that may persist even after the infection resolves.
Tuberculosis (TB) is another infectious disease known to cause pleural thickening. TB infection of the pleura, known as tuberculous pleurisy, can result in substantial inflammation and the subsequent formation of scar tissue. This scarring can be quite extensive, sometimes leading to calcification within the thickened pleura.
Traumatic and Medical Causes
Beyond asbestos and infections, various traumatic injuries and medical interventions can also contribute to pleural thickening. Traumatic events to the chest, such as rib fractures or blunt force trauma, can directly damage the pleura. The healing process following such injuries involves inflammation and scar tissue formation, which may lead to localized areas of pleural thickening. Similarly, bleeding into the pleural space, known as hemothorax, can also instigate fibrosis and thickening as the blood is reabsorbed and the pleura repairs itself.
Surgical procedures involving the chest, particularly those that open the chest cavity like a thoracotomy, can also induce pleural thickening. The manipulation of tissues and the body’s natural healing response to the surgical trauma can result in adhesions and scarring of the pleura.
Certain medical conditions and treatments can also cause pleural thickening. Autoimmune diseases, where the immune system mistakenly attacks the body’s own tissues, can affect the pleura. Conditions like lupus or rheumatoid arthritis can cause chronic inflammation of the pleural membranes, leading to fibrosis. Additionally, specific medications can sometimes induce pleuritis, which may then progress to pleural thickening. Radiation therapy to the chest, often used in cancer treatment, is another recognized cause, as radiation can damage pleural cells and trigger a fibrotic healing response.