A trapped lung, also known as fibrothorax, is a chronic condition where the lung is physically unable to fully expand and fill the chest cavity during inhalation. This restriction occurs because a non-elastic, fibrous membrane forms around the lung’s outer surface, essentially encasing it in a stiff “peel.” The condition develops gradually after a severe inflammatory event and represents a long-term mechanical problem rather than an acute collapse. This chronic limitation on lung movement can severely compromise respiratory function and is a significant cause of persistent breathing difficulty.
The Underlying Mechanism of Lung Restriction
The lungs are enveloped by two thin, moist layers of tissue called the pleura, which allow smooth movement during breathing. The parietal pleura lines the inside of the chest wall, while the visceral pleura covers the lung’s surface. In a trapped lung, a mature, dense fibrous strip, often referred to as a “pleural rind,” develops on the visceral pleura following a remote inflammatory process. This fibrothorax effectively prevents the lung tissue from stretching and re-expanding to its normal volume.
This mechanical restriction is fundamentally different from a temporary lung collapse, such as an acute pneumothorax, where the lung might re-expand once air or fluid is removed. The inelastic fibrous tissue created by the body’s healing response permanently limits the lung’s ability to inflate. The lung remains compressed and unable to occupy the entire pleural space.
The restricted expansion often results in the presence of a chronic pleural effusion, which is an accumulation of fluid in the space between the two pleural layers. Since the lung cannot re-expand to fill the space left by the removed fluid, the effusion persists to maintain hydrostatic equilibrium within the chest cavity. This mechanism explains why simple fluid drainage does not resolve the issue, as the core problem is the restrictive peel on the lung itself.
Common Causes Leading to Trapped Lung
The development of this restrictive fibrous peel is a long-term consequence of a prior severe inflammatory event within the pleural space. One of the most frequent initiating events is a complicated parapneumonic effusion, which is a collection of fluid around the lung that becomes infected or highly inflamed, often associated with severe pneumonia. If this fluid is not adequately drained or treated, the body’s healing response can lead to excessive fibrin and collagen deposition.
Another major cause is a hemothorax, which is the presence of blood in the pleural space, typically following chest trauma or surgery. When blood remains in the chest cavity, its breakdown products trigger a strong inflammatory reaction that can result in the formation of the dense fibrous peel.
Malignant pleural effusions, where fluid accumulates due to cancer cells on the pleura, also frequently lead to a trapped lung due to chronic inflammation and fluid presence. Less common causes include thoracic surgery, exposure to radiation therapy in the chest area, and certain systemic conditions like uremia or autoimmune disorders such as rheumatoid pleuritis.
Identifying the Condition Through Symptoms and Testing
The most common symptom patients experience is progressive shortness of breath, medically known as dyspnea, which worsens over time. Patients often report limited exercise tolerance, finding that activities they once managed easily now cause significant breathlessness. While many patients are generally asymptomatic, the inability of the lung to fully expand means the patient is breathing with a reduced lung capacity.
To confirm the diagnosis, physicians rely on a combination of imaging and a diagnostic procedure. Standard chest X-rays and Computed Tomography (CT) scans may show thickening of the pleural layers, often referred to as a pleural rind. These imaging studies also reveal the persistent pleural effusion and a reduced volume of the affected lung.
The definitive diagnostic tool is thoracentesis, where a needle is inserted into the chest to drain the pleural fluid. During this procedure, the pressure within the pleural space is often measured, a technique known as pleural manometry. A characteristic finding in a trapped lung is that the pressure starts low and drops steeply as fluid is removed, indicating that the lung is unable to expand to compensate for the lost volume.
If the lung fails to re-expand on a post-procedure X-ray despite successful fluid removal, the diagnosis is confirmed. This failure to re-expand is sometimes seen as a small air pocket or pneumothorax ex vacuo on the scan. Pulmonary Function Tests (PFTs) will typically show a restrictive pattern, confirming the limitation on lung volume.
Medical and Surgical Management Options
The management approach for a trapped lung is determined by the patient’s symptoms and their overall health. For patients who are asymptomatic or have only mild, manageable shortness of breath, the condition is often monitored conservatively without immediate intervention. The risk of major surgery may outweigh the benefit if the patient’s lifestyle is not severely impacted.
For symptomatic patients who are not suitable candidates for major surgery due to other health issues, a palliative approach is often adopted. This usually involves the placement of an indwelling pleural catheter, which is a small, flexible tube that allows the patient to drain the chronic pleural effusion at home, providing continuous relief from breathlessness. This method manages the fluid accumulation but does not address the underlying mechanical restriction.
The only curative treatment that allows for full lung re-expansion is a major surgical procedure called decortication. This surgery involves the careful removal of the entire restrictive fibrous peel from the surface of the visceral pleura. The goal of decortication is to free the lung tissue, enabling it to fully inflate and restore normal respiratory mechanics.
Decortication can be performed using video-assisted thoracoscopic surgery (VATS) or a traditional open thoracotomy, depending on the thickness and extent of the fibrous peel. As a major intervention, the procedure carries risks, including prolonged air leaks, bleeding, and potential injury to the underlying lung tissue. However, in appropriately selected patients, successful decortication can lead to significant and lasting improvement in lung function and quality of life.