An entrapped lung is one that cannot fully expand to fill the chest cavity because a layer of scar-like tissue, tumor, or inflammatory debris coats its outer surface and physically holds it in place. The condition traps fluid in the space between the lung and the chest wall, and because the lung cannot re-inflate even when that fluid is removed, standard drainage alone does not solve the problem. Roughly 30 percent of people with cancer-related fluid around the lungs develop some degree of lung entrapment, making it a common complication in oncology and a frustrating one to manage.
Why Doctors Use Two Different Names
If you read medical literature on this topic, you will run into two terms that sound interchangeable but are not. “Trapped lung” in the strict clinical sense refers to a lung held down by a fibrous peel on the visceral pleura (the membrane that covers the lung surface) that formed after a past episode of inflammation has already resolved. There is no active infection, no active cancer involvement on the pleura, and no ongoing inflammatory process. The scar tissue itself is the whole problem.
“Lung entrapment,” by contrast, describes the same physical restriction, except it arises from an ongoing disease process. Active pleural infection, spreading cancer, or unresolved inflammation produces the peel that prevents the lung from expanding. In these cases, the underlying disease is the primary clinical concern; the inability of the lung to expand is a complication layered on top of it.
Both conditions fall under the umbrella term “unexpandable lung,” which also includes situations where a tumor blocks a major airway from the inside (causing a lobe to collapse) or where chronic collapse has left a portion of lung stiff and immobile.1PubMed Central. The unexpandable lung The distinction matters because treatment strategies differ. A trapped lung from old scar tissue may need a mechanical solution, while an entrapped lung from active disease may respond, at least partly, to treating the cancer or infection driving it.
What Causes It
Any process that injures the pleura and triggers scarring can eventually entrap the lung. The most common scenarios fall into a few broad categories:
- Pleural infection (empyema): Pus accumulates between the lung and chest wall, usually following pneumonia. If the infection is not drained early enough, the inflammatory debris organizes into a thick rind that encases the lung.
- Malignancy: Pleural metastases from lung, breast, or other cancers can coat the visceral pleura in tumor tissue. Up to 30 percent of patients with metastatic cancer develop pleural involvement, and when malignant adhesions entrap the lung and fluid becomes loculated, the condition has been called an “oncothorax.”2PubMed Central. Management of Malignant Lung Entrapment, the Oncothorax
- Prior surgery or trauma: Blood left in the pleural space after chest surgery or injury (retained hemothorax) can organize into fibrous tissue over weeks.
- Chronic inflammatory conditions: Autoimmune pleuritis, asbestos exposure, or radiation therapy to the chest can all produce long-term inflammation that gradually thickens the pleural lining.
- Hepatic hydrothorax: Fluid crossing from the abdomen into the chest in people with advanced liver disease sometimes leads to chronic pleural inflammation and, eventually, a fibrous layer along the visceral pleura that traps the lung.3PubMed Central. Pneumothorax ex-vacuo or “trapped lung” in the setting of hepatic hydrothorax
Whether the restricting layer is a benign fibrous cortex or a sheet of malignant tumor, the mechanical result is the same: the lung sits compressed and cannot re-inflate when fluid is removed from around it.4PubMed. Pleurectomy decortication in the treatment of the “trapped lung” in benign and malignant pleural effusions
How the Fibrous Peel Develops
When the pleura is injured, the body launches a repair process that can go wrong. Normally, the mesothelial cells lining the pleura act as a smooth, low-friction surface. After infection or inflammation, those cells can be damaged or stripped away entirely, exposing the underlying tissue. Fibrin, the same protein that forms blood clots, deposits on the exposed surface. Strands of fibrin can bridge the gap between the visceral and parietal pleura, forming adhesions.
Fibroblasts then migrate along those fibrin strands and begin producing collagen, gradually converting what started as a soft, spongy layer into a tough, inelastic rind. In animal models, the severity of this fibrosis tracks closely with how badly the mesothelial surface was damaged in the first place. When mesothelial cells were merely roughened, fibrosis was mild; when they were completely stripped away, fibrin deposition and eventual scarring were far more extensive.5Experimental and Molecular Pathology. The histology of experimental pleural injury with tetracycline, empyema, and carrageenan
A growth factor called TGF-β1 appears to be a key driver of this process. In experimental empyema, levels of TGF-β1 in the pleural fluid rose sharply before the pleura began to visibly thicken. The rise in this growth factor preceded and then correlated tightly with both the microscopic thickness of the pleural peel and the number of fibroblasts present.6American Journal of Respiratory and Critical Care Medicine. Pleural Fluid Transforming Growth Factor–β1 Correlates with Pleural Fibrosis in Experimental Empyema That finding matters because it suggests a window of opportunity: if the infection or inflammation can be treated aggressively before fibroblasts take hold and TGF-β1 levels spike, the progression toward a permanent restrictive peel might be prevented.
How Doctors Identify an Entrapped Lung
A pleural effusion that keeps coming back after drainage is suspicious, but recurrence alone does not confirm lung entrapment. The key diagnostic question is whether the lung can re-expand once fluid is out of the way. Several tools help answer that question.
Pleural Manometry
During a thoracentesis (needle drainage of pleural fluid), a manometer can measure the pressure inside the pleural space as fluid is withdrawn. In a normal situation, pleural pressure drops gradually and the lung re-expands to take up the vacated space. When the lung is trapped, pressure drops steeply with each unit of fluid removed because the lung cannot follow the receding fluid. This steep drop is measured as elevated pleural elastance. In one case series, elastance ranged from 19 to 149 cm Hâ‚‚O per liter of fluid removed, all well above normal.7PubMed. Characteristics of trapped lung: pleural fluid analysis, manometry, and air-contrast chest CT Manometry is considered critical for distinguishing trapped lung from lung entrapment and for guiding further management.8PubMed. Pleural manometry in patients with pleural diseases – the usefulness in clinical practice
Imaging
Air-contrast chest CT, in which air is allowed into the pleural space after some fluid is removed, can reveal abnormal thickening of the visceral pleura. In the same case series, every patient with confirmed trapped lung showed abnormal visceral pleural thickness on this type of scan.9PubMed. Characteristics of trapped lung: pleural fluid analysis, manometry, and air-contrast chest CT
Pleural Ultrasound
A newer approach uses ultrasound before any fluid is drained. By tracking how much the lung surface moves with breathing, clinicians can predict entrapment without waiting for a failed drainage attempt. One study found that speckle-tracking ultrasound, a technique that follows tiny tissue movements frame by frame, could identify entrapped lung with a sensitivity of about 71 percent and specificity of 85 percent. That outperformed both conventional M-mode ultrasound and pleural elastance measurement alone.10PubMed. Novel use of pleural ultrasound can identify malignant entrapped lung prior to effusion drainage The ability to catch entrapment before drainage matters because it changes the treatment plan: a patient with known entrapment may skip a traditional thoracentesis entirely and go straight to a longer-term solution.
What Goes Wrong During Drainage
When unexpandable lung is not recognized before a thoracentesis, the drainage itself can cause problems. As fluid leaves the pleural space and the lung fails to follow, the pressure in the space drops dramatically. The patient often develops sharp anterior chest pain, which is a signal to stop draining. If drainage continues, the extreme negative pressure can pull gas from surrounding tissues into the pleural space, creating what is called a pneumothorax ex vacuo. Unlike a regular pneumothorax, which is caused by a leak of air from a hole in the lung, pneumothorax ex vacuo results from the vacuum effect of a lung that simply cannot expand.11PubMed Central. The unexpandable lung It usually resolves on its own and does not require a chest tube for the air itself, but the episode can be alarming for the patient and is avoidable if manometry or pre-drainage ultrasound flags the entrapment in advance.
Indwelling Pleural Catheters
Because the lung cannot re-expand and seal the pleural space, procedures like chemical pleurodesis, where an irritant is injected to glue the two pleural layers together, typically fail in entrapped lung. The two surfaces never come into contact, so they cannot fuse. Indwelling pleural catheters (IPCs) have become the treatment of choice in this situation.12Clinics in Chest Medicine. Tunneled Pleural Catheters / Indwelling Pleural Catheters
An IPC is a thin, flexible tube tunneled under the skin into the pleural space. The external end has a one-way valve that can be connected to a vacuum bottle, allowing the patient or a caregiver to drain fluid at home, usually every one to three days. In one series of patients with malignant pleural effusion and trapped lung, all but one reported improved breathlessness and exercise tolerance after IPC placement. Catheters stayed in place for an average of about 115 days, ranging from 15 to 234 days. Complications were uncommon but included catheter blockage, localized skin breakdown, and infection around the catheter site.13PubMed. Use of an implantable pleural catheter for trapped lung syndrome in patients with malignant pleural effusion
A larger study of 52 patients with malignant effusions and trapped lung reported symptomatic relief in 94 percent. Average breathlessness scores improved meaningfully, and complications were relatively modest, including catheter blockage, localized infection, and surgical emphysema in a small number of patients.14PubMed. Management of malignant pleural effusion associated with trapped lung syndrome For patients with advanced cancer and limited life expectancy, this approach provides palliation without requiring repeated hospital visits for drainage.
Fibrinolytic Therapy for Organized Effusions
When the problem is not just a peel on the lung surface but also thick, loculated fluid that has been walled off into pockets by fibrin strands, draining through a standard chest tube may be ineffective. In these cases, a combination of clot-dissolving medication (tissue plasminogen activator, or tPA) and an enzyme that breaks down DNA from dead cells (DNase) can be infused through the chest tube directly into the pleural space. The tPA dissolves fibrin barriers while the DNase reduces the viscosity of the infected fluid, allowing it to flow more freely to the drain.
A large randomized trial established that this combination, given twice daily through a chest tube, successfully managed over 90 percent of patients with pleural infection without the need for surgery.15Annals of the American Thoracic Society. Dose De-escalation of Intrapleural Tissue Plasminogen Activator Therapy for Pleural Infection. The Alteplase Dose Assessment for Pleural Infection Therapy Project Follow-up work has explored whether the same approach works for complicated pleural collections arising from abdominal infections rather than pneumonia, extending the potential applications.16Annals of the American Thoracic Society. Safety and Efficacy of Tissue Plasminogen Activator and DNase for Complicated Pleural Effusions Secondary to Abdominal Pathology Fibrinolytic therapy is now widely used across many centers as a first-line option before escalating to surgery.17PubMed Central. Pleural Space Diseases and Their Management: What is the Role of Intrapleural Fibrinolytic Therapy?
It is worth noting what fibrinolytic therapy can and cannot do. It breaks down the fibrin partitions inside the fluid collection, which improves drainage. But if the lung is already encased in a mature, collagen-dense peel, dissolving fibrin in the fluid will not strip the rind off the lung. The therapy is most effective in the organizing phase of empyema, before a permanent fibrotic cortex has formed. Once a thick peel has solidified, a mechanical approach is usually needed.
Surgical Decortication
Decortication is the surgical removal of the restrictive peel from the lung surface. When successful, the lung re-expands to fill the chest cavity, fluid stops accumulating, and breathing improves substantially. Historically this was done through an open thoracotomy, a large incision that required spreading or cutting the ribs, with significant postoperative pain and a long recovery period.
Over the past two decades, video-assisted thoracoscopic surgery (VATS) has become a viable alternative for many patients. VATS decortication uses small incisions and a camera to guide the surgeon in peeling the fibrous layer off the lung. Compared with open thoracotomy, VATS is associated with less postoperative pain, shorter hospital stays, and faster recovery while achieving comparable success rates when the peel can be completely removed.18IntechOpen. Pleural Decortication in the Era of Minimally Invasive Thoracic Surgery: The Role of VATS Earlier studies also demonstrated that VATS decortication is feasible and beneficial specifically in chronic empyema, the same infection-related scarring that frequently causes entrapped lung.19PubMed. Thoracoscopic decortication: a role for video-assisted surgery in chronic postpneumonic pleural empyema
Not everyone is a candidate for decortication. In cancer-related entrapment, the malignant adhesions holding the lung down are often not amenable to surgical peeling. The tumor may be too diffuse or too intimately involved with the lung surface to strip cleanly, and the patient’s overall condition may not tolerate a major operation. For those patients, an indwelling pleural catheter remains the standard approach.20PubMed Central. Management of Malignant Lung Entrapment, the Oncothorax In benign disease, however, decortication can be curative when performed at the right time, ideally after the acute infection has been controlled but before the peel becomes so thick and calcified that removal risks damaging the underlying lung.
Why Timing Matters So Much
The thread running through every treatment discussion is timing. In empyema, early aggressive drainage and antibiotics may prevent the fibrous peel from ever forming. Fibrinolytic therapy works best in the organizing phase, when fibrin barriers are still relatively soft. VATS decortication is most successful when the peel is mature enough to peel cleanly but not so old that it has become calcified or fused to the lung parenchyma. Wait too long and the options narrow considerably.
In malignant entrapment, the timing calculus is different. The disease is usually progressive, and the goal shifts from cure to comfort. The question becomes how to manage recurring fluid accumulation with the least burden on the patient. An IPC placed early in the course can prevent repeated emergency drainage procedures and the discomfort that comes with them. Waiting until the patient is already in severe respiratory distress before placing a catheter means lost time that could have been spent more comfortably at home.
Living with an Indwelling Catheter
For patients who end up with a long-term IPC, the practical realities deserve attention. Drainage is typically performed at home by the patient or a family member using single-use vacuum bottles. The process takes about 15 to 20 minutes and is done on a schedule, usually every one to three days depending on how fast fluid reaccumulates. Most people report that the catheter itself causes minimal day-to-day discomfort once the insertion site has healed.
The caregiver burden, however, is real. In one survey, the vast majority of IPC patients relied on unpaid caregivers, usually family members, to help with drainage. Some patients reported that the catheter restricted their activities, and for about half of those, the limitation had a meaningful negative effect on their quality of life.21PubMed. A Survey-Based Study of Patient-Centered Costs Associated With Indwelling Pleural Catheters Showering, swimming, and certain types of physical activity require extra care to keep the site clean and dry. Infection at the catheter site, while uncommon, remains a persistent risk that requires vigilance.
Some patients with non-malignant effusions do eventually achieve spontaneous pleurodesis through their IPC. As regular drainage keeps the pleural surfaces in closer contact, inflammation around the catheter can cause the visceral and parietal pleura to fuse. When fluid production drops to near zero, the catheter can be removed. This outcome is less likely in patients whose lungs are truly trapped, since the surfaces never fully appose, but it does occasionally happen in cases with partial entrapment.
The Special Problem of Cancer-Related Entrapment
Lung entrapment from malignancy carries an additional layer of complexity. The pleural space in patients with nonexpandable lung and a malignant effusion is usually under unusually high negative pressure. This pressure difference can pull extra fluid from surrounding blood vessels into the pleural space through basic fluid physics, adding a transudative effusion on top of the malignant one.22Journal of Thoracic Oncology. Trapped lung, now also called nonexpandable lung The result is a “double source” of fluid accumulation that can be difficult to control.
Systemic cancer treatment, including chemotherapy and targeted therapy, may reduce the malignant component of the effusion but typically cannot reverse the mechanical entrapment once a tumor rind has formed. Even patients who respond well to systemic therapy may continue to need their IPC for palliation. Coordination between the oncology team and the interventional pulmonologist is critical here. If a patient is expected to have a durable response to systemic therapy, some clinicians hold off on aggressive local interventions and reassess once the tumor burden has been reduced. If the prognosis is short, the focus shifts entirely to comfort.