Trapped lung

Clinical History

63-year-old man with past medical history of renal cell carcinoma s/p bilateral nephrectomy on haemodialysis, hypertension, and type II diabetes mellitus presented after a syncopal episode with left flank and rib pain. The patient had decreased breath sounds of the right lung base, crackles of the left lung base.

Imaging Findings

Presentation chest X-ray showed a large right pleural effusion with compressive atelectasis (Fig. 1); thoracentesis was suggested and performed. Immediately following thoracentesis, the patient's chest X-ray showed development of a hydropneumothorax. The pneumothorax component did not change with inspiration or expiration (Fig. 2). A right-sided chest tube was placed a few days later without successful lung expansion (Fig. 3), although it did resolve the pleural effusion; this chest tube was likely unwarranted as the diagnosis of trapped lung was apparent from the chest X rays immediately following thoracentesis.

Discussion

A. Background: A trapped lung occurs when there is pleural space inflammation resulting in visceral pleural encasement with a fibrous peel preventing the lung from expanding in the chest wall during fluid removal. A negative pressure gradient is created causing a chronic fluid-filled pleural space [2]. The fibrous visceral pleura from chronic inflammation results in separation from the parietal pleura and the space fills with fluid resulting in a hydropneumothorax. When the fluid is removed there is a resulting pneumothorax since the lung cannot expand [1].

B. Clinical Perspective: Clinical presentations of trapped lung include chest pain, dyspnoea on exertion and decreased breath sounds on the affected side. However, patients may be asymptomatic or have minimal dyspnoea with exertion. To diagnose trapped lung, there must be no active pleural inflammatory or malignant process and the lack of expansion must be stable over time [3]. Imaging is needed to make the proper diagnosis and distinguish trapped lung from other process with similar presentations such as lung entrapment which is a complication of active pleural inflammation, malignancy or haemothorax [4].

C. Imaging Perspective: Computed tomography and plain film radiographs can be used to assist in the diagnosis of trapped lung. Trapped lung does not appear larger on expiration than on inspiration in comparison to pneumothorax. The visceral pleural line delineates the scarred lung contour. Visceral pleural peel, pneumothoraces and lobar atelectasis may be visualized on radiography of trapped lung distinguishing it from other entities [2]. Manometry has also been used to assist in the diagnosis of trapped lung [4].

D. Outcome: The therapeutic approach to treating trapped lung depends on the clinical situation. The definitive treatment is surgery including pleurectomy and decortication to remove the fibrosed visceral pleura from the lung to relieve pressure and allow for expansion of the trapped lung [1]. Extended drainage by pleural catheter is another treatment option usually reserved for patients that are symptomatic but are poor surgical candidates [2].

E. Take Home Message: Trapped lung should be included in the differential diagnosis of a patient with a radiographically stable pneumothorax after pleural fluid drainage, when lung expansion would be expected. Other clinical entities can initially mimic trapped lung such as lung entrapment and further imaging and other diagnostic tests such as manometry can determine the clinical diagnosis. Making the proper diagnosis initially will help guide management.

Differential Diagnosis List

Final Diagnosis

Trapped lung (pneumothorax ex vacuo)

URL:	https://www.eurorad.org/case/13940
DOI:	10.1594/EURORAD/CASE.13940
ISSN:	1563-4086