Trapped lung, also known as unexpandable/unexpanded lung, is a term used where there is non-expandable lung after fluid removal, often thoracentesis. It is similar to but not entirely synonymous with the term lung entrapment, which is a similar condition but caused by active pleural disease rather than pleural inflammation from remote disease.
Trapped lung develops as a sequela of pleural space inflammation from remote disease resulting in the development of a mature, fibrous membrane that impedes the lung from re-expanding. This creates a negative pressure environment in the pleural space, which is filled with fluid creating a pleural effusion. Drainage of this pleural fluid will often result in unavoidable pneumothorax from parenchymal-pleural fistulae.
Commonly noted to be associated with post-thoracentesis pneumothorax, and may have the following features 4:
- visceral pleural peel (thickening)
- basal pneumothoraces
- ipsilateral volume loss
- lobar atelectasis
Pneumothoraces, if present, typically do not appear larger on expiratory images 1.
General imaging differential considerations include 1:
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.
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- 4. Heidecker J, Huggins JT, Sahn SA et-al. Pathophysiology of pneumothorax following ultrasound-guided thoracentesis. Chest. 2006;130 (4_MeetingAbstracts): 1173-84. doi:10.1378/chest.130.4.1173 - Pubmed citation