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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Article information

rID: 20994
System: Chest
Section: Gamuts
Synonyms or Alternate Spellings:
  • Unexpanded lung
  • Unexpandable lung

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Cases and figures

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    Case 1
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    Case 2: with basal pneumothorax
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    Case 3
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    Case 4
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