Lung entrapment is a type of unexpandable lung and typically refers to lung tissue enclosed by active pleural inflammation or pleural tumor 1. The thickened visceral pleura prevents full expansion of the lung and the diaphragm may be displaced affecting its function; both of these can cause dyspnea. The overall volume of the hemithorax may be increased.
The accompanying pleural fluid is an exudate, and pleural pressure becomes increasingly negative during aspiration because lung expansion is restricted. This can cause gas to enter the pleural cavity, either through the aspiration device or through microtears in the pleura. The resulting pneumothorax may be basal if lower lung expansion is restricted.
The term unexpandable lung also includes the semantically similar trapped lung. In this condition, non-inflamed visceral pleural thickening prevents full expansion of the lung and this is accompanied by abnormally low pleural pressure which causes a pleural transudate. The volume of the hemithorax is reduced.
These conditions may overlap: lung entrapment due to pneumonia with thick inflamed pleura can result in trapped lung if fibrosis complicates pleural healing. Pleural manometry and fluid analysis will distinguish the two conditions.
The third type of unexpandable lung is due to pulmonary causes such as atelectasis secondary to bronchial obstruction or pulmonary fibrosis.
Diagnosis
Pleural aspiration with manometry and fluid analysis differentiates between lung entrapment and trapped lung. Aspiration should cease if the patient experiences chest pain or if pleural pressure becomes excessively negative. Pleural pressure changes help to predict whether or not decortication or pleurodesis may be beneficial.
Radiographic features
Plain radiograph
Features of lung entrapment can include contralateral mediastinal shift, whereas in trapped lung there may be ipsilateral mediastinal shift.
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