CXR AP (left) shows the hypoplastic lung bud which cannot immediately expand to fill the hemithorax in the apex of the left hemithorax and therefore there is also air in the left pleural space. Note that this is not a pneumothorax and should not be drained via a chest tube. CXR AP obtained 2 days later (right) shows the left pleural space is now filled with fluid rather than air, and again this should not be drained by a chest tube. As the lung bud expands, the pleural effusion will decrease in size.
Pediatric Imaging 