DDX of appearances of pneumothorax

Approach to the DDX of the different appearances of pneumothorax:

  • CXR upright: gravity drops lung inferiorly and medially and shows distinct pleural edge with no lung markings lateral to it
  • CXR decubitus: gravity drops lung inferiorly and shows distinct pleural edge with no lung markings superior to it
  • CXR cross-table lateral: gravity drops lung inferiorly and may show pleural edge with no lung markings anterior to it – but does not tell you which side the pneumothorax is on
  • CXR supine: gravity drops lung posteriorly and usually fails to reveal pleural edge, air accumulates anteromedially so pneumothorax can manifest itself as increased lucency throughout hemithorax / sharp heart border / deep sulcus sign = increased lucency in costophrenic angle
  • Note: if you suspect small pneumothorax on CXR supine get decubitus image with suspected side up to confirm
  • Note: tension pneumothorax is diagnosed when there is mediastinal shift which implies underlying tension