Chest X-ray – Pleural Effusion

Pleura is a mesothelial lined sac that envelopes the lungs and comprises of 2 membranous walls i.e. visceral pleura and parietal pleura that encloses pleural space filled with pleural fluid. Pleural space contains about 0.3 ml/kg body weight of pleural fluid. The pleura is not visible on a normal CXR except where it forms part of a lung fissure or where the two lungs abut each other in the midline

pleural effusion xray

Erect frontal Chest X-ray:

  1. Obliteration of costophrenic angle: requires 200-300 ml pleural fluid
    • Concave meniscus (horizontal in case of hydropneumothorax)
  2. Massive pleural effusion: opacification of entire hemithorax and shifting of mediastinum to the opposite side
    • Causes “white-out” lung
    • Around 5-7 l of pleural fluid
  3. Lamellar pleural effusion: linear opacification paralleling the lateral aspect of lung
  4. Encysted pleural effusion: loculation within a fissure or elsewhere
    • Can be mistaken for lung tumor
  5. Subpulmonic effusion:
    • left: widening of the distance between gastric bubble and the superior margin of hemidiaphragm (normally < 7mm)
    • right: peak of the hemidiaphragm is shifted laterally

Lateral Chest X-ray:

Lateral films are able to identify a smaller amount of fluid as the costophrenic angles are deepest posteriorly

  • Can detect an effusion as small as 50 ml

Supine Chest X-ray:

Due to the effect of gravity, the pleural fluid is distributed throughout the posterior part of the pleural during supine position – this cause the hemithorax to appear whiter or paler grey compared to the normal side. Vessels are often visible through the shadowing.

  • Requires about 200 ml fluid

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