Subpulmonic pleural effusion


Subpulmonic effusions are also called infrapulmonary effusions. Minimal to moderate subpulmonic effusions can be missed unless carefully kept in mind.

Many signs have been described in literature to diagnose this condition on a plain frontal chest x-ray obtained in the upright position.

  • Raised dome of diaphragm, easier to diagnose when seen on left side, but a difference of two intercostal spaces higher on right side also raises the suspicion of subpulmonic fluid.
  • Increased distance between left diaphramatic outline and the fundal gas bubble in the stomach.
  • Abrupt termination of lung markings at the diaphragmatic interface attributable to fluid being denser to the normal translucency of lung base.
  • The pseudodiaphragm (visceral pleural interface) appears flattened especially at medial margins, with blunting of the cardiophrenic angle.
  • The pseudodiaphragm shows a more lateral peak - 'lateralization of diaphragmatic apex'
  • Crowding of lung markings at lower zones in cases of moderate to large subpulmonic effusions.
  • In some cases parietal pleural calcifications may help to delineate and diagnose the effusion.
  • Lateral chest radiograph may show blunting of the posterior costophrenic recess.

In larger subpulmonic effusions, there may be blunting of the lateral costophrenic angle on frontal x-ray of chest.