Subpulmonic effusion

Subpulmonic effusions are a pleural effusion that can be seen only on an erect projection. Rather than layering laterally and blunting the costophrenic angle, the pleural fluid lies almost exclusively between the lung base and the diaphragm.

Radiographic features

Chest radiograph

The fluid causes apparent elevation and flattening of the diaphragm. What appears to be the diaphragm actually represents the visceral pleura, and the true diaphragm is obscured by the presence of intrapulmonary fluid. The peak of the pseudo-diaphragm will lie lateral to the normal position. When located on the left, an increased distance may be seen between the pseudo-diaphragm and the gastric bubble.

Subpulmonic effusions will not be present on supine films, as the fluid should layer dependently if not loculated. If required, a decubitus projection can be performed to clarify the definite presence of a subpulmonic effusion.

Differential diagnosis

The differential on plain film includes causes of an elevated hemidiaphragm:

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Article Information

rID: 30402
System: Chest
Section: Gamuts
Synonyms or Alternate Spellings:
  • Infrapulmonary effusion
  • Subpulmonic effusions
  • Infrapulmonary effusions

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