Imaging Studies

• Chest radiograph

  • Effusions >150-200 mL usually are apparent as blunting of the costophrenic angle on upright posteroanterior (PA) chest radiographs.

  • Moderate to large pleural effusions might appear as a homogenous increase in density over the lower lung fields on a supine chest radiograph.

  • Apparent elevation of the hemidiaphragm, lateral displacement of the dome of the diaphragm, or increased distance between the apparent left hemidiaphragm and the gastric air bubble suggest subpulmonic effusions.

  
  

• Lateral decubitus films more reliably detect smaller pleural effusions.

  • Layering of

    an effusion on lateral decubitus films defines a freely flowing effusion and, if the layering fluid is 1 cm thick, indicates an effusion that is amenable to thoracentesis.

  • Failure

    of an effusion to layer on lateral decubitus films indicates loculated pleural fluid.

• Chest radiographs can reveal other diagnostic clues to the cause of an effusion.

  • Large unilateral effusions typically shift the mediastinum to the contralateral hemithorax. Lack of mediastinal shift with an apparent large effusion suggests bronchial obstruction,infiltration of the lung with tumor or inflammatory cells, mesothelioma, or a fixed mediastinum from tumor or fibrosis.

  • Bilateral effusions accompanied by enlarged heart shadows usually are caused by congestive heart failure.

  • Pleural plaques and calcifications usually indicate previous asbestos exposure.

  • Radiographic findings of pneumonia or malignancy suggest these processes as etiologies for the associated effusion.

• Computed tomography provides detailed information about pleural and parenchymal lesions, and interventional radiologists can use it to direct small drainage catheters into loculated pleural collections.