Pleural Effusion

Preliminary Diagnosis: Pleural effusion

I. What imaging technique is first-line for this diagnosis?

Chest radiograph

II. Describe the advantages and disadvantages of this technique for diagnosing pleural effusion?


  • Fluid may be easily detected blunting the lateral or posterior costophrenic sulcus.

  • Large effusions will cause a mediastinal shift.

  • Common etiologies, such as congestive heart failure, are easily detected.

  • The lateral decubitus radiograph is able to detect as little as 10 mL of fluid.

  • This is a simple and cost-effective examination for diagnosis.


  • Supine radiographs obtained in critically sick patients often require 500 mL of fluid for diagnosis.

  • Does not reveal if a pleural effusion is transudative or exudative.

  • It may be difficult to detect if the effusion is loculated.

III. What are the contraindications for the first-line imaging technique?

  • No significant contraindications exist.

  • Pregnancy may be a relative contraindication, but lead shielding can be provided.

IV. What alternative imaging techniques are available?

  • Noncontrast CT

  • Ultrasound

  • MRI

V. Describe the advantages and disadvantages of the alternative techniques for diagnosing pleural effusion.

Noncontrast CT


  • Can demonstrate small effusions (10 mL of fluid or less).

  • Can demonstrate complex, loculated collections and pleural thickening.

  • Assesses the pleura for thickening and mass, the chest wall, and mediastinum for associated disease.

  • Fluid-fluid levels can suggest hemorrhage, and air-fluid levels can be seen with bronchopleural fistula, empyema, and trauma.


  • Does not reliably distinguish transudates from exudates.

  • Exposure to ionizing radiation.



  • Can demonstrate effusions without radiation exposure.

  • May demonstrate loculations and pleural thickening.

  • Preferred imaging modality for thoracentesis.

  • Quick and easy to perform.


  • Can be difficult in patients with large body habitus or those who are uncooperative.

  • Echogenic fluid suggests exudate, but US often cannot distinguish exudate from transudate.



  • Can accurately demonstrate small effusions.

  • Demonstrates pleural thickening and tumors, and evaluates the mediastinum and chest wall for invasion.

  • May help determine the age of blood in a hemothorax.


  • Expensive.

  • Time consuming.

  • Requires significant patient cooperation to minimize motion artifact.

  • This is a difficult examination for critically sick patients or those with claustrophobia.

VI. What are the contraindications for the alternative imaging techniques?

Noncontrast CT

  • Renal failure increases the risk of contrast induced nephropathy.

  • Pregnancy.

  • Contrast allergy may be a relative contraindication.


  • No significant contraindications exist.


  • Contraindicated in patients with non-MR compatible hardware.

  • If intravenous contrast is given, there is the risk of acute renal failure due to the risk of nephrogenic systemic fibrosis.

  • Relative contraindication in the first trimester of pregnancy.

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