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Small effusions are usually asymptomatic while large effusions reliably cause dyspnea with or without pleuritic chest pain. The presentation depends on the cause of the effusion. Parapneumonic effusions are accompanied by the signs and symptoms of pneumonia while effusions related to neoplasm, HF, PE or rheumatologic disease are accompanied by signs of those underlying diseases.


  1. Pathophysiology of pleural effusions vary by etiology but may be due to one or any combination of the following disruptions in capillary Starling forces:

    1. Increased capillary permeability

    2. Increased capillary hydrostatic pressure

    3. Decreased capillary oncotic pressure

    4. Increased pleural oncotic pressure (eg, due to pleural metastases)

    5. Increased negative intrapleural (hydrostatic) pressure

    6. Disruption of pulmonary lymphatics

  2. The most common causes of pleural effusions with their approximate yearly incidence are listed in Table 9-12.

  3. A useful way of organizing the differential diagnosis is by whether the effusion is exudative or transudative.

    1. Exudative effusions are caused by increased capillary permeability or disruption of pulmonary lymphatics.

    2. Transudative effusions are caused by increased hydrostatic pressure, decreased oncotic pressure, or increased negative intrapleural pressure.

    3. Table 9-13 lists common transudative and exudative effusions.

  4. Exudative effusions commonly complicate the following diagnoses:

    1. Pneumonia

      1. Any effusion associated with pneumonia, lung abscess, or bronchiectasis is considered a parapneumonic effusion.

      2. Empyemas are parapneumonic effusions that have become infected.

      3. Empyemas, and certain parapneumonic effusions called complicated parapneumonic effusions, are more likely to form fibrotic, pleural peels. The diagnostic criteria for these types of effusions are described in the Evidence-Based Diagnosis section.

      4. Parapneumonic effusions accompany 40% of all pneumonias, while empyemas are rare complications.

      5. Effusions are more likely to form and are more likely to become infected if the treatment of the underlying pneumonia is delayed.

      6. The bacteriology of parapneumonic effusions is shown in Table 9-14.

    2. Malignancy

      1. Cancers most commonly associated with effusions are

        1. Lung

        2. Breast

        3. Lymphoma

        4. Leukemia

        5. Adenocarcinoma of unknown primary

      2. The effusion may occur as the presenting symptom of the cancer or occur in patients with a previously diagnosed malignancy.

      3. The presence of a malignant effusion is generally a very poor prognostic sign.

    3. PE

      1. Effusions are present in 26–56% of patients with PE.

      2. Most commonly, effusions accompany PE in patients with pleuritic pain or hemoptysis.

    4. Viral infections

      1. Considered to be a common cause of effusions

      2. Historically, these have been difficult to diagnose but with the widespread availability of respiratory viral panel testing this may change.

      3. Usually diagnosed in patients with febrile or nonfebrile illness with a transient effusion and negative evaluation for other causes.

      4. Other clues such as atypical lymphocytes, monocytosis, and leukopenia are helpful in diagnosing viral infection.

    5. image A pleural effusion should only be diagnosed as viral in an appropriate clinical setting when more serious causes of effusion have been ruled out.

    6. CABG

      1. Pleural effusions develop in up to 90% of patients immediately following CABG.

      2. Can be left sided or bilateral

      3. Usually resolve spontaneously

    7. Other diseases that are not common causes of exudative pleural effusions include


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