Aetiology

A variety of diseases and medications may be responsible for accumulation of fluid in the pleural cavity (1)

The causes of a pleural effusion can be divided into exudative and tansudative - classically exudates having a protein level >30 g/l and transudates <30 g/l. A more accurate differentiation can be made using Light’s criteria (2)

If the protein content of the effusion is not known then the most common causes of a pleural effusion are:

• infection, e.g. underlying pneumonia
• tuberculous pleurisy
• infarction of underlying lung
• malignancy
• organ failure, e.g. cardiac, liver, kidney

Although there are various conditions which lead to effusions, majority are idiopathic and tend to follow a benign course (1)

Reference:

• (1) Saguil A, Wyrick K, Hallgren J. Diagnostic approach to pleural effusion. Am Fam Physician. 2014;90(2):99-104
• (2) Medford AR, Maskell N. Pleural effusion. Postgrad Med J. 2005;81(961):702-10