Learning points

• Large unilateral pleural effusions are most often caused by malignancy; diagnostic pleural aspiration has a sensitivity of 60% for malignancy

• If pleural fluid cytology is negative, computed tomography of the chest should be done before the effusion is drained; this has a high sensitivity for malignant pleural disease

• Pleural fluid should initially be drained only for symptomatic relief; leaving some fluid in the pleural cavity allows the choice of a safe image guided biopsy or thoracoscopy

• Computed tomography guided biopsy and thoracoscopy (which can be done under conscious sedation by a physician) have high diagnostic yields for malignant pleural disease

• Computed tomography guided biopsy should be used when pleural thickening is present, with only a small volume of pleural fluid, or when thoracoscopy is not available

• Thoracoscopy should be used when a substantial amount of pleural fluid remains, if no nodularity is identified on chest computed tomography, and where both a diagnosis and a therapeutic procedure (talc pleurodesis) are needed