Pleural Effusion

Definition/diagnostic criteria Pleural effusion is defined as the accumulation of fluid between the layers of the pleura, the thin membranes lining the lungs and chest cavity. To diagnose pleural effusion, clinicians rely on a combination of clinical evaluation and imaging studies.

Epidemiology Pleural effusions are a common clinical problem in the UK, with an estimated incidence of 1.5 million cases annually. The condition can affect individuals of any age but is more common in older adults. Pleural effusions can result from a variety of causes, including heart failure, pneumonia, cancer and pulmonary embolism.

Diagnosis
Clinical features: Patients with pleural effusion may present with a range of symptoms, including dyspnoea, cough, chest pain and decreased breath sounds on the affected side. The severity of symptoms depends on the size and rate of fluid accumulation. Physical examination may reveal decreased chest expansion, dullness to percussion and reduced breath sounds over the affected area.

Investigations: Diagnosis and evaluation of pleural effusion typically involve imaging studies and pleural fluid analysis. Chest X-ray is the initial imaging modality of choice and can identify fluid accumulation in the pleural space. Ultrasound or computed tomography (CT) scanning may be used for further evaluation, particularly in cases of loculated effusions or when guided procedures are necessary.

Pleural fluid analysis is crucial for determining the nature of the effusion (transudative vs. exudative) and identifying the underlying cause. Tests conducted on pleural fluid include biochemistry, microbiology and cytology. Transudative effusions are typically associated with systemic conditions such as heart failure or cirrhosis, while exudative effusions are often due to local pleural pathology such as infection, malignancy or inflammation.

Typical abnormalities found in pleural effusion include elevated levels of lactate dehydrogenase (LDH) and protein in exudative effusions. Pleural fluid-to-serum protein and LDH ratios are used to differentiate between transudative and exudative effusions.

Treatment The treatment of pleural effusion depends on the underlying cause, the size of the effusion and the patient’s symptoms. Small, asymptomatic effusions may not require immediate intervention and can be managed with observation and treating the underlying condition.

For symptomatic effusions or large effusions, therapeutic thoracentesis may be performed to relieve symptoms. In cases of recurrent effusion, more definitive procedures such as pleurodesis or indwelling pleural catheter placement may be considered.

Antibiotics may be required for effusions secondary to bacterial infection, and specific therapy should be directed at the underlying malignancy in cases of malignant effusion.

Prognosis The prognosis of pleural effusion depends on the underlying cause and the patient’s overall health status. Effusions secondary to benign conditions such as pneumonia or heart failure generally have a good prognosis when appropriately managed. Malignant effusions tend to have a poorer prognosis, reflecting the advanced stage of underlying cancer.