Pleural Disease

Pleural disease comprises the disorders that affect the pleura, the two-layered serous membrane that lines the lungs (visceral pleura) and the inner chest wall (parietal pleura), and the thin fluid-filled space between them. Because the pleural space sits at the interface of the lung, chest wall, and circulation, it is affected by a wide range of conditions, and its disorders share a common toolkit of imaging, fluid analysis, and drainage.

Definition

Pleural disease refers to any pathological process involving the visceral or parietal pleura or the pleural space, manifesting most often as abnormal accumulation of fluid (effusion), air (pneumothorax), pus (empyema), or tissue (pleural thickening or tumour).

Scope

This area orients the reader to the principal pleural disorders covered as separate topics: pleural effusion (abnormal fluid in the pleural space), pneumothorax (air in the pleural space), empyema and pleural infection, and mesothelioma (the primary malignancy of the pleura). It frames the shared anatomy and diagnostic logic that link them; the detailed essentials live in the individual topic nodes.

Sub-topics

• Pleural Effusion
• Pleural Infection and Empyema
• Pneumothorax

Core questions

• Is the pleural abnormality fluid, air, pus, or solid tissue?
• If fluid, is it a transudate or an exudate, and what process explains it?
• Is the pleural process a primary pleural disorder or a manifestation of systemic or pulmonary disease?
• What is the role of imaging, pleural fluid analysis, and tissue sampling in reaching a diagnosis?

Key concepts

• Visceral and parietal pleura
• Pleural space and pleural fluid turnover
• Transudate versus exudate (Light's criteria)
• Pleural effusion
• Pneumothorax
• Empyema and pleural infection
• Pleural malignancy and mesothelioma
• Thoracentesis and chest drainage

Mechanisms

The pleural space normally holds only a few millilitres of fluid, maintained by a balance between filtration from systemic pleural vessels and drainage through parietal pleural lymphatics, with a small negative pressure that keeps the lung apposed to the chest wall. Pleural disease arises when this balance is disturbed: increased hydrostatic or decreased oncotic pressure produces a transudative effusion; increased capillary permeability or impaired lymphatic drainage from inflammation, infection, or malignancy produces an exudative effusion; a breach of either pleural surface admits air and produces pneumothorax; and neoplastic transformation of mesothelial cells gives rise to mesothelioma. Light's criteria operationalise the transudate-exudate distinction using pleural-fluid-to-serum protein and LDH ratios.

Clinical relevance

Pleural disease is encountered across respiratory, infectious, oncological, and cardiac practice, and the same investigative sequence — imaging, pleural fluid sampling, and where needed pleural biopsy — recurs throughout. This entry describes how pleural disorders are conceptualised and categorised for reference and education; it does not provide diagnostic thresholds or treatment instructions for individual patients.

Epidemiology

Pleural effusion alone affects large numbers of patients each year, with congestive heart failure, pneumonia, and malignancy among the commonest causes; pneumothorax, pleural infection, and mesothelioma are described in their respective topic nodes. The distribution of causes varies with the underlying population and the prevalence of heart failure, infection, cancer, and asbestos exposure.

History

Examination of pleural fluid to separate transudates from exudates was placed on a quantitative footing by Light and colleagues in 1972, whose criteria remain a reference point in the evaluation of effusions. Subsequent decades saw the consolidation of imaging (including thoracic ultrasound), minimally invasive sampling, and society guidelines that now structure the approach to each of the major pleural disorders.

Key figures

• Richard W. Light
• David Feller-Kopman

Seminal works

• light-1972
• feller-kopman-2018

Frequently asked questions

What are the main categories of pleural disease?

They are usefully grouped by what abnormally occupies the pleural space: fluid (pleural effusion), air (pneumothorax), pus or infection (pleural infection and empyema), and tumour (notably mesothelioma). Each is treated as a separate topic.

Why is the transudate-versus-exudate distinction so central?

Classifying a pleural effusion as a transudate or an exudate narrows the list of likely causes and directs further investigation; Light's criteria are the classic way this distinction is made.