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[Conditions](https://durgical.com/en/conditions/) · [Chest](https://durgical.com/en/anatomy/region/chest/)

# Pleural effusion

A pleural effusion is fluid collected between the lung and the chest wall; it is a sign of another disease, such as heart failure, infection or cancer.

Updated 2026-10-29

## Structures involved

Tap one to see what it is and open it in 3D.

- [Pleura](https://durgical.com/en/anatomy/pleura/)
- [Right lower lobe](https://durgical.com/en/anatomy/inferior-lobe-of-right-lung/)
- [Left lower lobe](https://durgical.com/en/anatomy/inferior-lobe-of-left-lung/)
- [Diaphragm](https://durgical.com/en/anatomy/diaphragm/)
- [Thoracic duct](https://durgical.com/en/anatomy/thoracic-duct/)
- [Intercostal nerves](https://durgical.com/en/anatomy/intercostal-nerves/)

## In biochemistry

- [Adenosine deaminase (ADA)](https://durgical.com/en/biochemistry/enzymes/adenosine-deaminase/)

## In histology

- [Serous membranes: pleura and peritoneum](https://durgical.com/en/histology/serous-membranes-pleura-and-peritoneum/)

## In the clinical exam

- [Chest palpation: expansion and tactile fremitus](https://durgical.com/en/clinical-exam/chest-palpation-expansion-and-tactile-fremitus/)
- [Chest percussion: resonance, dullness and hyperresonance](https://durgical.com/en/clinical-exam/chest-percussion-resonance-dullness-and-hyperresonance/)
- [Lung auscultation: normal breath sounds](https://durgical.com/en/clinical-exam/lung-auscultation-normal-breath-sounds/)
- [Voice sounds: bronchophony, egophony and whispered pectoriloquy](https://durgical.com/en/clinical-exam/voice-sounds-bronchophony-egophony-and-whispered-pectoriloquy/)
- [The pleuropulmonary syndromes: the comparison table to know](https://durgical.com/en/clinical-exam/the-pleuropulmonary-syndromes-the-comparison-table-to-know/)
- [Pleural effusion syndrome](https://durgical.com/en/clinical-exam/pleural-effusion-syndrome/)
- [Atelectasis syndrome](https://durgical.com/en/clinical-exam/atelectasis-syndrome/)

## In physiology

- [Pleural fluid: formation and drainage](https://durgical.com/en/physiology/pleural-fluid-formation-and-drainage/)

## Why it happens

- [Edema and effusions: the four mechanisms](https://durgical.com/en/general-pathology/edema-and-effusions-the-four-mechanisms/)
- [Pulmonary thromboembolism: where it comes from and what it does](https://durgical.com/en/general-pathology/pulmonary-thromboembolism-where-it-comes-from-and-what-it-does/)
- [Vascular changes in acute inflammation: vasodilation, leakage, exudate vs transudate](https://durgical.com/en/general-pathology/vascular-changes-in-acute-inflammation-vasodilation-leakage-exudate-vs-transudat/)
- [Starling forces at the capillary](https://durgical.com/en/physiology/starling-forces-at-the-capillary/)

## What it is

Abnormal collection of fluid in the pleural space, between the parietal and visceral [pleura](https://durgical.com/en/anatomy/pleura/). It is a sign of an underlying disease rather than a diagnosis in itself.

## Who gets it

Very common in hospital practice. Heart failure is the most frequent cause of transudates; pneumonia and cancer are leading causes of exudates. In Colombia and Latin America tuberculosis remains an important cause of lymphocytic exudates in young adults.

## Causes

- Transudate: heart failure, cirrhosis, nephrotic syndrome, hypoalbuminaemia
- Exudate: pneumonia (parapneumonic, empyema), tuberculosis, cancer
- Pulmonary embolism
- Autoimmune disease (lupus, rheumatoid arthritis)
- Pancreatitis and subdiaphragmatic abscess
- Chylothorax from [thoracic duct](https://durgical.com/en/anatomy/thoracic-duct/) injury; haemothorax after trauma

## Risk factors

- Heart, [liver](https://durgical.com/en/anatomy/liver/) or [kidney](https://durgical.com/en/anatomy/kidney/) failure
- Pneumonia
- Cancer, especially lung and breast cancer and lymphoma
- Tuberculosis exposure
- Chest trauma or surgery

## Pathophysiology

Fluid forms when filtration into the pleural space exceeds lymphatic drainage. Transudates result from raised hydrostatic or reduced oncotic pressure with intact pleura; exudates result from inflammation, infection or tumour that increases capillary permeability or blocks lymphatics.

## Classification

- Transudate vs exudate (Light's criteria)
- Parapneumonic: simple, complicated, empyema
- Malignant
- Special types: haemothorax, chylothorax

## Symptoms and signs

- Breathlessness, depending on size and speed
- Pleuritic chest pain (in inflammatory causes)
- Dry cough
- Dullness to percussion over the fluid
- Reduced breath sounds and tactile fremitus
- Signs of the cause: fever, oedema, weight loss

## Red flags

- Fever with effusion (possible empyema)
- Massive effusion with mediastinal shift
- Breathlessness at rest or hypoxaemia
- Bloody fluid after trauma (haemothorax)
- Weight loss or a history of cancer

## Diagnosis

**Clinical**
Dullness and reduced breath sounds at the base; history points to the cause. Bilateral effusions with heart failure often need no tap.

**Tests**
Diagnostic thoracentesis: protein and LDH compared with serum (Light's criteria: an exudate meets at least one), pH, glucose, cell count, Gram stain and culture, cytology, and adenosine deaminase when TB is suspected.

**Imaging**
[Chest](https://durgical.com/en/anatomy/region/chest/) X-ray shows blunting of the costodiaphragmatic angle or a meniscus. Ultrasound detects small volumes, shows septations and guides the tap; CT looks for the cause.

## Differential diagnosis

- Lobar collapse or consolidation
- Pleural thickening
- Raised hemidiaphragm
- Pleural tumour (mesothelioma)

## Goal of treatment

Find and treat the cause, relieve breathlessness and drain infected or rapidly reaccumulating fluid to prevent a trapped lung.

## Treatment

**Medical**
Treatment of the cause: diuretics for heart failure, antibiotics for parapneumonic effusion, antituberculosis therapy for pleural TB.

**Procedure**
Therapeutic thoracentesis to relieve breathlessness from large effusions.

**Procedure**
Chest drain for empyema or complicated parapneumonic effusion; intrapleural fibrinolytic therapy in selected cases.

**Surgical**
Recurrent malignant effusion: pleurodesis or an indwelling pleural catheter; surgical decortication for organised empyema.

## Complications

- Empyema
- Trapped lung and pleural fibrosis
- Re-expansion pulmonary oedema after large drainage
- Pneumothorax from thoracentesis

## Prognosis

Depends on the cause: transudates improve with treatment of heart, liver or kidney disease; malignant effusion indicates advanced cancer with limited survival.

## Test yourself

Think of the answer, then tap the question to see it.

## What do Light's criteria compare to decide that a pleural effusion is an exudate?

Pleural fluid protein and LDH with serum values; meeting any one criterion classifies it as an exudate.

## What is the most common cause of a transudative pleural effusion?

Congestive heart failure.

## Which pleural fluid finding supports tuberculous pleurisy?

A lymphocyte-predominant exudate with raised adenosine deaminase (ADA).

## Which pleural fluid findings suggest a complicated parapneumonic effusion needing drainage?

Frank pus, a positive Gram stain or culture, or low pH and low glucose.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/conditions/pleural-effusion/)

## Related conditions

- [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/)
- [Pulmonary tuberculosis](https://durgical.com/en/conditions/pulmonary-tuberculosis/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)
- [Pulmonary embolism](https://durgical.com/en/conditions/pulmonary-embolism/)
- [Amoebic liver abscess](https://durgical.com/en/conditions/amoebic-liver-abscess/)
- [Pneumothorax](https://durgical.com/en/conditions/pneumothorax/)
- [Lung cancer](https://durgical.com/en/conditions/lung-cancer/)
- [Haemothorax](https://durgical.com/en/conditions/haemothorax/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Pleural Effusion](https://www.ncbi.nlm.nih.gov/books/NBK448189/) (StatPearls (NCBI Bookshelf), 2024).

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Source: https://durgical.com/en/conditions/pleural-effusion/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/pleural-effusion/