creation date: 2025-11-03 15:52
tags: Pathologies
Pleural Effusion
Background
Definitions
Pleural effusion refers to the abnormal accumulation of fluid within the pleural space.
Etiology
Causes of pleural effusion is divided by whether the effusion is a transudate or exudate. The criteria for assessing the effusion type is discussed below.
Transudative pleural effusion (watery) - conditions that alter hydrostatic/oncotic pressures:
- Left heart failure
- Nephrotic syndrome
- Liver cirrhosis
- Hypoalbuminemia
- Peritoneal dialysis
- Pulmonary embolism
Exudative pleural effusion (rich in cells/protein):
- Pulmonary infections (eg. pneumonia, tuberculosis)
- Malignancy
- Inflammatory disorders (eg. pancreatitis, lupus, rheumatoid arthritis)
- Post-cardiac injury syndrome
- Chylothorax
- Hemothorax
- Post-CABG
- Benign asbestos pleural effusion
- Pulmonary embolism
- Drug-induced (eg. methotrexate, amiodarone, phenytoin, dasatinib)
- Radiotherapy
- Esophageal rupture
- Ovarian hyperstimulation syndrome
Pathogenesis
The pleural space normally contain a thin layer of fluid that allows for the visceral and parietal pleural to slide over each other during inspiration and expiration, allowing for smooth lung movements.
The balance of fluid is determined by gravity, ventilatory motion, and hydrostatic and oncotic pressures. A normal amount of fluid is around 0.1-0.3 mL/kg and fluid is derived from blood vessels of the parietal plural surfaces through the hydrostatic pressure of the systemic vessels. Fluid is then reabsorbed through lymphatic vessel.
Accumulation of excess fluid can thus occur through excessive production or decreased absorption. Additionally, increased permeability of the pleural or pulmonary capillary can increase the volume of fluid entering the pleural cavity.
In cases of transudative effusions, the effusion arises due to changes in pressure or oncotic gradient dysequilibrium resulting in the movement of fluid. However, because capillary permeability is preserved, proteins do not shift.
With exudative effusions, increased permeability of the pleural or capillary results in movement of both fluid and the proteins within the fluid.
Clinical Presentation
Signs & Symptoms
Symptoms can vary from no discernible signs to exertional breathlessness. The correlation between effusion size and severity of symptom does not correlate.
Other associated signs and symptoms depend on the underlying cause. This can include:
- Cough
- Fever
- Systemic signs
- Hemodynamic changes
- Pleuritic pain (with pleural inflammation)
The appearance of pleural fluid can also be suggestive of the type of effusion:
- Watery - transudative
- Straw-coloured/cloudy - exudative
- Milky - lymphatic
History & Physical Exam
History and examination should be used to narrow the differential. This includes:
- Comorbid conditions involving the heart, liver, or kidney disease (effusion may be due to fluid overload)
- Signs and symptoms of pneumonia or tuberculosis
- Symptoms or risk factors for malignancy
- Drug and occupation history (eg. nitrofurantoin, amiodarone, ovarian stimulation therapy)
- Recent procedures (eg. central line insertion, urinary or biliary intervention)
- Potential extra-pleural sources (eg. urinary tract obstruction, ascites)
Risk factors
Diagnosis
Criteria
Diagnosis can be made with chest radiograph. This shows up as:
- Blunting of the costophrenic angle
- Meniscus sign
Point-of-care ultrasound can also rapidly diagnose an effusion and size.
Work-up
CT chest is not always necessary but is useful if:
- Etiology is not obvious
- Pleural effusion is complex and loculated
- Malignancy or other disease more apparent on CT is suspected
Thoracentesis can be used to remove pleural fluid via needle, needle over catheter, or small-bore catheter. The procedure involves removing fluid by guiding needle/tube over a rib (to avoid rib vasculature).
This can be used diagnostically or therapeutically. In cases of unclear etiology, diagnostic thoracentesis can be used to determine the nature of the pleural effusion:
Light’s criteria
The pleural fluid is assessed for:
- Quantitative ratio of pleural fluid lactate dehydrogenase (LDH) to serum LDH levels
- Ratio of pleural fluid protein to serum protein levels
The fluid is considered exudative effusion if:
- Pleural fluid protein/serum protein ratio of more than 0.5
- Pleural fluid LDH/serum LDH ratio of more than 0.6
- Pleural fluid LDH is more than two-thirds of the upper limit of the normal serum LDH value
The fluid is considered transudative if none of these criteria are met. Exudative effusions require further workup of the pleural fluid.
- Condition-specific markers may be indicated if conditions are suspected (eg. acid-fast bacilli if TB is suspected)
- Cytological testing may be necessary if malignant pleural effusion is suspected
- Invasive techniques such as needle biopsies or thoracoscopy may be necessary
Blood tests should include:
- CBC with differential
- Serum electrolytes, creatinine, urea
- Liver function tests and enzymes
- Albumin
- Lipase
- Cardiac enzymes
- D-dimer
Differential
The differential includes the various conditions that causes pleural effusion.
Red Flags / Complications
While pleural effusion is often manageable, it can lead to complications.
- Empyema - accumulation of infected fluid in pleural space
- Pleural thickening from fibrous adhesions
Management
Management consist treating the underlying cause.
In symptomatic patients, therapeutic pleural fluid drainage is recommended. In the settings of heart failure, thoracentesis is only indicated if diuretics do not work.