Pleural effusion

The pleural space is a potential space between the outer surface of the lung, the visceral pleura, and the lining of the chest wall, the parietal pleura.

Pleural fluid normally results from the filtration of blood from high pressured vessels and is drained from the pleural space via lymphatics in the parietal pleura.

Fluid may originate from the lung interstitial space, intrathoracic lymphatics, intrathoracic blood vessels or the peritoneal cavity.


Differential diagnosis includes: malignancy, CHF, infections, and paramalignant effusions.

Normally this space is occupied by a small amount of fluid that aids to couple the lung to the chest wall and lubricates the interface of the visceral and parietal pleurae.

Refers to a collection of fluid in the pleural space and occurs when the rate of fluid formation exceeds the rate of absorption.

Classified as exudates or transudates: an exudates implies that a disease process is affecting the pleura directly, while an transudates indicates that the there is a remote process affecting hydrostatic and/or oncotic abnormalities increasing fluid formation or decreasing fluid absorption.

Cannot tell exudate from transudate by gross appearance.

Congestive heart failure is the most frequent cause of pleural effusions.

Typical effusion in heart failure is a transudate that resolves when failure is corrected.

CHF-36%, pneumonia-22%, malignancy-14%, pulmonary embolism-11%, other infections-7% and other causes 10%.

More than 80% of patients after coronary artery bypass surgery have pleural effusions.

May be seen in collagen disease, especially in patients with positive ANA.

No single test can absolutely distinguish exudates from transudate.

Less than 5% of neoplastic effusions are transudative.

Light’s criteria for exudate: pleural fluid to serum protein ratio>0.05, pleural fluid to serum LDH ratio >0.6, pleural fluid LDH >2/3 upper limit of normal for serum LDH.

Heffner’s criteria for exudate: pleural fluid protein >2.9 g/dL, pleural fluid LDH >0.45 upper limit of normal.

Malignancy is the most common cause of pleural effusion that occupies the entire hemithorax.

Massive pleural effusions can occur occasionally with bacterial or mycobacterial infections, congestive heart failure, trauma, cirrhosis, connective tissue disease, chylothorax, and ovarian hyperstimulation syndrome.

Bloody effusions favor a malignant diagnosis.

More than 150,000 malignant effusions diagnosed each year in the U.S.

Initial diagnostic approach includes thoracentesis to analyze the fluid for cytological, histological and biochemical analysis.

Pleural effusions due to rheumatoid pleuritis often have high LDH >10000L/L low pH ,7.30, and low glucose, <60 mg/dL.

Sensitivity of non invasive testing is diagnostic in 40-70% of cases.

May be associated with pleurisy chest pain when an inflamed pleura is present along with the effusion.

Dyspnea may be present when a restrictive ventilatory defect exists, and or the presence of compressive telecasts leading to hypoxemia.


It is commonly recommended microscopic examination of pleural fluid with Gram stain and microbiological study of pleiral fluid.

In patients with cancer and a low probability of pleural space infection routine microbiological studies are not recommended.


Clinically findings include dullness to percussion, decreased fremitus, decreased breath sound and egophony above the effusion.

PA and lateral chest x-ray is the pref2242ed radio imaging technique for diagnosis.

Costophrenic angle blunting and a meniscus sign are common findings when the effusion is small.

Lateral chest x-ray can detect as little as 175 ml of fluid.

PA films can detect 500 mL of fluid.

Portable chest c-rays are less sensitive in detecting pleural fluid than PA and lateral films and often do not demonstrate the meniscus sign.

Indications on portable chest x-rays include loss of diaphragm silhouette, and basilar opacity.

A lateral decubitus chest x-ray with the dependent side (the side of the effusion) down can quantitate the amount of fluid present, and to determine if the fluid is loculated or free flowing.

On lateral decubitus film measurement of the distance between the chest wall and the lower border of the lung of greater than 1 cm reflects the presence of significant fluid.

CT of the thorax can determine the amount of fluid present in the chest, can determine if the fluid is loculated and may be able to help determine the reason for the fluid accumulation, and can evaluate the pleural surface for abnormalities.

CT scan with contrast can determine if a pulmonary embolism is present as the cause of the effusion.

Ultrasound can be used to determine the presence of pleural effusion and help with therapeutic interventions such as thoracentesis, chest tube placement, and can determine if fluid is loculated or free flowing.

Ultrasound can be helpful to determine the presence of an associated empyema and can help determine if the fluid is an exudates or a transudate.


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