It is the accumulation of fluid in between the parietal and visceral pleura, called pleural cavity.
It can occur by itself or can be the result of surrounding parenchymal disease.
Pleural fluid is classified as a transudate or exudate based on modified Light’s criteria.
Pleural fluid is considered an exudative effusion if at least one of the criteria are met.
Pleural fluid protein/serum protein ratio 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 limits of normal laboratory value for serum LDH.
Common causes of transudates include conditions which alter the hydrostatic or oncotic pressures in the pleural space like congestive left heart failure, nephrotic syndrome, liver cirrhosis, hypoalbuminemia leading to malnutrition and with the initiation of peritoneal dialysis.
Common causes of exudates include pulmonary infections like pneumonia or tuberculosis, malignancy, inflammatory disorders like pancreatitis, lupus, rheumatoid arthritis, post-cardiac injury syndrome, chylothorax (due to lymphatic obstruction), hemothorax (blood in pleural space) and benign asbestos pleural effusion.
A patient with pleural effusion can be asymptomatic or can present with exertional breathlessness depending on the impairment of thoracic excursion.
Patient with active pleural inflammation called pleurisy complains of sharp, severe, localized crescendo/ decrescendo pain with breathing or a cough.
The physical examination can be subtle. In large effusion, there will be the fullness of intercostal spaces, and dullness on percussion on that side.
Auscultation reveals decreased breath sounds and decreased tactile and vocal fremitus.
Egophony is most pronounced at the superior aspect of the effusion.
Pleural rub, often mistaken for coarse crackles can be heard during active pleurisy without any effusion.
