Alexander C. Chen
Daniel J. Brown
The pleural lining is a serous membrane covering the lung parenchyma, chest wall, diaphragm, and mediastinum.
The pleural membrane covering the surface of the lung is known as the visceral pleura, the parietal pleura covers the remaining structures.
In between the visceral and parietal pleurae of each lung is the pleural space, a potential space that contains a thin layer of fluid of ∼10 mL in volume.
The parietal pleura secretes ∼2.5 L of fluid daily, which is reabsorbed by the visceral pleura.
A pleural effusion is >10 mL accumulation of fluid in the pleural space.
A hemothorax refers to a pleural effusion that is comprised mainly of blood.
Chylothorax is a collection of chyle within the pleural space.
A parapneumonic effusion is any effusion caused by bacterial pneumonia and occurs in about 40% of cases of bacterial pneumonia.1
Uncomplicated parapneumonic effusions do not require chest tube drainage for complete resolution and are presumed to be sterile.
Complicated parapneumonic effusions are accompanied by bacterial invasion of the pleural space and typically do require thoracostomy drainage, although occasionally may improve with antibiotic therapy alone.
Empyema simply refers to a complicated parapneumonic effusion with grossly purulent pleural fluid and is presumed to be infected even though cultures may not always be positive. On occasion, empyema may not be associated with a pneumonic process.
Primary spontaneous pneumothorax occurs when there is no obvious underlying lung disease.
Secondary spontaneous pneumothorax is a complication of underlying lung disease.
More than 1 million cases of pleural effusion occur annually in the United States.
Incidence of pneumothorax varies widely by gender, country, and race.4
Pleural effusions have a variety of causes (Table 23-1).
Empyema is generally caused by extension of an infection of the lung or surrounding tissue.
Common microbial pathogens are Staphylococcus aureus, Streptococcus species, and Haemophilus influenza.
Empyemas are frequently polymicrobial in cases where aspiration is suspected.
TABLE 23-1 CAUSES OF PLEURAL EFFUSION
Infection (viral, bacterial, mycobacterial, fungal, protozoal)
Chest wall tumors
Incarcerated diaphragmatic hernia
Endoscopic variceal sclerotherapy
Collagen vascular diseases
Systemic lupus erythematosus
Granulomatosis with polyangiitis
Pseudochylous (chyliform, i.e., cholesterol effusion)
Dressler syndrome (postcardiac injury)
Yellow nail syndrome
Ovarian hyperstimulation syndrome
Familial Mediterranean fever
Increased hydrostatic pressure
Superior vena cava obstruction
Decreased oncotic pressure
Subclavian catheter misplacement
The three major grouped causes of chylothorax are malignancy (50% of cases), trauma (25%), and idiopathic (15%). Other causes account for 10%.6
Seventy-five percent of chylous effusions related to malignancy are due to lymphomas related to obstruction of pleural lymphatics.
Trauma as a causative factor of chylothorax includes any cardiothoracic surgical procedure. It may take place 1–2 weeks postsurgery for the chylothorax to become apparent.
In a number of cases, chylothorax results from transdiaphragmatic leakage of chylous ascites. Causes of chylous ascites include nephrotic syndrome, hypothyroidism, and cirrhosis.
Pleural fluid protein to serum protein ratio of >0.5
Pleural fluid LDH to serum LDH ratio of >0.6
Pleural fluid LDH >2/3 serum upper limit of normal
Pleural fluid protein >2.9 g/dL
Pleural fluid cholesterol >45 mg/dL
Pleural fluid LDH >45% of upper limits of normal serum value
LDH, lactate dehydrogenase.
Hemothorax may result from trauma or iatrogenesis, and rarely can occur spontaneously.7
When the etiology for the effusion cannot be determined despite appropriate evaluation, a benign course is typical.8
Secondary pneumothorax is often seen in chronic obstructive pulmonary disease (COPD), AIDS, cystic fibrosis, TB, sarcoidosis, pulmonary fibrosis, asthma, Marfan disease, lymphangioleiomyomatosis, pulmonary Langerhans cell histiocytosis, trauma, or any disease with pulmonary cavity formation.4 Catamenial pneumothorax is a rare condition of spontaneous pneumothorax occurring in close proximity to menstruation and is often recurrent.4,5 It may also cause hemopneumothorax.
Transudates result primarily from passive fluid shifts that occur as a result of changes in the hydrostatic and oncotic pressures of the circulation.
Exudates imply an active pleural process such as inflammation of the pleura or underlying lung tissue.
There are numerous causes of both transudates and exudates (Table 23-1).