Pleural Diseases

General Principles

  • The pleural lining is a serous membrane covering the lung parenchyma, chest wall, diaphragm, and mediastinum.
  • The presence of excess fluid or any amount of gas in the pleural space is abnormal.
  • 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 pleura of each lung is the pleural space, a potential space that contains a thin layer of fluid of approximately 10 mL in volume.
  • The parietal pleura secretes approximately 2400 mL of fluid daily, which is reabsorbed by the visceral pleura.1

Definition

  • A pleural effusion is an accumulation of >10 mL of fluid in the pleural space.
    • A hemothorax refers to a pleural effusion that mainly comprises blood.2
    • Chylothorax is a collection of chyle within the pleural space. Chyle is a milky fluid consisting of lymph and fat droplets.3
    • A parapneumonic effusion is fluid collection in the pleural space as a result of a pneumonia/consolidation or bronchiectasis. The three types of parapneumonic effusions include uncomplicated effusion, complicated effusion, and empyema.4,5
    • An empyema refers to infected fluid within the pleural space.
  • A pneumothorax is a collection of air in the pleural space.
    • Primary spontaneous pneumothorax occurs when the lung parenchyma is normal without any obvious underlying lung disease.6
    • Secondary spontaneous pneumothorax is a complication of underlying parenchymal lung disease.6
    • Sometimes if air is trapped in the pleural space under high pressure, a tension pneumothorax develops, which can be fatal if not recognized and treated.7,8

Epidemiology

  • More than one million cases of pleural effusion occur annually in the US.
  • It is estimated that malignant pleural effusion affects about 150,000 people a year in the US. Congestive heart failure and parapneumonic effusion are the predominant etiologies of pleural effusion in the US.5
  • Incidence of pneumothorax varies widely by gender, country, and race.

Etiology

  • Pleural effusions have a variety of causes and are listed below (Table 10-14).
    • Empyema is generally caused by extension of an infection of the lung or surrounding tissue.
      • Common microbial pathogens are S. aureus, Streptococcus species, H. influenza, and oral anaerobes.
      • Empyemas are frequently polymicrobial in cases where aspiration is suspected, commonly because of oral flora.
    • The three major grouped causes of chylothorax are malignancy (50% of cases),3,9 trauma (25%), and idiopathic (15%).10 Other rare causes such as LAM11 and trauma to thoracic duct account for 10%.
      • Seventy-five percent of chylous effusions associated with malignancy are due to lymphoma-related obstruction of pleural lymphatics preventing reabsorption of pleural fluid.3
      • Trauma as a causative factor of chylothorax includes any cardiothoracic surgical procedure. It may take 1–2 weeks postsurgery for the chylothorax to become apparent.
      • In a number of cases, chylothorax results from transdiaphragmatic leakage of chylous ascites.3 Causes of chylous ascites include nephrotic syndrome, hypothyroidism, and cirrhosis of the liver.3
    • Hemothorax may result from trauma or an iatrogenic etiology and are rarely spontaneous.2
    • Other causes of pleural effusion include heart failure, anasarca, and pulmonary embolism.
  • Secondary pneumothorax is often seen in chronic obstructive pulmonary disease, AIDS, CF, TB, P. jirovecii pneumonia, sarcoidosis, pulmonary fibrosis, asthma, Marfan disease, LAM, PLCH, trauma, or any cavitary or cystic lung disease.
Table 10-14: Causes of Pleural Effusion
  • Exudates
    • Infections
      • Bacteria
      • TB
      • Fungi
      • Parasites
      • Viruses
      • Mycoplasma
    • Neoplasms
      • Metastatic carcinoma
      • Lymphoma
      • Leukemia
      • Mesothelioma
      • Bronchogenic carcinoma
      • Chest wall tumors
    • Intra-abdominal disease/gastrointestinal
      • Abdominal surgery
      • Pancreatitis
      • Meigs syndrome
      • Intrahepatic abscess
      • Incarcerated diaphragmatic hernia
      • Subdiaphragmatic abscess
      • Esophageal rupture
      • Endoscopic variceal sclerotherapy
      • Hepatitis
    • Collagen vascular diseases/vasculitis
      • Systemic lupus erythematosus
      • Rheumatoid arthritis
      • Drug-induced lupus
      • Sjögren syndrome
      • Granulomatosis with polyangiitis
      • Eosinophilic granulomatosis with polyangiitis
      • Immunoblastic lymphadenopathy
    • Drug-induced pleural disease
      • Nitrofurantoin
      • Dantrolene
      • Methysergide
      • Bromocriptine
      • Procarbazine
      • Amiodarone
    • Pulmonary infarction secondary to thromboembolic disease
    • Miscellaneous
      • Dressler syndrome (postcardiac injury)
      • Sarcoidosis
      • Yellow nail syndrome
      • Trapped lung
      • Radiation therapy
      • Electrical burns
      • Iatrogenic injury
      • Ovarian hyperstimulation syndrome
      • Chronic atelectasis
      • Asbestos exposure
      • Familial Mediterranean fever
      • Urinoma
    • Idiopathic
    • Lipid laden
      • Chylous
      • Pseudochylous
    • Trauma
  • Transudates
    • Increased hydrostatic pressure
      • Congestive heart failure
      • Constrictive pericarditis
      • Superior vena caval obstruction
    • Decreased oncotic pressure
      • Cirrhosis
      • Nephrotic syndrome
      • Hypoalbuminemia
      • Peritoneal dialysis
    • Miscellaneous
      • Acute atelectasis
      • Subclavian catheter misplacement
      • Myxedema
      • Idiopathic

Pathophysiology

  • Pleural effusions can be categorized as transudates or exudates.
    • Transudates result primarily from passive fluid shifts that occur as a result of changes in the hydrostatic and/or oncotic pressures of the circulation.12
    • Exudates are indicative of an active pleural process such as inflammation of the pleura or underlying lung tissue.12
    • There are numerous causes of both transudates and exudates (Table 10-14).12
  • Primary spontaneous pneumothorax is thought to result from rupture of subpleural apical blebs, with no obvious preceding cause.13
  • Secondary pneumothorax results from rupture of pathologic lung architecture such as emphysematous bullae, cysts, or cavity formation.13

Risk Factors

  • Risk factors for pleural effusion reflect those of the underlying causative disease.
  • Primary spontaneous pneumothoraces are more common in tall, thin males and recur 50% of the time.
  • Marfan disease is associated with a primary spontaneous pneumothorax.13

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