Description

• Gas within the pleural space
• Primary spontaneous pneumothorax (PSP): This does not have a precipitating event in a person who does not have known lung disease.
• Secondary spontaneous pneumothorax (SSP): Associated with underlying lung disease. The most common: Chronic obstructive pulmonary disease (COPD), cystic fibrosis, Pneumocystic jiroveci infection, and tuberculosis (TB).

Epidemiology

• PSP: 7.4 and 1.2/100,000/year in men and women in the US, respectively.
• SSP: 6.3 and 2/100,000/year in men and women in the US, respectively.

• 70% of cases of SSP occur with COPD.
• Rupture of apical blebs
• 30% of patients with pneumocystic pneumonia develop SSP.
• 6% of all patients with cystic fibrosis will have an episode of SSP.
• 1–3% of patients hospitalized with TB

Risk Factors

• PSP: Smoking, family history, Marfan syndrome, homocystinuria, and thoracic endometriosis
• SSP:
  • Airway disease: COPD, asthma, cystic fibrosis, α₁-antitrypsin deficiency
  • Infection: Pneumocystis pneumonia, TB, necrotizing pneumonia
  • Malignancy: Lung cancer, synovial sarcoma
  • Connective tissue disorder: Marfan or Ehlers-Danlos syndromes, scleroderma, rheumatoid arthritis, ankylosing spondylitis, polymyositis/dermatomyositis
  • Interstitial lung disease: Sarcoidosis, idiopathic pulmonary fibrosis, histiocytosis X, lymphangioleiomyomatosis, esophageal rupture, bronchial obstruction/foreign body (also complications from scuba diving or a loss of airplane cabin pressure)
  • Traumatic pneumothorax:
    • Trauma (penetrating injury, broken rib, ruptured bronchus, perforated esophagus)
    • Iatrogenic/Postprocedure: Intubation, central line placement, liver biopsy, mechanical ventilation, thoracentesis, cardiopulmonary resuscitation
    • IV drug abusers (who attempt to access the internal jugular vein)

• PSP: A family history of autosomal-dominant, autosomal-recessive, polygenic, and X-linked recessive inheritance has been proposed.
• Birt-Hogg-Dubé syndrome: Autosomal-dominant, associated with lung cysts, benign skin tumor, renal cancer; the FLCN mutation has been mapped to chromosome 17p11.2
• Marfan syndrome: Some patients develop lung bullae, which predispose them to PSP. Genes implicated: Mutations in fibrillin-1 (FBN1), transforming growth factor-β receptor (TGFBR)

General Prevention

Patients should cease smoking and wear seatbelts while driving.

Pathophysiology

• Loss of negative intrapleural pressure, lung collapse
• Simple pneumothorax: Pleural pressure in the affected hemithorax remains subatmospheric and is only more positive than the pleural pressure in the contralateral hemithorax.
• Tension pneumothorax: Pleural pressure in the affected hemithorax exceeds atmospheric pressure, particularly during expiration.
• Open pneumothorax: Traumatic chest wall defect persists, and ambient air enters the pleural space during inspiration. Mediastinum shifts to the normal hemithorax, and the lung within the injured hemithorax remains collapsed. During expiration, the air exits the pleural space through the chest wall defect, and the mediastinum swings back toward the injured hemithorax.
• Pneumothorax ex vacuo: This is the result of rapid atelectasis, producing an abrupt decrease in the intrapleural pressure with the subsequent release of nitrogen from pleural capillaries.

Etiology

• Perforation of the visceral pleura and entry of gas from the lung; penetration of the chest wall, diaphragm, mediastinum, or esophagus
• Blunt thoracic trauma: Gas generated by microorganisms in an empyema
• Spontaneous rupture of pulmonary/subpleural bleb into pleural space
• Rupture of large subpleural cysts caused by subpleural necrosis is the cause of most SSP in patients with Pneumocystic jiroveci.
• Cystic fibrosis: Rupture of apical subpleural cysts, coinfection with Pseudomonas aeruginosa, Burkholderia cepacia complex, or Aspergillus spp., or a prior episode of massive hemoptysis
• TB: Rupture of a tuberculous cavity into the pleural space
• Pulmonary barotrauma: 10% on mechanical ventilation

Commonly Associated Conditions

See “Risk Factors.”