Pulmonary contusion is characterized by

• A. Lung bruise causing hypoxia and worsening over time
• B. Air in pleural space causing lung collapse
• C. A chest wall infection
• D. Fluid in the alveolar sacs

Answer: (A)

Pulmonary contusion is a bruise of the lung parenchyma from blunt chest trauma, causing rupture of small vessels and bleeding into the air spaces and interstitium. This alveolar hemorrhage and edema disrupt the alveolar–capillary barrier, impairing gas exchange and leading to hypoxemia that can worsen over the next several hours as the contusion edema develops. This pattern distinguishes it from other issues: a pneumothorax involves air in the pleural space causing lung collapse; a chest wall infection would present with infectious signs rather than a parenchymal bruise; and while edema can occur, the defining feature is the traumatic parenchymal hemorrhage and injury.