Pneumothorax is best described as what?

• A. Air in the abdominal cavity
• B. Blood in the pleural cavity
• C. Air in the pleural cavity
• D. Fluid in the peritoneal cavity

Answer: (C)

Pneumothorax is air in the pleural space between the lung and the chest wall, which disrupts the normal negative pressure that keeps the lung expanded. As air collects there, the lung may partially or fully collapse, leading to breathing difficulty and chest pain. The other situations describe different problems: blood in the pleural cavity is a hemothorax, and fluid in the peritoneal cavity is ascites; air in the abdominal cavity would be pneumoperitoneum.