Subcutaneous emphysema can have which of the following as its causes?

• A. Bacterial infection
• B. Pulmonary edema
• C. Allergic reaction
• D. The same causes as mediastinal emphysema

Answer: (D)

Subcutaneous emphysema happens when air escapes from the lungs or airways and tracks into the soft tissues under the skin. The air often reaches these tissues because it first leaks into the mediastinum (pneumomediastinum) or pleural space, then dissects along tissue planes up to the neck and chest. Because air follows the same routes regardless of the initial leak, the causes that lead to air in the mediastinum are the same ones that can cause subcutaneous emphysema. So trauma to the chest, pneumothorax, alveolar rupture from barotrauma or disease, and injuries or procedures that let air escape into the chest are all potential triggers. While gas-forming infections can produce tissue gas in some settings, the broad, typical causes for subcutaneous emphysema align with those for mediastinal emphysema, making the statement that they share causes the most accurate. Allergic reactions do not create an air leak.