What is a pneumothorax?

A pneumothorax is defined as air trapped in the pleural space, which is the area between the lung and the chest wall. This condition can lead to the lung collapsing due to the pressure imbalance in that space. When air enters the pleural cavity, it can prevent the lung from expanding fully during inhalation, resulting in difficulty breathing and reduced oxygenation of the blood. Understanding this definition is critical for recognizing the symptoms and potential complications associated with pneumothorax, which can arise from various causes, including trauma or spontaneously without any apparent reason.

The other options describe different pathological conditions. Fluid accumulation in the lungs refers to pulmonary edema, which affects gas exchange rather than air presence in the pleural space. Inflammation of lung tissue pertains to conditions like pneumonia or bronchitis. Finally, while a pneumothorax can indeed be caused by chest trauma, it is not exclusively defined by trauma; thus, it is the presence of air in the pleural cavity that is the central characteristic of this condition.