What does pleural effusion refer to?

Pleural effusion refers to an abnormal fluid accumulation in the pleural space, which is the thin fluid-filled area between the two layers of the pleura that surround the lungs. This condition can occur due to various reasons, including inflammation, infection, or malignancy, leading to the buildup of fluid that can impair breathing by limiting lung expansion.

The presence of excess fluid in the pleural space can result in symptoms such as shortness of breath, chest pain, and cough. Identifying the nature and cause of a pleural effusion is essential for determining the appropriate treatment, which may involve draining the fluid or addressing the underlying condition.

Other options describe different conditions related to the pleura or lung mechanics. Air in the pleural cavity refers specifically to a pneumothorax, while the accumulation of pus in the pleural cavity is known as empyema. The collapse of lung tissue is referred to as atelectasis, which involves the lung unable to expand fully. Therefore, option C accurately captures the correct definition of pleural effusion.