What causes exudative pleural effusion?

Exudative pleural effusion is characterized by the presence of high protein content, and it typically occurs as a result of increased capillary permeability. This increase in permeability can be triggered by various factors, including infection, malignancy, or inflammatory processes, leading to the accumulation of fluid rich in proteins and inflammatory cells within the pleural space.

When the blood vessel walls become more permeable, they allow not only fluid but also larger molecules, such as proteins, to escape into the pleural cavity. Conditions like pneumonia, tuberculosis, and certain cancers are common underlying causes of increased capillary permeability, resulting in an exudative effusion. This differentiates it from a transudative effusion, which is primarily related to systemic issues such as fluid overload or decreased oncotic pressure.

Understanding the pathological mechanisms behind pleural effusions is essential for accurate diagnosis and management. The other options do not directly cause exudative pleural effusions, as decreased hydrostatic pressure and increased oncotic pressure are more associated with transudative processes, while obstruction of lymphatic drainage might lead to other forms of effusion but does not specifically relate to the exudative type characterized by high protein content.