What is the most common cause of pleural effusions?

The most common cause of pleural effusions is left-sided heart failure. In cases of heart failure, especially when the left side of the heart is involved, there is an increase in hydrostatic pressure in the pulmonary circulation. This elevated pressure encourages fluid to leak from the capillaries into the pleural space, resulting in a pleural effusion.

While infections like pneumonia can lead to parapneumonic effusions, and malignancy can contribute to effusions due to either obstruction of lymphatic drainage or pleural invasion, these conditions are not as prevalent as heart failure in the general population. Additionally, tuberculosis can cause pleural effusions, but it is less common than heart failure-related effusions. Therefore, left-sided heart failure is typically recognized as the most frequent etiology of pleural effusions seen in clinical practice.