Final answer:
Malignant pleural effusions present with exudate, a protein-rich fluid indicating underlying conditions such as tumors or inflammation, distinguishing it from transudate.
Step-by-step explanation:
Malignant pleural effusions typically present with a type of fluid known as exudate upon thoracentesis. Exudate is a fluid rich in proteins and cellular elements that often results from inflammation or malignancy, which causes an increase in the permeability of the capillary walls adjacent to the pleura. In contrast to transudate, which is typically characterized by lower protein content and is more commonly associated with non-inflammatory conditions such as heart failure or cirrhosis, exudate suggests a more active process involving pleural inflammation or tumor involvement. Therefore, when thoracentesis yields exudative fluid, it implies an underlying condition, such as malignancy, pneumonia, or rheumatologic diseases.