What is the pathologic mechanism most commonly responsible for malignant pleural effusion?

What is the pathologic mechanism most commonly responsible for malignant pleural effusion?

• A. Lymphatic Obstruction
• B. Increased Hydrostatic Pressure
• C. Inflammation Due to Infection
• D. Decreased Oncotic Pressure

Answer: (A)

Malignant pleural effusion most often arises because tumor cells invade or compress the pleural lymphatics, blocking drainage from the pleural space. When the lymphatic pathways are obstructed, fluid cannot be reabsorbed effectively, so it accumulates in the pleural cavity. This results in an exudative effusion that is rich in protein and often contains malignant cells on cytology. Why this stands out: increased hydrostatic pressure, seen in conditions like heart failure, tends to produce transudative effusions with low protein content; decreased oncotic pressure from hypoalbuminemia also favors transudates. Inflammation from infection can cause an exudative effusion, but the hallmark mechanism in malignancy is direct disruption or obstruction of pleural lymphatic drainage by tumor.

Malignant pleural effusion most often arises because tumor cells invade or compress the pleural lymphatics, blocking drainage from the pleural space. When the lymphatic pathways are obstructed, fluid cannot be reabsorbed effectively, so it accumulates in the pleural cavity. This results in an exudative effusion that is rich in protein and often contains malignant cells on cytology.

Why this stands out: increased hydrostatic pressure, seen in conditions like heart failure, tends to produce transudative effusions with low protein content; decreased oncotic pressure from hypoalbuminemia also favors transudates. Inflammation from infection can cause an exudative effusion, but the hallmark mechanism in malignancy is direct disruption or obstruction of pleural lymphatic drainage by tumor.