Pleural effusion On Chest X ray

A 28 years old male came to radiology department for X-ray chest with history of breathlessness on exertion since 10 days.

X-ray chest  shows a large pleural effusion on left side, the trachea and mediastinum are pushed to the right, right lung field is clear.

Pleural effusion is the accumulation of fluid in the pleural space, i.e. between the visceral and parietal layers of pleura.
The fluid may be transude, exudate, blood, chyle or rarely bile.
Pleural fluid casts a shadow of the density of water on the chest radiograph. The most dependent recess of the pleura is the posterior costophrenic angle. A small effusion will, therefore, tend to collect posteriorly; however, a lateral decubitus view is the most sensitive film to detect small quantity of free pleural effusion (as small as 50 ml). 100–200 ml of pleural fluid is required to be seen above the dome of the diaphragm on frontal chest radiograph. As more fluid is accumulated, a homogeneous opacity spreads upwards, obscuring the lung base. Typically this opacity has a fairly well-defined, concave upper edge , which is higher laterally and obscures the diaphragmatic shadow. Frequently the fluid will track into the pleural fissures.
A massive effusion may cause complete radiopacity of a hemithorax. The underlying lung will retract
towards its hilum, and the space occupying effect of the effusion will push the mediastinum towards the opposite side.

USG chest confirms the presence or absence of the pleural fluid; it also shows the septations within the pleural fluid with or without solid component within the lesion. USG helps in guiding aspiration of pleural fluid. CT scan is the most sensitive modality for detection of presence of minimal fluid. It allows distinction between free and loculated fluid showing its extent and localization.

Clinical Discussion: Large pleural effusion often presents with shortness of breath, dyspnea, sharp chest pain worsening with a deep inspiration, cough and symptoms of underlying cause.
Small effusions go unnoticed many times. In large effusion there are clinical signs such as decreased movement of chest on affected side, stony dullness on percussion over the fluid, diminished
breath sounds, decreased resonance and fremitus and pleural friction rub.
Pleural effusion is either transudate or exudates.

• Transudative effusion is formed when fluid leaks from blood vessels into the pleural cavity such as in congestive cardiac failure, nephritic syndrome and hepatic cirrhosis.
• Exudative effusion is caused by the inflammation of pleura itself and is often due to lung pathology such as pneumonia, tuberculosis, lung malignancy. 

Whenever pleural effusion is diagnosed underlying cause should be explored to reduce further morbidity.

Treatment: Therapeutic aspiration is sufficient in small effusion. Large effusions require insertion of intercostal drainage tube. In any case the underlying cause should be treated to prevent recurrence. Thoracocentesis may be needed in malignant effusion.