Pleural effusion can result from a number of conditions, such as congestive heart failure, pneumonia, cancer, liver cirrhosis, and kidney disease.
The characteristics of the fluid depend on the underlying pathophysiologic mechanism. The fluid can be transudate, nonpurulent exudate, pus, blood, or chyle. Imaging studies are valuable in detecting and managing pleural effusions but not in accurately characterizing the biochemical nature of the fluid.
(Images of pleural effusion are shown below.)
Different imaging modalities can be used to diagnose and manage pleural disease. Findings on chest radiographs frequently confirm the presence of pleural effusion. Lateral decubitus projections enhance the sensitivity of conventional radiography.
Radiographic studies may not help in differentiating parenchymal processes from pleural processes. In addition, chest radiography is limited in evaluating the underlying etiology, as in differentiating benign disease from malignant pleural disease. Things to keep in mind when viewing a chest radiograph are an elevated hemidiaphragm and/or herniation, pleural thickening and/or fibrothorax, and subpleural fat.
Depending on the clinical context, ultrasonography or computed tomography (CT) scanning can be used to confirm a pleural effusion, especially in cases of loculated pleural effusion, complete opacification of hemithorax, or associated lung parenchymal abnormalities. Ultrasonography and CT scanning are more accurate than chest radiography in identifying the underlying etiology.
Both modalities can depict small effusions not visualized radiographically, and they are also used to guide interventional procedures to manage pleural effusions.
When viewing a CT scan, consider ascites and/or a subphrenic abscess.
Magnetic resonance imaging (MRI) is sometimes used to evaluate questionable CT findings; this modality has been reported to be more sensitive than CT scanning in differentiating benign from malignant causes of effusion.
FDG PET/CT can help differentiate malignant from benign pleural effusion. In one study, the sensitivities of CT imaging, FDG PET imaging, and FDG PET/CT integrated imaging in detecting malignant effusion were 75.0%, 91.7% and 93.5%, respectively.
Illustration of the chest, depicted in an upright position from the lateral aspect, shows a small effusion accumulating in the posterior costophrenic (CP) sulcus. Such small effusion cannot be detected on the frontal view but can be visible on the lateral radiographic view as blunting of the posterior CP angle (blue arrow on the next image).
Depiction of upright posteroanterior and lateral views of the chest (using overlay on actual normal radiograph) demonstrates the radiographic appearance of small left effusion as the one in the previous image. The blue arrow points to the effusion.
Illustration of the chest, depicted in an upright position from the lateral aspect, shows a larger small effusion accumulating in the lower chest, which can be detected on both lateral and frontal radiographic views. This effusion produces blunting of the lateral costophrenic angle on the frontal view.
Depiction of upright posteroanterior and lateral views of the chest (using overlay on actual normal radiograph) demonstrates the radiographic appearance of a larger small left effusion as the one in the previous image. The blue arrows point to the effusions.
Illustration of the chest, depicted in an upright position from the lateral aspect. This image shows a moderate effusion accumulating in the lower chest, which can be seen on both the frontal and lateral views as a dependent density with meniscal-shaped margin. Note that the actual fluid upper margin is horizontal. However, there is more fluid posteriorly and laterally due to the shape of the chest and recoil characteristics of the lung.
Illustration of upright posteroanterior and lateral views of the chest (using overlay on actual normal radiograph) demonstrates the radiographic appearance of a moderate left effusion, as in the previous image. The blue arrows point to the effusions.
Illustration of the chest, depicted in supine position from the lateral aspect, shows a moderate effusion accumulating in the posterior aspect of the chest. This layering effusion can be visible on the frontal view as an increased haziness. The vascular structures can be seen through this density.
Right lateral decubitus view in a 42-year-old woman with breast cancer confirms a right pleural effusion by demonstrating dependent layering of the fluid (arrows).
The advent of ultrasonography and CT scanning and the advances in drainage catheter design and interventional techniques have made imaging-guided management of intrathoracic collections a safe and effective alternative to traditional surgical therapy.
Ultrasonography or CT scanning can be used to guide thoracocentesis or catheter drainage of effusions.
Thoracocentesis is primarily performed under ultrasonographic rather than CT scan guidance. The use of image guidance improves the safety of the procedure and reduces the rate of complications. The small catheters are also associated with a complication rate lower than that associated with thoracotomy tubes.
Percutaneous thoracocentesis is reportedly most successful in effusions that are ultrasonographically anechoic, complex, or complex with movable septa, as compared with echogenic or complex effusions with fixed septa. However, in one study, no correlation was found between the ultrasonographic appearance of the effusion and the success of percutaneous chest drainage.
The success rate of radiologically guided drainage procedures is 72-88%.
In a study of 458 patients with pleural effusion who underwent either standard care using pleural puncture to draw fluid versus ultrasound-guided thoracentesis catheter drainage, successful drainage was higher with ultrasound-guided thoracentesis. Success rate with standard puncture was 84%, versus 100% with ultrasound-guided drainage.