What is the best imaging modality to visualize a loculated pleural effusion?

From the Guidelines

The best imaging modality to evaluate a loculated pleural effusion is ultrasound, as it provides excellent visualization of loculated fluid collections and can guide drainage procedures, as recommended by the most recent and highest quality study 1. When evaluating a loculated pleural effusion, it is essential to choose an imaging modality that can accurately visualize the fluid collection and guide management decisions.

• Ultrasound is a valuable point-of-care option, particularly for bedside evaluation and procedure guidance, with a sensitivity, specificity, and accuracy of about 84%, 100%, and 94%, respectively, comparable with, or better than, conventional chest radiography 1.
• The use of ultrasound may be beneficial to rule in but not to rule out or exclude an effusion, and it can also accurately quantify the volume of a pleural effusion 1.
• While CT scanning is also an excellent imaging modality, ultrasound is preferred for loculated pleural effusions due to its ability to guide drainage procedures and its portability, allowing for bedside imaging 1, 2.
• MRI, though sensitive, is rarely used for this purpose due to cost, availability, and longer acquisition times.
• For patients requiring drainage of loculated effusions, ultrasound guidance is recommended to ensure accurate placement of drainage catheters into the appropriate loculation, as it has been shown to decrease complications associated with drainage 1. Key points to consider when choosing an imaging modality for loculated pleural effusion include:
• The ability to accurately visualize the fluid collection and guide management decisions
• The portability and availability of the imaging modality
• The ability to guide drainage procedures
• The sensitivity, specificity, and accuracy of the imaging modality
• The potential complications associated with each imaging modality.

From the Research

Imaging Modalities for Loculated Pleural Effusion

The best imaging modality to visualize a loculated pleural effusion can be determined by considering the following factors:

• Ultrasound: + Has a high sensitivity in detecting pleural diseases, including multiloculated pleural effusion 3 + Can detect very small amounts of loculated pleural fluid, even 3 to 5 ml 4 + Allows for easy differentiation between loculated pleural fluid and pleural thickenings 4 + Is useful in guiding pleural procedures, such as thoracocentesis 4, 5
• CT Scan: + May not identify loculations within pleural effusions as effectively as ultrasound 3 + Is the modality of choice for further assessment of pleural disease, including characterizing pleural thickening and demonstrating homogeneity of pleural masses 5
• Chest X-ray: + Typically does not show loculations 3 + May demonstrate complete or near-complete opacification of a hemithorax, indicating the need for further imaging 3, 6
• Other Modalities: + MRI has specific utility for soft tissue abnormalities and may have a role in younger patients requiring follow-up serial imaging 5 + PET/CT may provide additional information in malignant pleural disease regarding prognosis and response to therapy 5

Comparison of Imaging Modalities

The choice of imaging modality depends on the specific clinical scenario and the availability of resources.

• Ultrasound is a valuable tool for detecting loculated pleural effusions, especially in critically ill patients 3, 6
• CT scan is useful for further assessment of pleural disease, but may not be as effective in identifying loculations 3, 5
• Chest X-ray is typically the initial investigation of choice, but may not provide sufficient information to diagnose loculated pleural effusion 3, 5