Malignant Pleural Effusion

Malignant pleural effusion (MPE) means that cancer cells have invaded the pleural space.  This often leads to fluid accumulation around the lungs. This indicates advanced disease and negatively impacts patient prognosis.  Imaging plays an important role in diagnosing and managing MPE.

Key Imaging Features of Malignant Pleural Effusion

Chest X-ray Findings in Malignant Pleural Effusion

Chest X-ray (CXR) is often the first imaging test performed when MPE is suspected. The key findings include:

Unilateral or bilateral pleural effusion.  While MPE is more commonly unilateral, it can be bilateral in some cases.

Meniscus sign: The characteristic upward curving of fluid along the chest wall.

Mediastinal shift: If the effusion is large enough, it may push the mediastinum to the opposite side. However, in malignant cases with lung entrapment, the mediastinum may remain central.

Pleural thickening or nodularity: suggests malignant involvement rather than a simple transudative effusion.

Ultrasound for Malignant Pleural Effusion

Point-of-care ultrasound (POCUS) is a valuable tool for evaluating pleural effusions in real time. It helps in both diagnosis and procedural guidance.

Anechoic or complex fluid: simple effusions are anechoic (black on ultrasound), while malignant effusions may appear complex with internal septations.

Pleural thickening : a concerning sign for malignancy.

Diaphragmatic nodularity: strongly suggests metastatic disease.

Sonographic guidance for thoracentesis: ultrasound helps identify safe needle insertion sites for fluid drainage.

CT Scan Features of Malignant Pleural Effusion

CT imaging provides a more detailed assessment of pleural involvement and underlying malignancy.

Large-volume effusion with pleural thickening- malignant effusions often present with irregular pleural thickening rather than smooth layering.

Nodular pleural deposits- discrete pleural nodules suggest metastatic disease.

Mediastinal and diaphragmatic pleural involvement- malignancy frequently spreads along these surfaces.

Underlying lung mass or lymphadenopathy- helps identify the primary tumor, especially in lung cancer or mesothelioma.

Collapsed lung with fluid loculations- suggests lung entrapment, common in malignancy.

MRI in Malignant Pleural Effusion

While not commonly used as the first-line imaging modality, MRI can help differentiate malignant from benign pleural disease.

PET-CT for Malignant Pleural Effusion

PET-CT plays a role in staging and assessing metabolic activity in pleural malignancy.

Hypermetabolic pleural nodules- increased FDG uptake strongly suggests malignancy.

Lymph node involvement- helps determine disease extent.

Differentiation from benign effusions- benign effusions generally show no FDG uptake, whereas malignant ones may have high uptake.

Differentiating Malignant from Benign Pleural Effusions on Imaging

Not all pleural effusions are malignant. Imaging features that raise suspicion for malignancy include:

Pleural nodularity or thickening

Mediastinal pleural involvement

Loculated or complex effusion

Absence of significant shifting with position changes

Associated lung masses or lymphadenopathy

Conversely, benign effusions tend to be free-flowing and lack pleural enhancement or nodularity.

Role of Imaging-Guided Thoracentesis and Biopsy

Once imaging suggests malignant pleural effusion, fluid aspiration (thoracentesis) is performed to confirm malignancy.

Ultrasound-guided thoracentesis- reduces complication risk and increases success rate.

CT-guided pleural biopsy- useful when pleural nodularity or thickening is present.

Conclusion

Imaging plays an important role in the diagnosis and management of malignant pleural effusion. Chest X-ray provides the initial assesment, ultrasound assists in fluid evaluation and drainage, CT helps in detecting pleural malignancy, and PET-CT is used for staging. Recognizing the key imaging features of MPE allows for early diagnosis and appropriate management.

References

1.https://www.thoracic.org/patients/patient-resources/resources/malignant-pleural-effusions.pdf

2.https://www.ncbi.nlm.nih.gov/books/NBK574541/

3.https://www.sciencedirect.com/science/article/pii/S2659663624000523