Pleural effusion, also known as fluid around the lungs, occurs when excess fluid builds up in the pleural space between the lungs and the chest wall. While pleural effusions are common and mostly non-cancerous, they can sometimes be a sign of an underlying cancer or spread of cancer to the pleural space, known as malignant pleural effusion.
What is Pleural Effusion?
The pleura is a thin membrane that lines the lungs and chest cavity. The pleural space between the two pleural membranes normally contains a small amount of lubricating fluid that allows the lungs to move smoothly against the chest wall during breathing. Pleural effusion occurs when excess fluid accumulates in this space.
There are two main types of pleural effusions:
- Transudative effusions – caused by disturbances in fluid dynamics, often due to congestive heart failure, kidney failure, or liver cirrhosis. These are usually non-cancerous.
- Exudative effusions – result from inflammation or diseases affecting the pleural surfaces, such as infection, autoimmune conditions, pulmonary embolism, or malignancy. These have a higher likelihood of being cancer-related.
Signs and Symptoms
The most common symptoms of pleural effusion include:
- Shortness of breath – especially when exerting oneself
- Dry cough
- Chest pain – usually dull and worse with deep breathing
- Feeling of chest heaviness or tightness
As the effusion worsens, symptoms may include:
- Inability to lie flat
- Fever and chills if infection is present
- Fatigue and weakness
Causes and Risk Factors
The causes of pleural effusion include:
- Infection – pneumonia, TB, fungal infections
- Autoimmune conditions – rheumatoid arthritis, lupus
- Heart failure – fluid buildup due to poor heart pumping function
- Kidney failure – fluid retention
- Liver cirrhosis – fluid retention and low albumin
- Pulmonary embolism – blood clots in lungs
- Medications – amiodarone, methotrexate, nitrofurantoin
- Trauma – rib fractures, esophageal rupture
- Malignancy – lung cancer, breast cancer, lymphoma, mesothelioma
Risk factors for developing malignant pleural effusions include:
- Age over 60 years
- History of cancer
- Smoking
- Asbestos exposure
- Bloody pleural fluid
How Cancer Causes Pleural Effusion
Cancer can cause pleural effusion through several mechanisms:
- Direct spread or seeding – Primary lung cancers or mesothelioma may directly invade the pleura and obstruct lymphatic drainage, causing fluid buildup.
- Metastasis – Breast, ovarian, gastrointestinal cancers may metastasize to the pleura and cause effusions.
- Decreased protein/albumin – Cancer can lead to decreased serum albumin levels, disrupting fluid balance and forcing fluid into the pleural space.
- Lymphoma – Lymphoma cells can infiltrate and obstruct pleural lymphatics.
Therefore, the discovery of malignant cells within a pleural effusion is a strong indicator that cancer is present somewhere in the body.
Diagnosing Pleural Effusions
Doctors use various tests to diagnose pleural effusions:
- Physical exam – decreased breath sounds, dullness to percussion over fluid
- Chest X-ray – will show fluid collection in pleural space
- CT scan – defines size and location of fluid pocket
- Thoracentesis – sampling fluid with a needle for analysis
Analysis of Pleural Fluid
Once pleural fluid is obtained via thoracentesis, analysis includes:
- Appearance – clear, yellow, bloody
- Protein, LDH, glucose, pH – help classify transudate vs exudate
- Cell count and differential – elevated white cells suggest infection
- Gram stain and culture – identify bacterial infection
- Cytology – checks for cancer cells
- Biomarkers – helps diagnose mesothelioma (eg, osteopontin)
This table summarizes the key differences between transudative and exudative pleural effusions:
| Parameter | Transudative | Exudative |
|---|---|---|
| Appearance | Clear, light yellow | Turbid, bloody |
| Protein | > 3 g/dL | |
| LDH | > 200 IU/L | |
| Glucose | Same as serum | Often lower than serum |
| pH | > 7.2 | Often |
Testing for Malignant Pleural Effusions
The following tests help diagnose malignant pleural effusions:
- Cytology – examining fluid samples for presence of cancer cells. Sensitivity around 60%.
- Biomarkers – elevated levels of mesothelin, osteopontin, or CEA may indicate malignancy.
- Medical imaging – CT scans may reveal lung or pleural masses, or enlarged lymph nodes.
- Pleural biopsy – done if cytology is negative but suspicion for cancer remains high based on imaging or clinical context.
If a primary lung cancer or mesothelioma is suspected, more invasive surgical biopsies may be performed, such as thoracoscopy or thoracotomy.
Treating Malignant Pleural Effusions
Treatment options for malignant pleural effusions include:
- Thoracentesis – draining fluid via chest tube to relieve symptoms. Often recurs so may require repeated procedures.
- Pleurodesis – instilling talc or other agents into the pleural space to cause inflammation and adhesion of the pleural layers, preventing fluid buildup.
- Shunt placement – implantable catheter system to continuously drain fluid into the abdomen or venous system.
- Systemic therapy – chemotherapy, targeted therapy, or immunotherapy to treat the underlying cancer.
The prognosis for malignant pleural effusion depends on the type of cancer and extent of disease progression at the time of diagnosis. Addressing the underlying cancer is key to long-term management.
Conclusion
In summary, the presence of cancer cells in pleural fluid signifies malignant pleural effusion. This condition should be suspected in patients with known cancer history and new onset of pleural effusion symptoms. Analysis of the fluid enables differentiating malignant from benign effusions. Cytology, biomarker studies and imaging help diagnose the primary cancer source. Draining procedures provide symptomatic relief while targeted anti-cancer therapies are needed to treat the root cause.
