What are the characteristics of a malignant pleural effusion?

Characteristics of a Malignant Pleural Effusion

Malignant pleural effusions are most commonly caused by lung cancer in men and breast cancer in women, together accounting for 50-65% of all cases, and typically indicate advanced disease with poor prognosis. 1

Etiology and Pathophysiology

• Lung cancer is the most common cause (25-52% of cases), followed by breast cancer (3-27%), lymphomas (12-22%), and other malignancies including ovarian and gastrointestinal cancers 1
• In 7-15% of malignant pleural effusions, no primary tumor is identified 1
• Pleural metastases typically arise from tumor emboli to the visceral pleural surface with secondary seeding to the parietal pleura 1
• Malignant effusions develop through several mechanisms:
  • Disruption or obstruction of lymphatic drainage by tumor cells 1
  • Direct tumor invasion of pleural surfaces 1
  • Hematogenous spread to parietal pleura 1
  • Local inflammatory changes causing increased capillary permeability 1
  • Tumor-induced angiogenesis and vascular invasion leading to hemorrhagic effusions 1
  • Vascular endothelial growth factor (VEGF) promoting angiogenesis and endothelial permeability 1

Clinical Presentation

• Dyspnea is the most common presenting symptom, occurring in more than half of cases 1
• Up to 25% of patients are asymptomatic at presentation, with effusions found incidentally 1
• Other symptoms include:
  • Chest pain (particularly in mesothelioma) - typically dull and aching rather than pleuritic 1
  • Constitutional symptoms - weight loss, anorexia, and malaise 1
  • Cough 1
  • Hemoptysis (suggests underlying lung cancer) 1
• Dyspnea results from multiple factors:
  • Reduced chest wall compliance 1
  • Depression of the ipsilateral diaphragm 1
  • Mediastinal shift 1
  • Reduction in lung volume 1
  • Neurogenic reflexes 1

Radiographic Features

• Most patients present with moderate to large effusions (500-2,000 ml) 1
• Malignancy is the most common cause of massive pleural effusions (occupying entire hemithorax), though only 10% present this way 1
• Absence of contralateral mediastinal shift in large effusions suggests:
  • Fixation of the mediastinum 1
  • Mainstem bronchus occlusion by tumor 1
  • Extensive pleural involvement (as seen in mesothelioma) 1
• CT scans help identify:
  • Small effusions not visible on chest radiographs 1
  • Mediastinal lymph node involvement 1
  • Underlying parenchymal disease 1
  • Pleural, pulmonary, or distant metastases 1
• Ultrasound can identify pleural lesions and guide thoracentesis 1

Pleural Fluid Characteristics

• Typically exudative, though rarely may have transudative characteristics 1
• May be serous, hemorrhagic, or chylous (especially in lymphoma) 1
• Diagnostic tests should include:
  • Cytology (positive in 31-55% of cases, lower yield in Hodgkin's disease) 1
  • Cell count and differential 1
  • Total protein 1
  • Lactate dehydrogenase (LDH) 1
  • Glucose 1
  • pH (low pH correlates with poor prognosis) 1
  • Amylase 1
• High pleural protein values (8-9 g/L) may suggest multiple myeloma 1
• Pleural fluid pH and glucose levels correlate with pleurodesis outcome and overall survival 1

Prognostic Implications

• Median survival ranges from 3-12 months after diagnosis, with lung cancer having the shortest survival period 2
• The presence of malignant cells in pleural fluid indicates poor prognosis 1
• In lung cancer, malignant pleural effusion upstages the disease to stage 4 3

Management Considerations

• Treatment is always palliative 4
• Main goals are evacuation of pleural fluid and prevention of re-accumulation 5
• Treatment options include:
  • Observation for asymptomatic effusions 1
  • Thoracentesis for symptomatic relief 1, 2
  • Chemical pleurodesis (talc is most common) 1, 2
  • Long-term indwelling pleural catheter 1, 2
  • Pleuroperitoneal shunting 1, 2
  • Thoracoscopy 1
• Treatment choice depends on patient's clinical status, underlying disease, and expected survival 2, 4

Special Considerations

• Paramalignant effusions are not directly caused by pleural metastases but are related to the primary tumor through mechanisms like:
  • Postobstructive pneumonia 1
  • Thoracic duct obstruction (chylothorax) 1
  • Pulmonary embolism 1
  • Transudative effusions from atelectasis or low oncotic pressure 1
  • Treatment-related causes (radiation therapy, chemotherapy drugs) 1
• Non-Hodgkin's lymphoma is the most common cause of chylothorax 1