Causes of paramalignant pleural effusions
| Cause | Comment |
| Local effects of tumour | |
| Lymphatic obstruction | Predominant mechanism for pleural fluid accumulation |
| Bronchial obstruction with pneumonia | Paraneumonic effusion; does not exclude operability in lung cancer |
| Bronchial obstruction with atelectasis | Transudate; does not exclude operability in lung cancer |
| Trapped lung | Transudate; due to extensive tumour involvement of visceral pleura |
| Chylothorax | Disruption of thoracic duct; lymphoma most common cause |
| Superior vena cava syndrome | Transudate; due to increased systemic venous pressure |
| Systemic effects of tumour | |
| Pulmonary embolism | Hypercoagulable state |
| Hypoalburninemia | Serum albumin <1.5 g·dL−1; associated with anasarca |
| Complications of therapy | |
| Radiation therapy | |
| Early | Pleuritis 6 weeks to 6 months after radiation completed |
| Late | Fibrosis of mediastinum |
| Constrictive perficarditis | |
| Vena caval obstruction | |
| Chemotherapy | |
| Methotrexate | Pleuritis or effustion; with or without blood eosinophilia |
| Procarbazine | Blood eosinophilia; fever and chills |
| Cyclophosphamide | Pleuropericarditis |
| Mitomycin/bleomycin | In association with interstitial disease |