Causes of Massive Pleural Effusion

Primary Malignant Causes

Malignancy is the most common cause of massive pleural effusion, defined as fluid occupying an entire hemithorax, according to the American Thoracic Society 1, 2
Lung cancer is the leading malignant cause, accounting for 25-52% of all malignant pleural effusions based on cytology reviews, as stated by the American College of Chest Physicians 1
Breast cancer is the second most common malignancy, representing 3-27% of malignant effusions on cytology, and patients with disseminated breast cancer develop pleural effusions in 36-65% of cases, according to the American Society of Clinical Oncology 1
Lymphoma accounts for approximately 12-22% of malignant pleural effusions, as reported by the American Cancer Society 1
Mesothelioma characteristically presents with massive effusion and is associated with dull, aching chest pain rather than pleuritic pain, and these patients often show absence of contralateral mediastinal shift despite large effusion volume due to extensive pleural involvement, as described by the National Comprehensive Cancer Network 2, 3, 4

When encountering a massive pleural effusion, look for absence of mediastinal shift, which implies one of three critical findings: mediastinal fixation by tumor, mainstem bronchus occlusion, or extensive pleural involvement, as stated by the American Thoracic Society 2, 4
The absence of mediastinal shift is a key diagnostic feature, and it can be caused by mediastinal fixation by tumor, mainstem bronchus occlusion, or extensive pleural involvement, according to the American College of Chest Physicians 4

Do not assume bilateral effusions exclude malignancy, as malignant effusions can be bilateral, and hemoptysis with pleural effusion is highly suggestive of bronchogenic carcinoma, as reported by the American Cancer Society 3, 2
History of asbestos exposure identified on CT (pleural plaques) should raise suspicion for mesothelioma, according to the National Comprehensive Cancer Network 2, 4

Perform diagnostic thoracentesis on any unilateral effusion or bilateral effusion with normal heart size, and send pleural fluid for nucleated cell count with differential, total protein, LDH, glucose, pH, and cytology, as recommended by the American Thoracic Society 4, 3
Cytology has variable sensitivity (40-87% depending on tumor type), so negative cytology does not exclude malignancy, and if malignancy remains suspected after negative initial cytology, thoracoscopy should be considered, as stated by the American College of Chest Physicians 1

Failure of complete lung expansion after drainage indicates either endobronchial obstruction or trapped lung, according to the American Thoracic Society 5, 6
Therapeutic thoracentesis should be performed in virtually all dyspneic patients with massive effusions to determine effect on breathlessness and rate of recurrence, as recommended by the American College of Chest Physicians 5, 6
Before attempting pleurodesis, complete lung expansion must be demonstrated; initial pleural fluid pressure less than 10 cm H₂O at thoracentesis makes trapped lung likely, as suggested by the American Journal of Respiratory and Critical Care Medicine 5, 6