Causes of Massive Pleural Effusion
Malignancy is the most common cause of massive pleural effusion, defined as fluid occupying an entire hemithorax. 1
Primary Malignant Causes
Lung cancer is the leading malignant cause, accounting for 25-52% of all malignant pleural effusions based on cytology reviews. 1, 2 The mechanism involves tumor emboli to the visceral pleural surface with secondary parietal pleural seeding, direct tumor invasion, hematogenous spread, or lymphatic obstruction anywhere between the parietal pleura and mediastinal lymph nodes. 1
Breast cancer is the second most common malignancy, representing 3-27% of malignant effusions on cytology. 1, 2 Patients with disseminated breast cancer develop pleural effusions in 36-65% of cases. 1
Lymphoma accounts for approximately 12-22% of malignant pleural effusions. 1, 2
Mesothelioma characteristically presents with massive effusion and is associated with dull, aching chest pain rather than pleuritic pain. 1 These patients often show absence of contralateral mediastinal shift despite large effusion volume due to extensive pleural involvement. 1
Key Diagnostic Features in Massive Effusions
When encountering a massive pleural effusion, look for absence of mediastinal shift, which implies one of three critical findings: 1
- Mediastinal fixation by tumor
- Mainstem bronchus occlusion (usually squamous cell lung cancer)
- Extensive pleural involvement (as in mesothelioma)
Non-Malignant Causes
While malignancy dominates, other causes of massive effusion include:
Congestive heart failure can occasionally present with massive effusion, though this typically shows appropriate mediastinal shift and responds to diuresis. 2, 3
Empyema from complicated parapneumonic effusions may accumulate to massive volumes if untreated. 2, 3
Tuberculosis should be considered, particularly in endemic areas or immunocompromised patients, as it accounts for approximately 6% of all pleural effusions. 2
Clinical Pitfalls
Do not assume bilateral effusions exclude malignancy - while unilateral presentation is more common, malignant effusions can be bilateral. 1
Hemoptysis with pleural effusion is highly suggestive of bronchogenic carcinoma and should prompt urgent evaluation. 1
History of asbestos exposure identified on CT (pleural plaques) should raise suspicion for mesothelioma. 1
Immediate Diagnostic Approach
Perform diagnostic thoracentesis on any unilateral effusion or bilateral effusion with normal heart size. 1 Send pleural fluid for: nucleated cell count with differential, total protein, LDH, glucose, pH, and cytology. 1
Cytology has variable sensitivity (40-87% depending on tumor type), so negative cytology does not exclude malignancy. 1 If malignancy remains suspected after negative initial cytology, thoracoscopy should be considered. 2
Only 10% of malignant effusions present as massive on initial presentation, but when massive effusion is encountered, malignancy should be the primary consideration until proven otherwise. 1