What are the causes of a right-sided massive pleural effusion?

Causes of Right-Sided Massive Pleural Effusion

Malignancy is the most common cause of massive pleural effusion (occupying an entire hemithorax), accounting for 55% of cases, followed by complicated parapneumonic effusion/empyema (22%) and tuberculosis (12%). 1, 2

Primary Etiologies in Order of Frequency

Malignant Causes (55% of massive effusions)

• Lung cancer is the leading malignant cause, representing 25-52% of all malignant pleural effusions based on cytology reviews 1
• Breast cancer is the second most common malignancy, accounting for 3-27% of malignant effusions, with 36-65% of patients with disseminated breast cancer developing pleural effusions 1
• Lymphoma accounts for approximately 12-22% of malignant pleural effusions 1
• Mesothelioma characteristically presents with massive effusion and is associated with dull, aching chest pain rather than pleuritic pain 1

Infectious Causes (22% of massive effusions)

• Complicated parapneumonic effusion and empyema represent the second most common cause of massive effusions 2
• In IV drug users, Staphylococcus aureus is particularly common and requires broad-spectrum empirical coverage 3
• Bacterial pneumonia can progress through exudative, fibropurulent, and organized stages requiring both antibiotics and drainage 3

Tuberculosis (12% of massive effusions)

• Tuberculous pleurisy is the third most common cause of large and massive effusions 2
• This should be considered especially in high-prevalence regions 4

Critical Diagnostic Features Specific to Massive Effusions

Absence of Mediastinal Shift

When encountering a massive pleural effusion without contralateral mediastinal shift, suspect one of three critical findings: mediastinal fixation by tumor, mainstem bronchus occlusion, or extensive pleural involvement (trapped lung). 1

• This absence of expected mediastinal shift despite large volume is particularly characteristic of mesothelioma due to extensive pleural tumor infiltration 1
• Failure of complete lung expansion after drainage indicates either endobronchial obstruction or trapped lung 5

Pleural Fluid Characteristics

• Bloody pleural fluid with low adenosine deaminase (ADA) activity strongly favors malignancy over infectious causes 2
• Malignant massive effusions show higher median RBC counts (18.0 × 10⁹ cells/L vs 2.7 × 10⁹ cells/L in nonmalignant) and lower ADA activity (11.5 vs 31.5 U/L) 2
• Large/massive malignant effusions demonstrate higher lactate dehydrogenase levels (641 vs 409 U/L) and lower pH (7.39 vs 7.42) compared to smaller malignant effusions 2

Right-Sided Predominance Considerations

• Congestive heart failure causes bilateral effusions, but when unilateral, they are more commonly right-sided 6
• Right-sided effusions meeting exudative criteria in heart failure patients can be identified by elevated pleural fluid NT-proBNP or serum-to-pleural fluid albumin gradient 6
• However, heart failure typically does not cause massive effusions occupying the entire hemithorax 6

Immediate Diagnostic Approach

Initial Evaluation

• Perform diagnostic thoracentesis on any unilateral effusion, sending pleural fluid for nucleated cell count with differential, total protein, LDH, glucose, pH, and cytology 1
• Use thoracic ultrasound to guide all pleural interventions, assess effusion size, and detect septations or loculations 3, 4
• Obtain chest CT to exclude other causes and identify features suggesting complicated parapneumonic or malignant effusion 4

Interpreting Results

• Apply Light's criteria to differentiate exudates from transudates 4
• 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 for definitive diagnosis 1

Critical Pitfalls to Avoid

• Do not assume bilateral effusions exclude malignancy—malignant effusions can be bilateral 1, 7
• Hemoptysis with pleural effusion is highly suggestive of bronchogenic carcinoma 1, 7
• History of asbestos exposure identified on CT (pleural plaques) should raise suspicion for mesothelioma 1
• In parapneumonic effusions, pH less than 7.2 indicates complicated effusion requiring prompt catheter or chest tube drainage 4
• Aminoglycosides should be avoided for pleural infections as they have poor pleural space penetration and are inactive in acidic pleural fluid 3

Management Implications

• Therapeutic thoracentesis should be performed in virtually all dyspneic patients with massive effusions to determine effect on breathlessness and rate of recurrence 5
• Before attempting pleurodesis, complete lung expansion must be demonstrated; initial pleural fluid pressure less than 10 cm H₂O at thoracentesis makes trapped lung likely 5
• All infected pleural effusions require chest tube drainage unless clear contraindications exist, as antibiotics alone are insufficient 3