What defines a massive pleural effusion (MPE)?

Definition of Massive Pleural Effusions

Massive pleural effusions are defined as pleural effusions that occupy the entire hemithorax. 1

Radiographic Characteristics

• Massive pleural effusions completely opacify the hemithorax on chest radiography 2
• While only approximately 10% of patients with malignant pleural effusions present with massive effusions, malignancy is the most common cause of massive pleural effusions 1
• Massive effusions can cause contralateral tracheal deviation due to mediastinal shift 3
• The size of pleural effusions correlates with the degree of reduction in breath sounds on physical examination 3

Etiological Considerations

• Malignancy is the predominant cause of massive pleural effusions (55%), followed by complicated parapneumonic effusions/empyema (22%), and tuberculosis (12%) 2
• Lung cancer is the most common malignancy causing pleural effusions, followed by breast cancer 4
• While massive effusions are typically associated with malignancy, hepatic hydrothorax can also present with sizeable effusions 1

Clinical Significance

• Massive pleural effusions are associated with significantly worse survival outcomes in patients with malignant pleural disease 1
• The pathogenesis of dyspnea in massive pleural effusions involves decreased chest wall compliance, contralateral shifting of the mediastinum, decreased ipsilateral lung volume, and reflex stimulation from the lungs and chest wall 1
• Patients with massive effusions typically present with dyspnea, initially on exertion, predominantly dry cough, and pleuritic chest pain 5

Laboratory Characteristics

• Compared to smaller malignant effusions, large/massive malignant pleural effusions show:
  • Higher median red blood cell counts (18.0 × 10⁹ cells/L vs 4.3 × 10⁹ cells/L) 2
  • Higher lactate dehydrogenase levels (641 vs 409 U/L) 2
  • Lower pH (7.39 vs 7.42) 2
  • Similar cytologic yield for malignant cells (63% vs 53%) 2

Diagnostic Approach

• Thoracentesis should be performed for new and unexplained pleural effusions, including massive effusions 5
• Chest CT with contrast is recommended for evaluation of massive effusions, particularly to assess for underlying malignancy 1
• Pleural fluid analysis should include biochemical, microbiological, and cytological studies 5
• Pleural biopsy may be necessary, particularly when malignancy or tuberculosis is suspected 5

Management Considerations

• Management depends primarily on the underlying etiology 6
• Large, symptomatic effusions typically require drainage for symptom relief 5
• For malignant massive effusions, options include:
  • Thoracentesis for immediate symptom relief 4
  • Indwelling pleural catheter placement 4
  • Pleurodesis for prevention of recurrence in appropriate candidates 4
• Early consultation with a thoracic surgeon should be considered for management of massive effusions, particularly when empyema is suspected 7