Causes of Loculated Pleural Effusion
Loculated pleural effusions develop when excessive fibrin formation from inflammatory processes creates septations that divide the pleural space into multiple separate pockets of fluid, with the primary causes being parapneumonic effusions/empyema, malignancy, and any inflammatory condition that triggers changes in procoagulant and fibrinolytic activity. 1
Primary Etiologic Categories
Infectious/Parapneumonic Causes
- Bacterial pneumonia is the most common infectious cause, with 36-57% of bacterial pneumonias developing parapneumonic effusions that can progress to loculation 2
- The most frequent causative organisms include Streptococcus pneumoniae, Staphylococcus aureus, and β-hemolytic streptococci 3
- Empyema represents the advanced stage where bacterial invasion and fibrin deposition create thick septations and loculations 3
Malignant Causes
- Lung cancer is the most common malignancy causing loculated pleural effusion, followed by breast cancer 4, 5
- Septations are present in approximately 60% of malignant pleural effusions, with 15% showing extensive adhesions that obstruct two-thirds or more of the thoracoscopic view 1
- The extent of pleural adhesions in malignant effusions correlates with greater pleural tumor burden and shorter median survival 1
Inflammatory/Autoimmune Causes
- Lupus erythematosus and rheumatoid disease can cause inflammatory pleural effusions that develop loculations 6
- Tuberculosis is an important cause, particularly in endemic regions 6
Pathophysiologic Mechanism of Loculation Formation
The development follows a predictable three-stage progression 3:
Exudative stage: Clear fluid accumulates with low white cell count, low LDH, physiological pH, and normal glucose 3
Fibropurulent stage: Fibrin deposition occurs in the pleural space, leading to septation and loculation formation, with white cell counts increasing dramatically, LDH rising, protein exceeding 3 g/dL, pleural fluid pH falling below 7.20, and glucose dropping 3
Organizational stage: Fibroblasts infiltrate and convert fibrin strands into thick, non-elastic membranes that prevent lung re-expansion 3
Key Distinguishing Features
Septated vs. Loculated Effusions
- Septated effusions have fibrinous strands within the fluid but allow free flow of fluid within the pleural space 1
- Loculated effusions are divided into multiple separate pockets that prevent complete drainage and limit lung re-expansion, potentially contraindicating pleurodesis 1
Clinical Implications by Etiology
Parapneumonic/Empyema
- Loculated parapneumonic effusions are associated with longer hospital stays and more complicated courses than simple effusions 7
- These require earlier chest tube drainage and often need adjunctive fibrinolytic therapy 7
Malignant Effusions
- Loculation can prevent complete drainage and result in insufficient symptomatic relief even with indwelling pleural catheters 1
- If the underlying lung is non-expandable due to loculations, pleurodesis will be ineffective 7
Common Pitfalls
- Failing to recognize the progression: Septated effusions can become loculated over time if left untreated, but the presence of septations does not necessarily prevent free fluid flow initially 1
- Underestimating inflammatory causes: Any condition causing excessive fibrin formation due to inflammatory-mediated changes in procoagulant and fibrinolytic activity can lead to loculation 1
- Delayed intervention: The fibropurulent stage represents a critical window where intervention can prevent progression to the organizational stage with irreversible fibrosis 3