What are pleural peels?

Pleural Peels: Definition and Clinical Significance

Pleural peels are thick fibrous membranes that form on the pleural surfaces during the organizational stage of pleural infection, restricting lung expansion and potentially causing trapped lung syndrome. 1

Pathophysiology and Development

Pleural peels develop as part of the natural progression of pleural infection, which occurs in three distinct stages:

1. Exudative stage: Initial inflammatory process with accumulation of clear fluid in the pleural space (simple parapneumonic effusion)

2. Fibropurulent stage: Fibrin deposition leading to septations and loculations, with increasing white cell count and thickening fluid (complicated parapneumonic effusion progressing to empyema)

3. Organizational stage: Fibroblasts infiltrate the pleural cavity, reorganizing thin intrapleural membranes into thick, non-elastic "peels" 1

During the organizational stage, these fibrous peels form on both the visceral and parietal pleural surfaces. They are composed of organized fibrin and collagen deposited by fibroblasts as part of the inflammatory healing response.

Clinical Consequences

The formation of pleural peels can lead to several significant clinical problems:

• Trapped lung: Prevention of normal lung re-expansion due to the restrictive, non-elastic nature of the peel 1, 2
• Impaired lung function: Restrictive ventilatory defect
• Persistent pleural space: Creates ongoing potential for infection
• Chronic sepsis: If not properly managed 1

The trapped lung phenomenon occurs specifically when a fibrous visceral pleural peel prevents the lung from expanding to fill the thoracic cavity, resulting in a chronic, fluid-filled pleural space maintained by hydrostatic equilibrium. 2

Diagnosis

Pleural peels can be identified through various imaging modalities:

• CT scan with contrast: Most useful for visualizing pleural thickening and determining the extent of the peel. Contrast enhancement helps differentiate the peel from adjacent structures 1
• Ultrasound: Can demonstrate pleural thickening and loculations
• Chest radiography: May show persistent pleural opacity and volume loss

Importantly, contrast-enhanced CT scanning cannot accurately differentiate between early and late fibrinopurulent stage disease, and pleural thickness on CT does not reliably predict outcomes from tube drainage. 1

Management

Management of pleural peels depends on symptoms and clinical impact:

1. Observation: For asymptomatic patients with stable radiographic findings, observation is appropriate as pleural peels may resolve over several weeks without intervention 1, 2

2. Surgical intervention: For symptomatic patients with:

   • Restricted lung expansion
   • Chronic sepsis with fever
   • Significant respiratory compromise

3. Surgical options:

   • Decortication: Formal thoracotomy with excision of both visceral and parietal pleural rinds to achieve proper lung re-expansion 1
   • This procedure requires sharp dissection and may result in significant bleeding, air leaks, or nerve damage

Important Clinical Considerations

• Early recognition of developing organization is essential to avoid significant morbidity 1
• CT scanning with intravenous contrast is valuable before surgery to define peel thickness and check for intralobar pathology 1
• Pleural peels may resolve spontaneously over several weeks in some patients 1
• Residual calcification, extrapleural tissue thickening, and pleural scarring may persist long after treatment 1

Differential Diagnosis

Pleural peels must be differentiated from:

• Mesothelioma (which is progressive and typically more symptomatic)
• Diffuse pleural thickening from other causes (tuberculosis, trauma, prior surgery)
• Rounded atelectasis (folded lung appearing as a mass)
• Pachypleuritis (extensive pleural fibrosis with active inflammation) 1

Early intervention with appropriate drainage and fibrinolytic therapy during the fibropurulent stage may help prevent progression to the organizational stage and subsequent peel formation, highlighting the importance of prompt and effective management of pleural infections.