Diffuse Pleural Thickening

Jeffrey P. Kanne, MD

DIFFERENTIAL DIAGNOSIS

Common

Less Common

Rare but Important

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Definition of diffuse pleural thickening not standardized
Commonly used definitions
- Radiography
  - Extends more than 25% of chest wall
  - > 5 mm thickness at least at 1 site
  - Often involves costophrenic sulcus
- CT
  - > 5 cm wide
  - > 8 cm craniocaudad extent
  - > 3 mm thick
Less rigorous criteria may be appropriate
- Lesser degree of pleural thickening may be functionally significant
Extrapleural fat can mimic diffuse pleural thickening (fat attenuation)
- Typically bilateral, symmetric, sparing costophrenic sulcus
Often associated with parenchymal bands and rounded atelectasis

Helpful Clues for Common Diagnoses

Exudative Pleural Effusion
- Usually unilateral
- Pleural thickening is late finding
  - Persists despite resolution of pleural effusion
- Adjacent pneumonia or other pulmonary inflammation may present initially
  - Streptococcal and staphylococcal species most common
  - Nosocomial infection with gram-negative anaerobes and methicillin-resistant Staphylococcus aureus (MRSA)
- Can calcify over time, though uncommon
Empyema
- Tuberculosis and streptococcal pneumonia most common causes
- Usually unilateral
- Pleural thickening is late finding
- Adjacent pneumonia or other pulmonary inflammation may initially be present
- Extensive calcification most commonly from tuberculosis
Asbestos-related Pleural Disease
- 10% of asbestos-exposed individuals affected
- Distinct from pleural plaques
- Affects primarily visceral pleura
- Bilateral involvement more common than unilateral involvement
- Often associated with significant restrictive respiratory impairment
- Often associated with parenchymal bands and rounded atelectasis
Hemothorax
- Usually unilateral
- Blunt or penetrating trauma
- Iatrogenic
- Parietal or visceral pleural thickening
  - Can develop rather quickly
  - Varying amount of residual pleural fluid
  - May calcify over time
- Adjacent rib fractures suggestive
Thoracotomy
- Mild residual pleural thickening common
- Usually smooth, mild thickening
- Can result from postoperative hemothorax

Helpful Clues for Less Common Diagnoses

Pleural Metastasis
- ˜ 90% of all pleural neoplasms
  - Lung carcinoma leading cause
  - Breast, ovary, and gastric carcinomas and lymphoma also common causes
- Usually multiple
- Can simulate benign pleural disease
- Nodular, circumferential, and mediastinal pleural involvement suggestive of malignancy
- Associated pleural effusion common
- Can have lung or thoracic lymph node metastases
Radiation-induced Lung Disease
- Usually complication of radiation therapy for breast cancer, lung cancer, or lymphoma
- Small residual pleural effusion may be present
- Radiation-induced lung fibrosis often present in radiation field
Systemic Lupus Erythematosus
- Pleural thickening most common intrathoracic manifestation
  - Occurs in up to 30% in autopsy series
- Unilateral more common than bilateral
- Pleural effusion frequently present
Rheumatoid Arthritis
- Pleural diseases are most common intrathoracic manifestation
- 40-70% pleural involvement in autopsy series
- Pleural effusion may accompany pleural thickening
- Unilateral more common than bilateral
Pleurodesis
- Variable degrees of pleural thickening and nodularity
  - Remain stable over time
  - May enhance with large amount of granulation tissue
- Residual loculations of fluid common
- High-attenuation deposits (from talc) mimic pleural calcification
  - Usually adjacent to dependent lung
  - May be lentiform

Helpful Clues for Rare Diagnoses