What are the causes of pleural thickening on a computed tomography (CT) chest scan?

Causes of Pleural Thickening on CT Chest

Pleural thickening on CT chest has three major categories of causes: malignant disease (mesothelioma and metastatic disease), infectious/inflammatory conditions (parapneumonic effusion, empyema, tuberculosis), and asbestos-related benign disease (pleural plaques and diffuse pleural thickening).

Malignant Causes

Malignant pleural mesothelioma and metastatic pleural disease are critical diagnoses to exclude when pleural thickening is identified.

Key CT Features Suggesting Malignancy

• Circumferential pleural thickening >1 cm with nodularity involving the mediastinal surface strongly suggests malignancy 1
• Pleural nodularity has 86-97% specificity for malignancy (though sensitivity is only 37-48%) 2
• Chest wall invasion is characteristic of malignant disease 1
• Mediastinal pleural involvement has 70-74% sensitivity and 83-93% specificity for malignancy 2
• Mass involving extrapleural fat suggests co-existent malignancy 1

Distinguishing Mesothelioma from Metastatic Disease

• Lung parenchymal nodules or masses within lung tissue favor metastatic disease over mesothelioma 2
• Mediastinal or hilar lymph node enlargement is more suggestive of metastatic pleural disease 2
• Presence of pleural plaques suggests asbestos exposure history, supporting mesothelioma 2

Infectious Causes

Parapneumonic Effusion and Empyema

CT features more common in pleural infection than malignancy include: 1

• Lentiform (lens-shaped) configuration of pleural fluid
• Visceral pleural thickening ("split pleura sign")
• Hypertrophy of extrapleural fat (>2 mm)
• Increased density of extrapleural fat
• Presence of pulmonary consolidation

Important caveat: These features have poor sensitivity (0.20-0.48), so diagnostic thoracentesis remains essential for unexplained effusions 1

Tuberculous Pleuritis

• TB pleuritis can mimic malignancy with circumferential pleural thickening >1 cm, mediastinal surface involvement, and nodularity 1
• Unlike malignancy, TB is NOT associated with chest wall invasion 1
• On ultrasound, tuberculous effusions show highly complex internal septations, unlike malignancy 1

Non-Infectious Inflammatory Causes

Non-infective inflammatory conditions typically show mild smooth thickening of the parietal pleura NOT involving the mediastinum 1

Specific Conditions Include:

• Rheumatoid arthritis 1
• Dressler syndrome (post-myocardial infarction) 1
• Organizing pneumonia 1
• Pulmonary emboli 1
• Benign asbestos-related pleural effusion 1

Chronic inflammatory effusions commonly develop pleuroparenchymal bands and subsequently folded lung 1

Asbestos-Related Benign Pleural Disease

Pleural Plaques (Parietal Pleural Fibrosis)

• Bilateral in two-thirds of cases, but can be unilateral 3
• Typically <1 cm thick with regular or polycyclic margins 4
• Calcifications present in 80% of cases 4
• Most commonly involve pulmonary pleura in mid-chest, diaphragmatic pleura (50%), and lower regions (80%) 4
• Pleural plaques are specific markers of asbestos exposure 1, 4

Diffuse Pleural Thickening (Visceral Pleural Fibrosis)

• Defined as pleural thickening ≥3 mm thickness measuring >5 cm axially and >8 cm craniocaudally 1
• Unilateral in 62% of cases 3
• Associated with pleuroparenchymal bands ("crow's feet") and folded lung 1, 3
• Mean latency period of 30-38 years from asbestos exposure 1
• May obliterate costophrenic angle 1

Benign Asbestos Pleural Effusion (BAPE)

• Occurs most frequently on the right (69-76%) but may be bilateral 1
• Can be indistinguishable from early-stage mesothelioma on CT, making it a diagnosis of exclusion 1
• Calcified pleural plaques may be present as concomitant findings 1
• Requires follow-up imaging for up to 24 months to exclude occult malignancy 1

Post-Traumatic and Post-Surgical Causes

Trauma-Related

• Rib fractures visible on CT 1
• Signs of active bleeding 1
• High density on CT in acute phase 1

Post-Cardiac Surgery

• Temporal relationship with surgery 1
• Usually left-sided 1

Cardiac and Abdominal Causes

Cardiac Dysfunction

• Usually bilateral pleural thickening/effusion 1
• Associated cardiomegaly and pericardial effusion 1

Abdominopelvic Pathology

• Signs of cirrhosis on CT 1
• Adnexal mass may be visible 1

Critical Diagnostic Pitfalls

Common pitfalls to avoid:

• Normal structures and extrapleural fat can mimic pleural plaques 5
• Interlobar pleural thickening may mimic lung nodules on CT 1
• Approximately 5% of cases have co-existent malignancy and pleural infection 1
• CT features alone cannot definitively distinguish benign from malignant disease—tissue diagnosis is often required 2

Recommended Diagnostic Approach

1. Assess for high-risk malignant features first: circumferential thickening >1 cm, nodularity, mediastinal involvement, chest wall invasion 1, 2
2. Look for infectious features: lentiform fluid, split pleura sign, extrapleural fat changes, consolidation 1
3. Evaluate for asbestos exposure history and associated findings: pleural plaques, parenchymal bands, folded lung 1
4. Consider clinical context: trauma history, recent surgery, cardiac disease, systemic inflammatory conditions 1
5. Perform diagnostic thoracentesis for unexplained effusions given poor sensitivity of imaging features alone 1
6. Obtain tissue biopsy when malignancy cannot be excluded by imaging and fluid analysis 2