Split pleura sign = empyema: Enhancement and thickening of both visceral and parietal pleural layers with fluid separating them. Loculated effusion + fever + elevated WBC = empyema until proven otherwise — requires drainage. Distinguish from lung abscess: empyema is lenticular, conforms to pleural space, acute angles with chest wall; abscess is within parenchyma, surrounded by lung.
Pleural Disease — Imaging Characteristics
| Diagnosis | Imaging Findings | Key Points |
|---|---|---|
| Simple effusion (transudate) | Dependent layering; meniscus sign on upright CXR; blunting of costophrenic angle (>200 mL); CT HU 0–15; no pleural enhancement | Causes: CHF, cirrhosis, nephrotic syndrome; bilateral in CHF; treat underlying cause |
| Empyema | Lenticular collection conforming to pleural space; split pleura sign; loculations; CT HU 10–40; obtuse angles with chest wall | Complication of pneumonia, trauma, surgery; requires drainage; thickened pleura + loculations = complex empyema |
| Hemothorax | CT HU 35–70 (acute blood); dependent layering; hematocrit effect | Trauma, coagulopathy, malignancy; loculation develops rapidly; retained hemothorax → fibrothorax; drain if large or infected |
| Chylothorax | CT HU near water (0–20); bilateral; large volume; may have fat-fluid level | Thoracic duct injury, lymphoma, post-surgical; triglycerides >110 mg/dL diagnostic |
| Malignant effusion | Nodular pleural thickening; >1 cm thickness; circumferential enhancement; mediastinal pleural involvement | Lung, breast, lymphoma, mesothelioma most common |
Mesothelioma
Malignant pleural mesothelioma is a primary pleural malignancy almost universally associated with asbestos exposure. CT hallmarks:
- Unilateral circumferential pleural thickening (often "rind-like")
- Mediastinal pleural involvement — distinguishes from benign asbestos-related pleural disease
- Volume loss of the affected hemithorax (encasement) — no mediastinal shift despite large effusion
- Nodular or lobulated pleural masses
- Invasion of chest wall, diaphragm, or mediastinum in advanced disease
Absence of mediastinal shift despite large unilateral effusion should raise concern for mesothelioma — encasement prevents lung from collapsing.
Asbestos-Related Pleural Disease
| Finding | Features | Significance |
|---|---|---|
| Pleural plaques | Calcified or non-calcified; bilateral; parietal pleura; diaphragmatic surface; spare costophrenic angles and apices | Marker of asbestos exposure; not premalignant |
| Diffuse pleural thickening | >5 mm; extends over >25% of chest wall; bilateral | Can cause restrictive lung function |
| Rounded atelectasis | Curvilinear opacity with "comet tail" sign (vessels/bronchi curving into the opacity); associated pleural thickening | Benign; may mimic mass — comet tail sign is diagnostic |