What Are Pleural Parenchymal Opacities?
Pleural parenchymal opacities are radiographic findings on chest imaging that represent abnormalities involving both the pleural surface (the lining around the lungs) and the adjacent lung tissue (parenchyma), appearing as areas of increased density or whiteness on X-rays or CT scans. 1
Anatomic Definition
Pleural parenchymal opacities specifically describe:
- Irregular pleural-based opacities with associated reticular patterns and parenchymal distortion 1
- Scattered pleuroparenchymal opacities affecting the underlying lung parenchyma 1
- Abnormalities that can involve subpleural regions where the pleura meets the lung tissue 1
Common Causes and Clinical Contexts
Asbestos-Related Disease
- Diffuse pleural thickening with parenchymal bands suggests diffuse fibrosis involving the visceral pleura 1
- Subpleural fibrosis associated with pleural thickening is characteristic of asbestos exposure 1
- These findings typically appear as bilateral irregular opacities in the lower lobes 1
Pleuroparenchymal Fibroelastosis (PPFE)
- Dense subpleural consolidation with traction bronchiectasis and architectural distortion 2
- Predominantly affects upper lobes with characteristic pleural-based opacities 2
- Associated with pneumothorax risk and recurrent infections 2
Organizing Pneumonia
- Patchy consolidation in subpleural, peribronchial, or bandlike patterns 1
- Can present with migratory opacities that change location over time 1
- May be associated with small pleural effusions in 10-30% of cases 1
Pulmonary Embolism
- Wedge-shaped peripheral opacities are significantly associated with PE (odds ratio 6.78) 3
- These represent areas of pulmonary infarction adjacent to the pleural surface 4, 3
Imaging Characteristics
On Chest X-ray
- Appear as bilateral small irregular opacities, often in lower lobes 1
- Limited sensitivity—15-20% of histologically confirmed cases may have normal chest radiographs 1
- Overlying pleural disease may obscure parenchymal markings 1, 5
On High-Resolution CT (HRCT)
- HRCT is far superior to chest X-ray for detecting these abnormalities 1
- Shows subpleural "dotlike" opacities, subpleural lines, and parenchymal bands 1
- Can detect pleural thickening as thin as 1-2 mm 1
- Prone views are essential to distinguish dependent atelectasis from true parenchymal fibrosis 1
Clinical Significance
When to Investigate Further
- Persistent opacities warrant CT evaluation to differentiate between infectious, inflammatory, and fibrotic causes 5
- The American College of Radiology recommends further investigation as these may represent various pathologies including parapneumonic effusion, empyema, or interstitial lung disease 5
Diagnostic Approach
- HRCT should be obtained at 2-cm intervals for accurate assessment 1, 5
- Consider diagnostic thoracentesis if pleural effusion is present 5
- Evaluate for occupational exposures (particularly asbestos) 1
- Assess for connective tissue diseases and other systemic conditions 6
Important Caveats
Non-Specific Finding
- Parenchymal opacification on CT is nonspecific and can affect air spaces, interstitium, or both 7
- In 86% of cases, these findings indicate potentially treatable or reversible disease 7
- The majority of patients with and without PE demonstrate parenchymal and pleural findings, making differentiation challenging 8, 3