Interstitial Prominence and Hyperlucency in Lung Imaging
Interstitial prominence refers to thickening of the interstitial structures in the lungs visible on imaging, while hyperlucency indicates abnormally increased radiolucency (darkness) of lung tissue due to decreased density or vascularity.
Interstitial Prominence
Definition and Appearance
- Interstitial prominence represents thickening of the interstitial structures within the lungs, appearing as reticular (net-like) opacities on imaging 1
- Visible on chest X-ray and more clearly defined on high-resolution computed tomography (HRCT)
- Characterized by subpleural reticular abnormalities, often with traction bronchiectasis and bronchiolectasis 1
Common Patterns
- Reticular pattern: Net-like appearance of interstitial thickening
- Subpleural predominance: Often more prominent in peripheral and basal regions 1
- Traction bronchiectasis: Irregular bronchial dilatation caused by surrounding fibrosis 1
- Honeycombing: End-stage fibrosis appearing as clustered cystic spaces with thick walls 1
Clinical Significance
- Indicates inflammation and/or fibrosis of lung parenchyma 2
- Key feature in diagnosing interstitial lung diseases (ILDs)
- When extensive (>5% of lung zone), suggests established interstitial lung disease rather than early interstitial lung abnormalities 1
- Associated with progressive dyspnea and declining lung function 3
Hyperlucency
Definition and Appearance
- Abnormally increased radiolucency (darkness) of lung tissue on imaging 1, 4
- Can be focal, unilateral, or diffuse
- Represents decreased density of lung tissue or reduced vascularity 4, 5
Common Patterns
- Localized hyperlucency: Affecting specific lung segments or lobes
- Diffuse mosaic attenuation: Patchwork of areas with different densities 1
- Lobular air trapping: Hyperlucent lobules visible especially on expiratory CT 1
- Hyperlucent lobules: Seen in conditions like hypersensitivity pneumonitis 1
Clinical Significance
- May indicate:
- When seen with interstitial abnormalities, suggests specific diagnoses like hypersensitivity pneumonitis 1
Diagnostic Approach
Imaging Techniques
- HRCT: Gold standard for evaluating interstitial patterns and hyperlucency 1
- Expiratory CT: Essential to confirm air trapping in hyperlucent regions 1
- Perfusion scanning: Can confirm decreased perfusion in hyperlucent areas 4
Key Diagnostic Features
- For interstitial prominence: Look for reticular abnormalities, traction bronchiectasis, and honeycombing 1
- For hyperlucency: Assess for mosaic attenuation, air trapping on expiratory imaging, and vascular attenuation 1, 4
Clinical Implications
Differential Diagnosis
When both interstitial prominence and hyperlucency are present:
- Hypersensitivity pneumonitis: Shows hyperlucent lobules with interstitial fibrosis 1
- Connective tissue disease-associated ILD: May show mixed patterns 1
- Combined pulmonary fibrosis and emphysema: Areas of fibrosis and hyperlucent emphysema
- Swyer-James-MacLeod syndrome: Unilateral hyperlucency with bronchiectasis 4, 5, 6
Monitoring
- Regular pulmonary function tests (PFTs), especially FVC and DLCO 2, 3
- DLCO is typically the most significantly affected parameter in progressive ILD 2
- A decline of ≥5-10% in FVC indicates clinically significant progression 2, 3
Important Caveats
- Hyperlucency alone may be misinterpreted as normal or even healthy lung tissue
- Interstitial prominence may be subtle on chest X-ray and require HRCT for proper evaluation
- Expiratory imaging is crucial to differentiate between air trapping and true hyperlucency
- Both findings should be interpreted in clinical context, as they can represent various diseases with different prognoses and treatments
- Mosaic attenuation with air trapping is inconsistent with usual interstitial pneumonia pattern, which is important for diagnostic classification 1