CT Imaging Examples for COPD and Interstitial Lung Disease
COPD: Characteristic CT Findings
Chest CT without contrast is the imaging modality of choice for visualizing COPD, demonstrating emphysema as low-attenuation areas without visible walls, bronchial wall thickening, and air-trapping on expiratory images. 1
Emphysema Patterns
- Centrilobular emphysema appears as small, focal areas of low attenuation (darker regions) typically in the upper lobes, representing destruction of respiratory bronchioles while sparing the peripheral alveolar ducts 2
- Panlobular emphysema shows more uniform destruction of the entire secondary pulmonary lobule, often predominating in lower lobes 2
- Paraseptal emphysema manifests as subpleural lucencies or cysts, typically along the pleural surfaces and interlobular septa 2
- The severity can be graded visually as trace, mild, moderate, confluent, or advanced destructive emphysema 2
Airway Abnormalities
- Bronchial wall thickening is present in 57-62% of COPD cases and appears as increased soft tissue density surrounding the bronchial lumen 3, 4
- Air trapping on expiratory CT creates a mosaic attenuation pattern—areas of darker (trapped air) and lighter (normal) lung parenchyma—present in 31-35% of cases 3, 4
- Quantitative measurements show low attenuation areas (LAA) with cutoff values typically set at -960 Hounsfield Units; LAA >5.6% suggests COPD even with normal spirometry 5, 6
Technical Imaging Protocol
- Thin-section CT with ≤1.5 mm slice thickness is essential for detecting subtle parenchymal changes 1
- Expiratory phase imaging is mandatory because air trapping and mosaic attenuation are only visible on expiratory cuts 3, 4
- Visual scoring systems (Fleischner classification) combined with quantitative LAA measurements achieve diagnostic accuracy of 0.730-0.943 when combined with clinical characteristics 5
Interstitial Lung Disease: Characteristic CT Findings
HRCT demonstrates ILD through reticular opacities with basal-peripheral predominance, ground-glass attenuation, honeycombing, and traction bronchiectasis—findings that distinguish it from COPD's emphysematous changes. 1, 4
Usual Interstitial Pneumonia (UIP) Pattern
- Honeycombing appears as clustered cystic airspaces (3-10 mm) with thick, well-defined walls arranged in single or multiple layers, predominantly in subpleural and basal regions 4
- Reticular opacities manifest as a network of linear densities representing interlobular septal thickening and intralobular lines, with basal-peripheral distribution 4, 1
- Traction bronchiectasis shows irregular bronchial dilatation caused by surrounding fibrotic tissue pulling on airways—this distinguishes ILD-related bronchiectasis from COPD 1, 4
Ground-Glass Opacities
- Ground-glass opacities (GGO) appear as hazy increased attenuation that does not obscure underlying vessels, representing active inflammation or early fibrosis 4
- Prone imaging is essential to distinguish true GGO from dependent atelectasis, which resolves in the prone position 4
- Extensive GGO with subpleural sparing suggests fibrotic nonspecific interstitial pneumonia rather than UIP 4
Distribution Patterns That Differentiate ILD from COPD
- ILD characteristically shows basal and peripheral predominance, whereas COPD emphysema typically affects upper lobes 1, 4
- Honeycombing in ILD is subpleural, while COPD shows centrilobular or panlobular emphysema without honeycomb cysts 1, 2
- ILD demonstrates architectural distortion with volume loss, contrasting with COPD's hyperinflation 4, 1
Critical Distinguishing Features Between COPD and ILD
Parenchymal Patterns
- COPD: Low-attenuation areas (emphysema) without walls, mosaic attenuation on expiration, preserved lung architecture in non-emphysematous regions 1, 2
- ILD: Increased attenuation (reticular, ground-glass), honeycombing with thick walls, architectural distortion with traction bronchiectasis 1, 4
Bronchiectasis Characteristics
- COPD-associated bronchiectasis occurs in chronic bronchitis phenotype, typically cylindrical, without significant traction 4, 1
- ILD-related traction bronchiectasis shows irregular, distorted airways pulled by surrounding fibrosis, predominantly in fibrotic zones 1, 4
Quantitative Metrics
- COPD: LAA% >5.6% at -960 HU threshold, quantitative airway wall measurements correlate with symptoms 5, 6
- ILD: HRCT achieves 95.7% sensitivity when ≥20% of lung is involved; extent of honeycombing predicts mortality 4
Common Imaging Pitfalls
- Do not confuse dependent atelectasis with ground-glass opacity—always obtain prone images in suspected ILD to clarify subpleural opacities 4
- Bronchiectasis is not specific: 20% of asymptomatic elderly have bronchiectasis on CT; clinical context determines significance 4, 7
- Chest radiography has poor sensitivity: normal chest X-ray does not exclude COPD (misses 34% of bronchiectasis) or early ILD 4
- CT angiography protocols are inadequate for ILD assessment because incomplete inspiration mimics or obscures interstitial disease 4
- Standard chest CT without contrast is sufficient; IV contrast adds no diagnostic value for parenchymal evaluation 1, 4
When to Obtain CT Imaging
COPD Evaluation
- Reserve CT for patients with abnormal chest radiograph requiring characterization, or normal radiograph with persistent symptoms despite empiric treatment 4, 3
- CT detects early COPD in symptomatic smokers with normal spirometry, showing emphysema or air trapping before functional impairment 6, 5
- Quantitative CT phenotypes predict hospitalizations and mortality, but routine surveillance CT is not recommended for stable disease 1, 4
ILD Evaluation
- HRCT is the reference standard for noninvasive ILD diagnosis; obtain when clinical or radiographic findings suggest interstitial disease 4
- In systemic autoimmune disease, perform HRCT only when clinically indicated, not at routine intervals 4
- Multidisciplinary discussion combining HRCT, clinical, and pathologic data improves diagnostic accuracy and may obviate lung biopsy 4