Introduction
Interstitial lung disease (ILD) is a broad group of disorders characterized by inflammation and fibrosis of the lung interstitium.
High-resolution CT (HRCT) is the gold standard imaging modality, as chest radiographs are often nonspecific. Recognizing ILD patterns on HRCT is crucial for diagnosis, narrowing differentials, and guiding biopsy or treatment decisions.
Chest X-Ray Features (Initial Clues)
- Reticular or reticulonodular opacities.
- Volume loss (often bilateral and diffuse).
- Ground-glass haziness in advanced disease.
- Often nonspecific → HRCT is essential.
HRCT Patterns in ILD
📊 HRCT Patterns in Interstitial Lung Disease – Comparison Table
| Pattern | Distribution | Key HRCT Findings | Typical Associations |
|---|---|---|---|
| Usual Interstitial Pneumonia (UIP) | Basal + subpleural predominant | Honeycombing, reticular opacities, traction bronchiectasis | Idiopathic Pulmonary Fibrosis (IPF), Rheumatoid arthritis |
| Nonspecific Interstitial Pneumonia (NSIP) | Lower lobe, symmetric | Ground-glass opacities, fine reticulation, minimal/no honeycombing | Connective tissue disease (Scleroderma, Myositis), Drug-induced ILD |
| Organizing Pneumonia (OP/COP) | Peribronchovascular or peripheral | Patchy consolidation, “Reverse halo (Atoll) sign” | Cryptogenic OP, Post-infectious, Drug reactions |
| Hypersensitivity Pneumonitis (HP) | Mid- and upper-lung predominant | Centrilobular nodules, mosaic attenuation, air trapping | Bird fancier’s lung, Farmer’s lung, Mold exposure |
| Sarcoidosis | Upper lobe + perilymphatic | Nodules along bronchovascular bundles, septa, subpleural regions; Fibrosis in advanced disease | Sarcoidosis (systemic granulomatous disease) |
1. Usual Interstitial Pneumonia (UIP)
- Basal and subpleural predominant fibrosis.
- Honeycombing: clustered cystic airspaces.
- Reticular opacities with traction bronchiectasis.
- Classic in Idiopathic Pulmonary Fibrosis (IPF).
2. Nonspecific Interstitial Pneumonia (NSIP)
- Symmetric, lower lobe ground-glass opacities.
- Fine reticulations, minimal honeycombing.
- Seen in connective tissue disease-related ILD.
3. Organizing Pneumonia (OP / COP)
- Patchy, peribronchovascular or peripheral consolidation.
- “Reverse halo sign” (atoll sign).
- Often migratory lesions.
4. Hypersensitivity Pneumonitis (HP)
- Centrilobular ground-glass nodules.
- Mosaic attenuation with air-trapping.
- Mid- and upper-lung predominance.
5. Sarcoidosis
- Perilymphatic nodules (along bronchovascular bundles, septa, subpleural regions).
- Upper lobe predominant fibrosis.
- Hilar and mediastinal lymphadenopathy.
Role of Radiology in ILD
- Early detection of fibrotic changes before X-ray shows findings.
- Pattern recognition on HRCT helps narrow diagnosis.
- Guide biopsy site selection in atypical cases.
- Monitoring disease progression and response to therapy.
Teaching Points
- ILD = chronic interstitial process → ground glass, reticulation, honeycombing.
- HRCT is the investigation of choice.
- Always classify into UIP, NSIP, OP, HP, or sarcoidosis pattern.
- Radiology + clinical context + serology = best diagnostic approach.
Conclusion
Radiology, especially HRCT, plays a central role in diagnosing and classifying ILD. By recognizing hallmark imaging patterns such as honeycombing in UIP, ground-glass in NSIP, or perilymphatic nodules in sarcoidosis, radiologists can significantly narrow the differential diagnosis and guide patient management.
