| Distribution | - Subpleural and basal predominant
- Often heterogeneous (areas of normal lung interspersed with fibrosis)
- Occasionally diffuse
- May be asymmetric
| - Subpleural and basal predominant
- Often heterogeneous (areas of normal lung interspersed with reticulation and traction bronchiectasis/
bronchiolectasis) | - Diffuse distribution without subpleural predominance
| - Peribronchovascular predominant with subpleural sparing (consider NSIP)
- Perilymphatic distribution (consider sarcoidosis)
- Upper or mid lung (consider fibrotic HP, CTD-ILD, and sarcoidosis)
- Subpleural sparing (consider NSIP or smoking-related IP)
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| CT features | - Honeycombing with or without traction bronchiectasis/
bronchiolectasis - Presence of irregular thickening of interlobular septa
- Usually superimposed with a reticular pattern, mild GGO
- May have pulmonary ossification
| - Reticular pattern with traction bronchiectasis/
bronchiolectasis - May have mild GGO
- Absence of subpleural sparing
| - CT features of lung fibrosis that do not suggest any specific etiology
| - Lung findings
- Cysts (consider LAM, PLCH, LIP, and DIP)
- Mosaic attenuation or three-density sign (consider HP)
- Predominant GGO (consider HP, smoking-related disease, drug toxicity, and acute exacerbation of fibrosis)
- Profuse centrilobular micronodules (consider HP or smoking-related disease)
- Nodules (consider sarcoidosis)
- Consolidation (consider organizing pneumonia)
- Mediastinal findings
- Pleural plaques (consider asbestosis)
- Dilated esophagus (consider CTD)
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