| Ground‑glass opacity | ↑ attenuation, vessels visible | active inflammation, oedema, infection (PCP, viral/COVID‑19), haemorrhage, early fibrosis |
| Consolidation | vessels obscured | pneumonia, organising pneumonia, haemorrhage, lepidic tumour |
| Crazy paving | GGO + interlobular septal thickening | PAP, PCP, ARDS, haemorrhage, COVID‑19 |
| Interlobular septal thickening | polygonal lines 1–2 cm | oedema, lymphangitis, sarcoid |
| Honeycombing | clustered subpleural cysts in rows, shared walls | UIP end‑stage fibrosis |
| Traction bronchiectasis | dilated airways within fibrosis | fibrosis (UIP, fibrotic NSIP) |
| Mosaic attenuation | geographic density differences; expiratory air trapping | small airways disease (HP, constrictive bronchiolitis), CTEPH |
| Tree‑in‑bud | centrilobular branching nodules | infective bronchiolitis (TB, NTM, bacterial), aspiration |
| Reversed halo (atoll) | central GGO with peripheral consolidation ring | organising pneumonia, fungal (mucormycosis), TB, COVID‑19 |