Acute GGO — Diffuse
- Pulmonary edema (cardiogenic)
- ARDS / DAD
- PCP (Pneumocystis jiroveci)
- Viral pneumonia (influenza, RSV, COVID-19)
- Pulmonary hemorrhage (diffuse alveolar hemorrhage)
- Aspiration (bilateral)
- Drug toxicity (acute)
Acute GGO — Focal / Multifocal
- Bacterial pneumonia (early lobar or bronchopneumonia)
- Pulmonary infarct (PE)
- Aspiration (segmental)
- Pulmonary contusion / hemorrhage
- Radiation pneumonitis (early)
- Focal organizing pneumonia
Chronic GGO — Diffuse
- NSIP (GGO + reticulation + subpleural sparing)
- DIP (lower lobe GGO in smoker)
- LIP (GGO + perivascular cysts; Sjögren)
- Subacute/Chronic HP
- PAP (crazy paving, perihilar geographic distribution)
- Drug toxicity (chronic)
- Chronic pulmonary edema
Chronic GGO — Focal / Multifocal
- AIS / MIA / lepidic adenocarcinoma (persistent pure GGO nodule)
- Invasive adenocarcinoma
- COP (peribronchovascular, migrating)
- Focal HP
- Sarcoidosis (GGO variant)
- Mucinous adenocarcinoma
Pattern-Based Narrowing
| Pattern | Top Diagnoses | Distinguishing Clue |
|---|---|---|
| Crazy paving (GGO + smooth septal thickening) | PAP, PCP, ARDS, pulmonary edema, COVID-19, lipoid pneumonia | PAP: perihilar, geographic lucent rims. PCP: upper lobe, HIV/immunosuppression. Edema: Kerley B lines, effusions. |
| GGO + consolidation | COP, AIP/DAD, bacterial PNA, hemorrhage, mucinous adenocarcinoma | COP: migrating, peribronchovascular, reverse halo. AIP: rapid progression. Hemorrhage: hemoptysis. |
| GGO + reticulation (no honeycombing) | NSIP, fibrotic HP, drug toxicity, edema | NSIP: subpleural sparing, CTD association. HP: upper-lobe bias, mosaic air trapping. |
| GGO + cysts | LIP, DIP, LAM, LCH, PCP (pneumatoceles) | LIP: perivascular cysts + Sjögren. DIP: lower lobe, smoker. LAM: uniform bilateral cysts, young woman. |
| Pure GGO nodule(s) | AIS / MIA / lepidic adenocarcinoma, focal HP, AAH | Persistent >3 months → adenocarcinoma spectrum. Fleischner: follow at 6–12 mo if ≥6 mm. Solid component growth = upgrade concern. |
| Diffuse GGO, no other features | DIP, NSIP (cellular), drug reaction, viral PNA, PCP, alveolar hemorrhage | Acuity is key: acute = infection/edema/hemorrhage; chronic = DIP/NSIP. Smoker + lower lobe = DIP. |
| Mosaic attenuation (GGO + lucent areas) | HP, small airways disease, chronic PE, vasculitis | Air trapping on expiratory CT: lucent areas stay lucent = small airways disease or HP. Normal expiratory enhancement = vascular cause. |
Technical note: Evaluate GGO only on thin-section HRCT (≤1.25 mm). Thick-section or motion-degraded images create pseudoground-glass from averaging effects. Confirm in 2 planes.
References
Raju S et al. Ground-glass opacity of the lung: A systematic approach. Indian J Radiol Imaging. 2017;27(2):176–184.