Acute Respiratory Distress Syndrome (ARDS) is a diffuse inflammatory lung injury leading to increased alveolar-capillary permeability, non-cardiogenic pulmonary edema, and severe hypoxemia. Imaging plays a key role in diagnosis, staging, and monitoring.
🩻 Chest X-Ray (CXR) Findings
1. Early Stage (Exudative Phase – 0–7 days)
- Bilateral patchy alveolar opacities — usually symmetrical.
- Diffuse “ground-glass” or airspace pattern, often starting in lower zones.
- No cardiomegaly or pleural effusion → helps differentiate from cardiogenic edema.
- Air bronchograms common.
- Rapid progression over 24–48 hours.
2. Intermediate Stage (Proliferative Phase – 7–21 days)
- Coalescing opacities forming diffuse consolidation.
- Volume loss due to atelectasis.
- Persistent bilateral involvement despite supportive therapy.
3. Late Stage (Fibrotic Phase – >3 weeks)
- Reticular or linear opacities due to interstitial fibrosis.
- Traction bronchiectasis or honeycombing pattern.
- Lung volume reduction, especially in lower lobes.
💻 CT Findings (More Sensitive & Specific)
Early/Exudative Phase:
- Ground-glass opacities (GGO) with interlobular septal thickening.
- Dependent consolidation (posterior & basal) with anterior GGO → “dorsal gradient” pattern.
- Air bronchograms often visible.
Proliferative Phase:
- Patchy consolidation
- Crazy-paving pattern (GGO + interlobular septal thickening).
- Subpleural sparing may be noted.
Fibrotic Phase:
- Diffuse reticulation, cystic changes, honeycombing.
- Architectural distortion and volume loss.
⚕️ Key Differentiating Points
| Feature | ARDS | Cardiogenic Pulmonary Edema |
|---|---|---|
| Heart size | Normal | Enlarged |
| Pleural effusion | Uncommon | Common |
| Opacities | Bilateral, patchy, peripheral | Central, perihilar |
| Response to diuretics | Poor | Rapid improvement |
🧠 Teaching Pearls
- Always correlate with clinical context & PaO₂/FiO₂ ratio (<300 mm Hg = ARDS).
- CXR changes lag behind clinical severity.
- CT helps guide ventilation strategy (prone positioning, PEEP optimization).
- Chronic ARDS → risk of fibrosis and barotrauma (pneumatoceles, pneumothorax).
