X-ray
CT
Stage 1
- May have a latent period of 24-48 hours with a normal appearance
- Rapid progression of bilateral infiltrates:
- Resemble pulmonary oedema
- Maybe more peripheral than central
- Gravitational gradient usually present
- Coalesce to form diffuse consolidations
- Air bronchograms visible
- Reduced lung volume
- Diffuse bilateral pulmonary infiltrates in non-homogenous distribution:
- Widespread ground-glass attenuation (non-specific sign of reduced air content)
- Often anteroposterior density gradient – suggesting degree of compression atelectasis
- Dense consolidation in dependent regions
- Relatively normal or hyperexpanded lung in non-dependent regions
- Bronchial dilatation within ground-glass areas
- Pulmonary cysts
- Symmetrical changes may be more common in extrapulmonary ARDS
Stage 2
- Usually stable radiological appearance
- Reticular opacities may begin to appear
- Usually stable radiological appearance
- Signs of early fibrosis may be seen which is associated with higher mortality:
- CT opacities >80%
- Bronchiectasis
- Honeycombing
- Pulmonary hypertension
Stage 3
- Variable resolution at unpredictable speed resulting in:
- Normal looking lung
- Coarse reticulations with decreased lung volume
- Variable resolution at an unpredictable rate with 70% showing abnormalities at 6 months:
- Usually persistent ground-glass change, cysts and bullae
- Chronic fibrosis and organisation with honeycombing and traction bronchiectasis