Chest radiographs and computed tomography are the imaging techniques of choice.
The first one is primarily used to support the diagnosis,
to spot the complication and for continuous monitoring; the latter is preferred for a better characterisation of the disease,
its extension and its complications.
Chest radiographs
Chest radiograph findings of ARDS vary widely depending on the stage of the disease.
Diffuse alveolar opacities pointing out consolidation are counted as the first imagistic result Fig. 1 .
Air bronchogram is visible.
The opacities progress into a more asymmetrical and extended shape.
One cannot usually find septal lines thickening or pleural effusion.
These are more specific to a congestive heart failure Fig. 2 Fig. 3 .
This is the exudative stage.
Serial chest radiographs may help distinguish between ARDS and other pathologies because a severe change in the imagistic aspect after 5-7 days may indicate another diagnosis Fig. 4 .
If the patient survives,
the disease enters in the fibrotic stage.
The aspects of the chest radiography may reveal interstitial syndrome,
which is not necessarily due to fibrosis.
A correlation between pathological specimens and conventional radiographs was not possible.
The latter tend to stabilise in 10-14 days,
but a complete recovery can last up to a couple of months,
depending on the cause and the patient’s response to treatment.
Computed tomography
CT scans depicts a 3-layered pattern due to the gravitational gradient.
On the ventral side one can find normal lung images.
As the pressure sums up towards the dorsal side ground glass opacities appear and they multiply in number Fig. 6 .
On the most posterior aspect full consolidations emerge,
pointing to the greatest gravitational gradient Fig. 7 .
Also a caudal augmentation of the lesions can be seen.
A review of chest CT scans in 74 patients with ARDS revealed the following findings:
- Areas of consolidation with air bronchograms (89%) Fig. 9
- Bilateral abnormalities in almost all the patients,
predominantly dependent abnormalities (86%)
- Basilar predominant abnormalities (68%)
- Patchy abnormalities (42%) Fig. 5
- Mixed ground-glass appearance and consolidation (27%)
- Homogeneous abnormalities (23%)
- Ground-glass attenuation (8%)
The same study revealed that in two thirds of the cases the CT scans brought significant additional information.
ARDS that is due to pulmonary disease tends to be asymmetrical,
with a mix of consolidation and ground-glass opacification,
whereas ARDS that is due to extrapulmonary causes has predominantly symmetric ground-glass opacification Fig. 8 . Air bronchograms and pleural effusions have a bigger prevalence than pneumatoceles and Kerley B lines.
CT scans are a valuable asset in revealing ARDS complications such as pleural abnormalities (pneumothorax),
parenchymal disease (nodules,
focal opacities,
interstitial emphysema) and mediastinal disease (enlarged lymph nodes).
By comparison with the chest radiographs,
the CT scans have a role in the detection of suspected fibrosis as the changes that accompany fibrosis become more apparent,
such as: traction bronchiectasis,
lobular distortion,
and in advanced cases,
cystic lung destruction or honeycombing.
The implications of imaging in understanding ARDS has changed in the last years.
It is now known that there is a marked reduction in overall lung volume at the expense of the volume of the lower lobes.
Two mechanisms contribute to this: in the upper lobes there is an increase in tissue (edema,
inflammation),
in the lower lobes there is a loss of aeration (abdominal content,
compression by heart).
These facts helped the optimisation of PEEP treatment.
CT proves to be important in improving the treatment,
by examining the evolution of the disease after a drug treatment or a procedure and especially in long term check-ups.