Adult Respiratory Distress Syndrome
Adult respiratory distress syndrome (ARDS) occurs as a response to a variety of insults
including trauma, sepsis, pancreatitis, and drug overdose. Leakage of protein-rich fluid from
damaged capillary membranes into the interstitial and alveolar spaces leads to decreased
inflated lung volumes and decreased lung compliance (37).
On chest radiographs, there are diffuse bilateral opacities located more peripherally due
to predominance of capillaries in the periphery of the lung. Presumably, proteinaceous fluid
remains in the periphery rather than migrating centrally due to poor diffusion, and there is
decreased clearance of the material leading to persistence of the opacities for days to weeks
with little change in appearance. CT findings include bilateral ground-glass opacities,
consolidation, or a combination of both. Opacities are most often most severe in dependent
portions of the lung (44,46).
Interstitial Lung Disease
Interstitial lung diseases (ILDs) are, in general, chronic inflammatory processes that may result
in fibrotic change. There are many classifications of the disease, describing both etiology and
pattern of pulmonary change. Usual interstitial pneumonia (UIP), the most common of the
ILDs, is initially seen on chest radiographs as bibasilar fine reticular opacities progressing to a
coarse reticular or reticulonodular pattern and eventual honeycombing and loss of lung
volume. On CT, areas of ground-glass opacity are seen with irregular septal and subpleural
thickening and eventual honeycombing and traction bronchiectasis. Pulmonary fibrosis, while
not always seen in ILD, is a helpful feature in differentiating it from pneumonia (Fig. 28). The
time course is also more likely to be chronic, based on months to years, rather than acute or
subacute as with pneumonia (37).
Bilateral Massive Aspiration
Aspirated material may include food, water, or sand (as in near drowning) or other foreign
objects such as dental material. On chest radiographs, the characteristic appearance is of
dependent pulmonary opacities, which then typically coalesce. In healthy individuals, the
opacities should resolve rapidly because of mucociliary clearance. There are other specific
findings on both radiographs and CT depending on the material aspirated. A specific foreign
body may be identified within a bronchus. Legumes, such as lentils, are known to cause a
granulomatous pneumonitis. Also, sand or gravel particles may become lodged in small
airways, leading to the diagnostic appearance of sand or gravel bronchograms (37,47).
CONCLUSION
In conclusion, imaging is extremely helpful and often necessary in the diagnosis of infection in
a critically ill patient. However, neoplastic and autoimmune processes can have very similar
appearances on imaging. Subtle findings are often relied upon to separate these entities and in
Figure 28 CT scan of the chest in a female
with rheumatoid arthritis demonstrates periph-
eral fibrotic changes (arrows) compatible with
rheumatoid arthritis (RA)-associated interstitial
lung disease.Radiology of Infectious Diseases and Their Mimics in Critical Care 99