Practice Questions
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Question 1:
a) What are adjectives used to describe airspace disease (alveolar disease) on chest radiography.
Alveolar disease is typically described as fluffy, ill-defined or cloudy. The margins of abnormalities are indistinct.
b) What is the most specific finding on chest radiography indicating an alveolar process?
The air bronchogram is the most specific chest radiographic finding indicating an airspace or alveolar process, but air bronchograms may be subtle on radiography, and are much better seen on CT.
c) What are adjectives used to describe interstitial disease on chest radiography?
Interstitial disease is typically described as linear or reticular (well-defined), and may show Kerley B lines (although these are also better seen on CT than radiography).
d) What is the most specific finding on chest radiography indicating an interstitial process?
Kerley B lines are the most specific finding indicating an interstitial process, but they are often very subtle. Kerley B lines are best seen in the lower lungs near the costophrenic angles.
Question 2:
a) What is the significance of lobar distribution of an airspace/alveolar process?
For airspace processes, many of which represent pneumonia, lobar distribution suggests the common community-acquired pneumonia, like strep pneumoniae (pneumococcus).
b) What is the significance of a diffuse distribution of an airspace/alveolar process?
A more diffuse distribution of airspace disease suggests an atypical pneumonia, like viral, or mycoplasma.
c) What is the significance of adenopathy in the setting of a likely lobar pneumonia?
Most pneumonias are not associated with adenopathy in the chest, so presence of enlarged nodes should make tuberculosis a much more likely diagnosis.
d) What is the significance of a peripheral distribution of fibrotic lung disease?
Both asbestosis and UIP/IPF can have a peripheral distribution, so recognition of this can aid in differential diagnosis.
e) What is the significance of a basilar distribution of interstitial lung disease?
Many diseases have a basilar distribution, but a sharply demarcated basilar region of fibrosis may suggest scleroderma. Pulmonary edema is usually worst in the bases in ambulatory patients, but may be more posterior in patients who are supine, since fluid accumulates in a gravity-dependent manner.
Question 3:
a) What is the appearance and significance of honeycombing on chest CT?
Honeycombing on CT is seen as rows of round dark areas with similar size and with relatively thin walls. Honeycombing indicates end-stage fibrosis of the lung, and is a very bad prognostic sign, often seen in UIP/IPF, particularly if it is in a peripheral distribution.
b) How can you tell ground glass opacity from airspace disease on CT?
Ground glass opacity does not obscure the vessels in the involved area, while airspace disease obscures vessel margins.
c) What does ground glass opacity indicate in terms of pathology?
Ground glass opacity is very nonspecific, and can be seen in edema, infection, fibrosis or tumor.
d) How can air-trapping be detected on CT?
Air-trapping may be suspected if the lung appears very heterogeneous in density on standard CT images. However this appearance may be due to ground glass opacification of lobules, so to specifically identify air-trapping, expiratory images are most helpful. Expiratory images should show uniform increase in all of the lung opacity, so if there are lobules that remain dark on expiration, this indicates air trapping.
e) What is the virtue of prone CT imaging of the lung?
Because there is often vague density that looks like ground glass opacity in the dependent part of the lung (posteriorly, in the usual supine scan position), if you turn the patient prone, this area should resolve. If not, then it is actual lung abnormality.
Question 4:
a) What are specific imaging findings that suggest the diagnosis of scleroderma?
Scleroderma may be suggested if pulmonary fibrosis is demonstrated with a marked basilar predominance, and if there is also dilatation of the esophagus, since this condition is associated with GI dysmotility.
b) What are specific imaging findings that suggest the diagnosis of silicosis?
The lung findings in silicosis are very variable, and can include fibrosis, masses and emphysema. But presence of enlarge hilar nodes, particularly if they show peripheral calcification (eggshell), can be suggestive of silicosis in the appropriate clinical setting.
c) What are specific imaging findings associated with hypersensitivity pneumonitis?
The imaging diagnosis of hypersensitivity pneumonitis is very difficult, and the findings even on CT may be very subtle and may overlap with other fibrotic lung diseases. The finding of air trapping, which requires special imaging at expiration, is suggestive of the diagnosis.
d) How do imaging findings of COVID and TB differ?
COVID often demonstrates extensive ground glass opacity, and can also include airspace/alveolar disease. Lung findings may progress rapidly. Tuberculosis (TB) can have many appearances on imaging, including diffuse miliary disease or lobar airspace disease. The presence of enlarged hilar nodes is highly suggestive of TB and imaging findings generally do not change rapidly.
e) What is a reliable online resource to assist in selection of appropriate imaging for all of these conditions?
The American College of Radiology Appropriateness Criteria are a clinically-oriented resource freely available to everyone online, and includes assessment of appropriate imaging for common symptom sets, as well as information on radiation dose and patient preparation.
This completes the Pre-Class material on Imaging of Interstitial vs Airspace Disease.
You will apply this knowledge in the second In-Class Interactive session. You will get more out of this session if you have reviewed this material before coming to class.
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