Case 4
These two different cases demonstrate imaging findings of another pattern of lung disease that can lead to useful differential diagnoses: ground glass opacity (GGO for short).
Question 1:
How can you distinguish GGO from airspace disease? Which type of imaging would you predict would diagnose GGO best--CXR or CT? What is the distribution of disease on this CXR?
GGO is overall less dense than airspace opacity, so the vessels of the lung can be seen even in the areas of abnormality. With airspace disease, the involvement is typically so dense that it obscures vessels. GGO is usually best seen with CT, unless it is very extensive, as in Case A below (which was due to eosinophilic pneumonia). The distribution of GGO is peripheral, which is somewhat unusual, and suggests eosinophilic lung disease.
Case 4
These three images show CT of GGO.
Question 2:
For each study, what diagnoses would you consider if: the patient had fever vs no fever but just cough and weight loss? What looks different on the airspace example compared to GGO?
On case A, there are many rounded nodules, some large enough to be masses. There is surrounding GGO. For fever, you might consider TB or fungal infection, but for cough and weight loss, metastases with surrounding hemorrhage (GGO can represent blood) would be more likely. On Case B there are many areas of GGO, interspersed with relatively normal looking lung. For fever, you could consider atypical pneumonias, but for cough and weight loss, might consider hypersensitivity or a tumor like lung cancer or lymphoma. For case C, a small patch of GGO was found on a screening CT. For fever, again this could represent a focal area of early atypical pneumonia, but cough and weight loss makes lung cancer a concern. Note that you can still see vessels in the areas of GGO on all three cases, but not on the airpace disease example (which was pulmonary lymphoma). It is important to realize that GGO has a wide number of causes, and can involve airspaces, interstitium, or both. The process is just occurring at such a microscopic level that it produces a grainy grey opacity rather than the macroscopic changes we see in airspace filling or interstitial thickening involving larger structures.
