Given the patient's history, how would you diagnose the lesion?
Given the patient's history, the most likely lesion would be a metastasis, but a ground glass halo is unusual for most metastases. Given the ground glass halo, a differential is required, which might include: 1) atypical presentation of rectal carcinoma metastasis; 2) infectious nodule (such as fungal infection); 3) septic embolus; 4) new primary lung tumor (e.g. BAC, although unlikely given quick onset); or 5) the odd possibility of a metastasis from a second primary... one that is more likely to present with a ground glass halo (e.g. melanoma or lymphoma).
If there were two nodules with a ground glass halo, would that change your differential?
New primary lung cancer(s) would move lower on the differential, but otherwise the differential would still stand.
Pretend a single nodule *without* a ground glass halo was seen on the initial staging study for this patient, what is the likelihood it would represent a metastasis?
The answer in general depends on the primary, but the odds of it representing a metastasis are around ~50% (Ref. 1)
There is a 6 mm nodule in the left lower lobe, with faint surrounding ground glass attenuation, which is new compared with a CT chest from 5 months prior.