What is the typical imaging sign on CT for early invasive pulmonary aspergillosis?

What is the typical imaging sign on CT for early invasive pulmonary aspergillosis?

• A. Cavitation with air crescent
• B. Pleural effusion
• C. Tree-in-bud nodularity
• D. Halo sign (ground-glass halo around a nodular lesion)

Answer: (D)

The imaging sign being tested is the halo sign: a nodule with a surrounding ground-glass halo. This pattern reflects hemorrhage around a focus of fungal invasion of blood vessels by Aspergillus, which is characteristic of early invasive pulmonary aspergillosis in immunocompromised patients. It appears early because it shows vascular invasion and hemorrhagic edema before the lesion progresses to necrosis and cavitation. Cavitation with an air crescent tends to appear later, after some necrosis has occurred and as the patient’s immune status changes. Pleural effusion can occur but is nonspecific and not the hallmark of early IPA. Tree-in-bud nodularity points to small-airway processes and bronchiolar infection, not the classic angioinvasive pattern of IPA. So the halo sign best captures the early CT hallmark of this infection.

The imaging sign being tested is the halo sign: a nodule with a surrounding ground-glass halo. This pattern reflects hemorrhage around a focus of fungal invasion of blood vessels by Aspergillus, which is characteristic of early invasive pulmonary aspergillosis in immunocompromised patients. It appears early because it shows vascular invasion and hemorrhagic edema before the lesion progresses to necrosis and cavitation. Cavitation with an air crescent tends to appear later, after some necrosis has occurred and as the patient’s immune status changes. Pleural effusion can occur but is nonspecific and not the hallmark of early IPA. Tree-in-bud nodularity points to small-airway processes and bronchiolar infection, not the classic angioinvasive pattern of IPA. So the halo sign best captures the early CT hallmark of this infection.