What is a fungus ball, and if it is suspected, what imaging-based maneuver can be performed to confirm the suspicion?
A fungus ball is a discrete mass of intertwined fungal hyphae mixed with mucus, cellular debris, and fibrin and is also known as an aspergilloma (because it is typically due to Aspergillus fumigatus ) or a mycetoma. It represents a noninvasive form of infection that occurs in structurally abnormal lungs, usually a preexisting cavity, in an immunocompetent host. One will see an air cyst, cavity, or bronchiectatic segment in the lung containing a dependent nodule that represents the clumped fungus ( Figure 18-15 ). The nodule is typically not adherent to the surrounding wall, which is in contradistinction to a lung cancer that could develop in a preexisting cystic space. One could therefore image the patient in the supine and prone positions to verify that the nodular filling defect is mobile, which would confirm a fungus ball.