A pulmonary mycetoma, also known as a fungus ball, is due to colonization of a pre-existing cavity by a fungus, usually a species of Aspergillus, in which case it is termed an aspergilloma 1.
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Terminology
Pulmonary mycetoma is unrelated to soft-tissue mycetoma, also known as Madura foot. The latter is due to traumatic innoculation of bacteria or fungi into soft-tissues in tropical and subtropical regions.
According to the 2024 Fleischner glossary, the term "air crescent" can be used for both mobile and fixed intracavitary bodies. "Monod sign" does not appear in the glossary 1.
Pathology
The mass consists of tangled hyphae stuck together by mucus, fibrin and cell debris.
Radiographic features
Chest radiographs and CT demonstrate a round intracavitary mass which is often mobile and maintains a dependent position. An air crescent may separate the mass from the cavity wall. The internal structure can appear sponge-like and may contain calcification 1-3.