Monod sign (lungs)

Last revised by Liz Silverstone on 6 Mar 2024

The Monod sign describes gas that surrounds a mobile fungus ball or mycetoma (most commonly an aspergilloma) in a pre-existing pulmonary cavity 1-3.

Terminology

In the 2024 edition of the Fleischner glossary, air crescent is the preferred term applying to air crescents seen with both mobile intra-cavitary fungus balls and retracted infarcted lung (usually fixed in position), as seen in recovering angioinvasive aspergillosis 4.

History and etymology

The sign was first described by the French physicians G D Pesle and Olivier Monod in 1954 6.

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