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Monod sign (lungs)

The Monod sign (often misspelt Monad sign) simply describes gas that surrounds a mycetoma (most commonly an aspergilloma) in a pre-existing pulmonary cavity 1-3.

It should not be confused with the air crescent sign which is seen in recovering angioinvasive aspergillosis 4. The air crescent sign heralds improvement in the condition.

In practice, it is likely that the term Monod sign will receive blank stares. The gas around the mycetoma is often crescent-shaped and hence, the term air crescent sign is used interchangeably by many to refer to both pathological processes.

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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Article information

rID: 1689
System: Chest
Section: Signs
Tag: lung
Synonyms or Alternate Spellings:
  • Monod's sign
  • Monad sign

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Cases and figures

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