Monod sign (lungs)

Last revised by Benjamin Layton on 4 Aug 2022

Citation, DOI, disclosures and article data

Citation:

Gaillard F, Layton B, Skandhan A, et al. Monod sign (lungs). Reference article, Radiopaedia.org (Accessed on 28 Mar 2023) https://doi.org/10.53347/rID-1689

DOI:

https://doi.org/10.53347/rID-1689

Permalink:

https://radiopaedia.org/articles/1689

rID:

1689

Article created:

2 May 2008, Frank Gaillard ◉ ◈

Disclosures:

At the time the article was created Frank Gaillard had no recorded disclosures.

View Frank Gaillard's current disclosures

Last revised:

4 Aug 2022, Benjamin Layton

Disclosures:

At the time the article was last revised Benjamin Layton had no recorded disclosures.

View Benjamin Layton's current disclosures

Revisions:

34 times, by 12 contributors - see full revision history and disclosures

Systems:

Chest

Sections:

Signs

Tags:

lung

Synonyms:

Monod's sign
Monad sign

The Monod 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.

The sign implies a freely mobile mass, which moves on mobilizing the patient. This is best demonstrated by acquiring images in a prone position, causing the mass to fall, to a gravity-dependent location and favoring a Monod sign; as compared to an air crescent sign.

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.