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Air crescent (lung)

Last revised by Liz Silverstone on 11 Aug 2024

Citation, DOI, disclosures and article data

Citation:

Gaillard F, Silverstone L, Bickle I, et al. Air crescent (lung). Reference article, Radiopaedia.org (Accessed on 06 Oct 2024) https://doi.org/10.53347/rID-869

DOI:

https://doi.org/10.53347/rID-869

Permalink:

https://radiopaedia.org/articles/869

rID:

869

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:

11 Aug 2024, Liz Silverstone ◉ ◈

Disclosures:

At the time the article was last revised Liz Silverstone had no financial relationships to ineligible companies to disclose.

View Liz Silverstone's current disclosures

Revisions:

26 times, by 15 contributors - see full revision history and disclosures

Systems:

Chest

Sections:

Signs

Tags:

lung, infectiousdisease

Synonyms:

Causes of an air crescent sign
Air meniscus sign
Pulmonary air meniscus sign

Air crescent describes the crescent of gas between an intra-cavitary mass and the cavity wall. The intra-cavitary mass may be due to necrotic tissue or a fungus ball ⁶.

Terminology

The descriptor Monod sign ² is commonly used to describe the combination of a gas crescent and a mobile fungus ball. The 2024 Fleischner glossary no longer includes this term and uses ‘air crescent’ to refer to gas in cavities that contain mobile fungal balls as well as those that contain fixed infarcted tissue ⁸.

Pathology

Etiology

Common causes include angio-invasive aspergillosis with retraction of infarcted lung, fungal colonization of a preexisting cavity or blood clot ⁸. Fungal balls can be mobile.

Causes include ⁵:

fungal colonization including aspergilloma
angioinvasive aspergillosis
hydatid cyst
other rare causes
- pulmonary tuberculosis
- Rasmussen aneurysm in a tuberculous cavity
- pulmonary abscess
- lung cancer
- pulmonary hematoma
- Pneumocystis jirovecii pneumonia (PJP)

In angioinvasive fungal infection, the nodules are composed of infected hemorrhagic and infarcted lung tissue. As the neutrophil count recovers and the patient mounts an immune response, peripheral reabsorption of necrotic tissue causes the retraction of the infarcted center and air fills the space in between ⁷. This creates an air crescent within the nodules and is a good prognostic finding because it marks the recovery phase of the infection. This sign is seen in ~50% of patients ².

References

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