air crescent sign

{{Short description|Pattern seen in radiologic examinations}}

{{distinguish|text=the crescent sign}}

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|image = Air crescent sign.jpg

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|caption = The arrows denote an ill-defined nodular opacity in medial aspect of right upper lobe with ill-defined rim of lucency surrounding it

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|differential = Aspergilloma

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In radiology, the air crescent sign is a finding on chest radiograph and computed tomography that is crescenteric and radiolucent, due to a lung cavity that is filled with air and has a round radiopaque mass.{{cite journal |author =Abramson S |title=The air crescent sign |journal=Radiology |volume=218 |issue=1 |pages=230–2 |date=January 2001 |pmid=11152807 |doi= 10.1148/radiology.218.1.r01ja19230|url=http://radiology.rsnajnls.org/cgi/pmidlookup?view=long&pmid=11152807|url-access=subscription }} Classically, it is due to an aspergilloma, a form of aspergillosis, that occurs when the fungus Aspergillus grows in a cavity in the lung.{{cite journal |vauthors =Curtis AM, Smith GJ, Ravin CE |title=Air crescent sign of invasive aspergillosis |journal=Radiology |volume=133 |issue=1 |pages=17–21 |date=October 1979 |pmid=472287 |doi= 10.1148/133.1.17}}

It is also referred as Monad sign.{{cite web|last1=Goel|first1=Ayush|title=Pulmonary aspergillosis|url=http://www.mediconotebook.com/2015/05/pulmonary-aspergillosis.html|website=Mediconotebook|access-date=29 May 2015}}