Air crescent sign
Pattern seen in radiologic examinations
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In radiology, the air crescent sign (also called the Monad sign[1]) 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.[2] Classically, it is due to an aspergilloma, a form of aspergillosis, that occurs when the fungus Aspergillus grows in a cavity in the lung.[3]
| Air crescent sign | |
|---|---|
| |
| The arrows denote an ill-defined nodular opacity in the medial aspect of the right upper lobe with an ill-defined rim of lucency surrounding it. | |
| Differential diagnosis | Aspergilloma |
Air crescent sign has also been reported in conditions such as tuberculosis, granulomatosis with polyangiitis, intracavitary hemorrhage, and lung cancer.[4]
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