In radiology, the air crescent sign (also called the Monad 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. Classically, it is due to an aspergilloma, a form of aspergillosis, that occurs when the fungus Aspergillus grows in a cavity in the lung.
Air crescent sign has also been reported in conditions such as tuberculosis, granulomatosis with polyangiitis, intracavitary hemorrhage, and lung cancer.
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External links Air crescent sign on CXR Air crescent sign on CT