Unusual Air Crescents on Chest Radiographs.

The air crescent (AC) is a common radiological sign. Even if its commonest aetiology remains pulmonary aspergillosis, various other causes have been described. In this study, we report four rare causes of ACs seen on chest radiographs that haven't been described in the literature. Teaching point: The differential diagnosis of an air crescent sign on chest radiographs includes oesophageal bezoar, interstitial lung emphysema, central bronchial stenosis and perforated emphysematous cholecystitis.