label: Air crescent
label_lc: air crescent
description: "An air crescent is a collection of air in a crescentic shape that separates the wall of a cavity from an inner mass. The air crescent sign is often considered characteristic of either Aspergillus colonization of preexisting cavities or retraction of infarcted lung in angioinvasive aspergillosis. However, the air crescent sign has also been reported in other conditions, including tuberculosis, Wegener granulomatosis, intracavitary hemorrhage, and lung cancer."