Figure 15a. Cavitary tuberculosis associated with aspergilloma. (a) Frontal radiograph shows a cavity in the left upper lobe (black arrow) with a dependent area of soft-tissue opacity (solid white arrow). The crescentic area of hyperlucency (open arrow) represents residual air in the cavity and is referred to as the air crescent sign. (b) Axial CT scan shows dependent soft-tissue aspergilloma (black arrow) within the cavity (solid white arrow), along with the air crescent sign (open arrow).