Figure 38A: Posteroanterior (PA) plain film of the chest (left). There is a dense round opacity (yellow arrow) in the right lung base containing a small air-fluid level. Axial CT image of the chest (right). The spherical opacity is in the right lower lobe, and the air-fluid level (blue arrow) is again noted.

Lung abscess, empyema, bronchogenic carcinoma, pulmonary metastasis, diaphragmatic hernia.