Which one of the following CT scans shows an empyema? A or B

A shows the empyema. It has a lenticular shape and smooth, uniform walls formed by the thickened pleura, which seems to split around the empyema (i.e., the split pleura sign). The adjacent lung tissue is compressed.

B shows a lung abscess. It is spherical and has thick, irregular walls, often containing air bubbles. The adjacent lung tissue is less compressed; the abscess may be surrounded by airspace disease.