FINDINGS:
There is dense retrocardiac opacity silhouetting the descending
 thoracic aorta and medial hemidiaphragm compatible with a left lower lobe
 consolidation.  Elsewhere, the lungs are clear.  The cardiomediastinal
 silhouette is within normal limits.  Osseous and soft tissue structures are
 unremarkable.

IMPRESSION:
Left lower lobe consolidation compatible with pneumonia. 
 Recommend repeat after treatment to document resolution.