What could problem possibly be?

A 44-yr-old preop….comparison April 22, 2015….. findings: frontal and lateral views of the chest demonstrate normal heart size and pulmonary vascularity. The lungs are well expanded. A poorly-defined opacity is seen on frontal projection, which overlies the anterior portion of the right 4th rib. This could represent an abnormality within the rib or an unerlying parenchymal abnormality. Consider followup CT scan for further characterization of this. Skeletal structures are otherwise unremarkable.
WHAT COULD THEY POSSIBLY BE LOOKING FOR?