Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP portable view of the chest . There is subtle retrocardiac opacity which appears to silhouette the descending portion of the thoracic aorta . Elsewhere the lungs are grossly clear . Cardiomediastinal silhouette is within normal limits . No acute osseous abnormality detected .
    OUTPUT:
    
Possible retrocardiac opacity for which two - view chest x-ray suggested if patient is amenable .