Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: AP and lateral chest radiographs were provided . There is a retrocardiac opacity at the left lung base which is nonspecific and may represent atelectasis versus infectious process . There are no other focal consolidations seen . There is a small left pleural effusion . There is no pneumothorax . Cardiomediastinal silhouette has a left ventricular configuration . Median sternotomy wires are seen . There is no evidence of CHF . There are multiple old healed rib fractures on the right as well as old fracture of the right humeral head .
    OUTPUT:
    
Retrocardiac opacity at the left lung base which is nonspecific and may be atelectasis ; however , can not rule out infectious process .