Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest were obtained . A subtle patchy left basilar retrocardiac opacity is seen , nonspecific , could be due to atelectasis , although a pneumonia is not excluded in the appropriate clinical setting . No pleural effusion or pneumothorax is seen . Cardiac and mediastinal silhouettes are stable and unremarkable . Old right - sided rib deformity at approximately the right lateral eighth rib is noted .
    OUTPUT:
    
Patchy left basilar retrocardiac opacity could be due to atelectasis or pneumonia .