Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Cardiac , mediastinal and hilar contours are normal . The pulmonary vasculature is normal . Patchy opacity within the retrocardiac region most likely reflects atelectasis though infection is not excluded in the correct clinical setting . No pleural effusion , pulmonary edema or pneumothorax is seen . There are no acute osseous abnormalities .
    OUTPUT:
    
Patchy retrocardiac opacity , likely atelectasis . Infection however in the correct clinical setting is not excluded .