Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral chest radiographs were obtained . Lung volumes remain low . The previous noted left lower lung opacity is less conspicuous on this repeat study , and was likely artifactual due to rightward rotation . On the lateral view , there is now a retrocardiac opacity without clear correlate on the frontal view , which was also present on prior radiographs . The cardiomediastinal silhouette and hilar contours are unchanged . There is no pleural effusion or pneumothorax .
    OUTPUT:
    
Retrocardiac opacity without clear correlate on frontal radiograph of unclear significance . However in the appropriate clinical setting , this can represent pneumonia .