Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: PA and lateral views of the chest were obtained . The heart is top normal in size . Mediastinal contour is stable . Lungs are clear . A nodular density projecting superior to the left posterior fourth rib was present on the prior examination and is grossly unchanged . There is no pleural effusion or pneumothorax . Old right - sided rib fractures are again noted .
    OUTPUT:
    
No acute intrathoracic abnormality .