Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The mediastinum appears widened especially comparatively to the most recent prior chest x-ray however some of this may be due to low lung volumes . The lungs are clear . There is no evidence of pneumonia , pneumothorax , or pleural effusion .
    OUTPUT:
    
Widened mediastinum which could be secondary to many factors including low lung volumes however acute aortic pathology can not be ruled out on the basis of this radiograph . On attending readout comment is also noted that the tissue posterior to the sternum was thickened . All these findings are probably due to low lung volumes and a repeat PA and lateral radiograph with full inspiration would be able to better assess the situation . Updated findings after attending readout discussed with ___ at 8 :36 AM via telephone . Initial findings discussed with ___ at 5 :20 AM via telephone .