Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Heart size is normal with mild tortuosity of the thoracic aorta . Hilar contours are unremarkable . Lungs are clear . Pleural surfaces are clear without effusion or pneumothorax . On lateral view a roughly 2 .6 cm extrapleural density is seen immediately posterior to the sternal angle .
    OUTPUT:
    
2 .6 cm extrapulmonary mass or cyst immediately posterior to the sternal angle of unclear etiology . Recommend further evaluation with non-urgent CT .