Hemithorax white-out – it is not hard to detect a completely opacified hemithorax, however determining the underlying cause by assessing secondary signs is more of a challenge. The position of the mediastinum and trachea is the key. A large pleural effusion will expand the hemithorax and push the trachea away (left image). Conversely, a completely collapsed lung has reduced volume and will pull the trachea towards the white-out (right image), as will a pneumonectomy. A completely consolidated lung (eg. pneumonia) will have preserved volume and therefore the trachea will remain midline.
from our tumblr blog: http://radiologysigns.tumblr.com/post/24852717957
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