There are numerous causes of white shadowing in the lungs including:

• consolidation
• pleural effusion
• collapse
• pneumonectomy
• specific lesions e.g. tumours
• fluid e.g. pulmonary oedema

If there is a 'white-out' of a hemithorax it is useful to assess the position of the trachea - is it central, pulled or pushed from the side of opacification.