<num>. increased interstitial abnormality since prior radiographs. although an etiology such as mild vascular congestion or atypical infection could explain the change, since the distribution is very similar, worsening of a underlying interstitial disease is probably the most likely reason. <num>. new or increased retrocardiac opacity. differential includes atelectasis, focal area of interstitial change and fibrosis, but possibly superimposed infectious process. correlation with clinical presentation is suggested.