Discussion
This radiograph demonstrates left upper lobe collapse. This is one of the more challenging lobar collapse patterns to recognize on AP or PA radiographs as the left upper lobe collapses anteriorly and superiorly and ends up superimposed over the inflated left lower lobe. Other than the increased opacity over the left hemithorax, other notable features present on this radiograph are a left juxtaphrenic peak sign and silhouetting of the left heart border and hilum by the collapsed left upper lobe.
When this finding is identified, the cause of the collapse should be further investigated with CT. This case was post-obstructive collapse secondary to a central obstructing mass. The mass is not well visualized on this radiograph.