Left upper lobe atelectasis

Lateral view of left upper lobe atelectasis. The left hemithorax is occupied mostly by the hyperexpanded left lower lobe. The major fissure is markedly displaced anteriorly and delineates the collapsed left upper lobe, which is pancaked ventrally (arrows). Anterior to the collapsed left upper lobe, the hyperexpanded anterior segment of the right upper lobe is accounting for the retrosternal lucency (arrowhead) and for the clear outline of the ascending aorta.