This is the classical appearance of left upper lobe collapse. There is a veil-like opacity obscuring the left hemithorax. The left heart border is indistinct, there is volume loss indicated by a raised left hemidiaphragm, mediastinal shift to the left and rib crowding. The sagittal CT scan shows why you get a veil-like opacity - the left lower lobe is ensuring partial aeration accross the hemithorax. There is a large mass at the hilum obstructing the left upper lobe bronchus. The left upper lobe collapses anteriorly. For further information and links to related articles see Patterns of lobar collapse.