Left upper lobe collapse has distinctive features but can be challenging to identify on chest radiographs by the uninitiated.
For a general discussion refer to the article on lobar collapse.
The left upper lobe collapses anteriorly becoming a thin sheet of tissue apposed to the anterior chest wall, and appears as a hazy or veiling opacity extending out from the hilum and fading out inferiorly 1. It thus reverses the normal slight increase in radiographic density seen as you move down the lung (due to increased thickness of the chest soft tissues).
Parts of the normal cardiomediastinal contour may also be obliterated where the left upper lobe, particularly the lingula abut the left heart border. The anterior parts of the aortic arch are also often obliterated from view.
In some cases the hyperexpanded superior segment of the left lower lobe insinuates itself between the left upper lobe and the superior mediastinum, sharply silhouetting the aortic arch and resulting in a lucency medially. This is known as the luftsichel sign 1.
The left hilum is also drawn upwards, resulting in an almost horizontal course of the left main bronchus and vertical course of the left lower lobe bronchus 1.
Non-specific signs indicating left sided atelectasis will also be present, including:
- elevation of the hemidiaphragm
- 'peaked' or 'tented' hemidiaphragm: juxtaphrenic peak sign
- crowding of the left-sided ribs
- shift of the mediastinum to the left
On lateral projections the left lower lobe is hyperexpanded and the oblique fissure displaced anteriorly. There is associated increase in the retrosternal opacity.