Left upper lobe collapse has distinctive features but can be challenging to identify on chest radiographs by the uninitiated. Hence it is a classic CXR case for radiology fellowships exams.
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 left 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). This is known as veiling density and can be subtle.
Parts of the normal cardiomediastinal contour may also be obscured where the left upper lobe, particularly the lingular segments, abuts the left heart border. The anterior parts of the aortic arch are also often obscured.
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 sickle-shaped lucency medially. This is known as the luftsichel sign 1.
If the collapse is not great enough, the hyperinflated superior segment of the left lower lobe may cause an apparent apical cap, which can be mistaken for pleural fluid or thickening or even a Pancoast tumor 2.
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 ribs
- shift of the mediastinum to the left
- posterior and left lateral rotation of the heart
On lateral projections the left lower lobe collapse causes increase retrosternal density and the oblique fissure displaced anteriorly. There is associated anterior displaced of the left hilum.
- triangular opacification in axial images, thinner at the hilum
- the oblique fissure rotates anteromedially
- left upper lobe consolidation with absence of signs of volume loss
- 1. Collins J, Stern EJ. Chest radiology, the essentials. Lippincott Williams & Wilkins. (2007) ISBN:0781763142. Read it at Google Books - Find it at Amazon
- 2. Webb WR, Higgins CB. Thoracic Imaging, Pulmonary and Cardiovascular Radiology. Lippincott Williams & Wilkins. (2010) ISBN:1605479764. Read it at Google Books - Find it at Amazon
- 3. Clarke C, Dux A. Chest X-Rays for Medical Students. Wiley. (2011) ISBN:0470656190. Read it at Google Books - Find it at Amazon
Related Radiopaedia articles
- airspace opacification
- differential diagnoses of airspace opacification
- lobar consolidation
- lobar lung collapse